aurora - NTRS - NASA

N64-28080

,%

X4n1-64-97

g IACCESSION

NUMDER)

HRU| (PAG_

TMX-55041

(CODE) m

..a_ y-Ss_ '-//

,J

" rJ

LINASA -

CR

OR

TMX

Gl_

AD

/_" ¢CAT_GORY)

I_UMBI_RI

k-

AURORA

BY BENGT

HULTQVIST Q

oTS

XER OX MICROFILM

pp, l CE

$ $

APRIL1964

GODDARD SPACEFLIGHTCENTER GREENBELT, MARYLAND

(Goddard

Energetic

Particles

Preprint

Series)

AURORA

a review

Bengt

Goddard

;_NASA-National Post-Doctoral Kiruna

Academy Resident

Geophysical

Hultqvist_

Space

Greenbelt,

by

Flight

of Sciences-National Research

Observatory,

Center

Maryland

Associate Kiruna,

Research on leave Sweden

Council of absence

Senior from

TABLE

I.

Introductory

Description

1. 2.

and Energy Considerations and Classification of Aurora

Intensity Definition

3.

The

4.

Auroral

5.

Emission

6.

Methods

.....................

Development

of

Forms Spectrum of

Figure

1.

for of

Geographical (a)

Introduction

(b)

Observed Latitudinal

Aurora

...................

Section

l and

Aurora

of

.......................

Type

Effects

(f)

Inner

Auroral

of

Time

Seasonal

(c)

Sunspot

Orientation

Activity

Auroral of Visual

of Observational Theoretical Curves

Variation

(b)

17 .........

Zones Auroral

and

Auroral

Zones

Recurrence Variation

on

the

Auroral

of Visual Tendency.

25

27

Activity

Auroral

........

Activity

......

..............

28 31 31

....................

Arcs

20

Z5

31

.................

3Z

.................

3Z

Average

(b)

Diurnal Variation in the Orientation in and the Auroral Zones ................... Discussion Auroral

Orientations

Location

with

...................

Variation

of Auroral

Zones

..................

of Visual

Variations

Cycle

Zone

Auroral ..............

(a)

(c)

17

18

Cycle

Day

16

.........................

Auroral

27

............

17

(e)

(a}

Figures

Auroral

the

Dependence

Other

14

........................ Locations of Distribution

(d)

3.

for

..................

Comparison Various

Diurnal

6 lZ

Visual

(c)

2.

...........

7

Distribution

Solar

Z 4

Display

Studies

Visual

Activity

4.

Auroral

............. ...........

......................

Recording

Captions

Morphology

an

1

........................

Morphological

2.

OF CONTENTS

...................

of the Diurnal Variation Zones .....................

Near

33 Near 34 the 37

(d) Diurnal Variation on the Central Auroral Caps ..... (e) Other Variations in Arc Orientations .......... 5. The Height and Vertical Extent of Visual Aurora 6. Motions ............................

40 41

......

41 44

(a) Changes in the Geographical Pattern of Auroral Activity ........................ (b) Motion of Indivudual Auroral Forms .... ...... 7. Dynamic Morphology of Individual Auroral Displays Figure Captions for Section 2 and Figures ........... 3. Correlation

with

and

Disturbances

Geophysical

Phenomena

....

49 52

......

57

I.

Solar

2. 3.

Geomagnetic Disturbances .................. Earth Currents ........................

57 59

4.

Radio

59

Aurora

5.

Bremstrahlung

6.

Auroral

7. 8.

Ionospheric Scintillation

9. i0.

Radio-Noise Auroral

Figure

57

......................... X-rays

at Balloon

Altitudes

61

2.

Observed

..................

64

• •

.......................

for Section

3 and

Fluxes

and

Energy

into the

Figures

............

68

Associated 71 71

Spectra

Upper

65 66

.........................

Precipitated (a)

.....

65

Observations of Energetic Particles Aurora ..........................

Introduction

60

.......................... Emission

I.

.........

......................

Disturbances Associated with Aurora of Radio Waves from Radio Stars and

"Sound"

Captions

Direct with

......................

Absorption

Satellites

4.

Solar

44 46

of Electrons

Atmosphere

.........

71

Latitudinal Distribution and Other Spatial Characteristics ....................

72

(b)

Time

Characteristics

75

(c)

Pitch

Angle

(d)

Kp -dependence

(e)

The

Spectrum

3.

Observed

Fluxes

4.

Quantitative

Precipitated and

Photon

of Precipitation

Distribution

.................

of Precipitation of Precipitated and

Energy

Emission

Between

Electrons

ii

........

76 77

of Protons .............

Electron

in Aurora

75

.............

Spectra

into the Atmosphere Relations

.........

79

Precipitation

..............

80

5.

Relation

of Precipitated

Radiation Fi'gure So

Captions

Theoretical

Introduction

2.

Some

3.

Closed

4.

Model

Acknowledgements Captions

References

4 and

Figures

82 ............

of the

the

Theoretical

Models

88 Problem

................

Solar

Plasma

Field

.....................

Penetrating

Section

5 and

............................

111

Figures

......

89 90

into the 94

........................ for

87 88

.........................

Magnetosphere with

Outer

.......................

Specifications

Geomagnetic

to the

.........................

for Section

Models

I.

Figure

Belt

Electrons

96 ...........

97 98

i.

Descriptions most (ca

famous

B.C.)),

Pliny

A.D.)),

and

15 (Ca.

sidered

63

In northern

stitions

did not

remarkably

The

and he recent

first

by 1963)

the

northern

analogy

with

australis. the is

upper events

them.

tacular

glow

"The

Merry

isles

of

aurora

the has

explosions. 1958,

French

and

is

of

they

a display

(after made

and

first

by

can

title,

the

Jacka

andPaton,

which

the

aurora 1958).

since

dawn,

by

with

so

it

is

was

of

In

called

aurora

it

latitudes.

those

is

It

parts

of

the

of

the

concealed

no

longer

is

more

known

in In

an aptly

the the

high-altitude

observed

mostly

occasions

1963). use

latitudes.

frequently it

and

been and

is

higher

see

have appearance

been

rare

more

(5acka

latitudes at

are

to

medium

the

(1955)

of

usual

have

super-

extent. chronicle

events

the

middle

on

name

artificial

Waddington,

its like

man

in

overhead

horizon,

belies the

Britain"

is

such

St6rmer

1621,

lights

observers

the

horizon,

Dancers,"

been

which

latitude

then

the

in

observed from

and

same

seems

of

southern seen

by

dawn,

equatorwards

below

Aurora

northern

are

from

common to the

14 con-

superstitions

auroral

Gassendi

the

were

quoted

of

33

auroras

in the Norwegian

description

dawn

middle being

The Fowler

when

moves

that

on

or

and

I, Chaps.

more

It is partly

appropriate

northern

aurora

be found

Z7

5

Book

descriptions

by

are

descriptions

borealis

the

observation

philosopher

an

lights aurora

which,

can

good

and

auroras

1250.

borealis,

the

portion when

display from

aurora

"The

only

great

some

name

used

Paton, of

quotes

rare

of the

I, Chap.

II, Chaps

characterized

objective

description of about

the

Some

Book

Book

calamities

where the

known.

Naturales,

Europe

are

Europe

Mirror

also time.

The

coming

influence good

King's

Naturalis,

(Quaestiones

especially,

are

(Meterologica,

In central

for

Ages,

antiquity

Aristotle

(Historia

A.D.)).

Description

of great

by

Seneca

as warnings

Middle

fears.

A

those

77

and

the

of aurora

are

340

(ca.

Introductory

unspeccalled

northern last

years

nuclear in

1958

(Cullington,

This

review

influenced few

by

years.

the

the geomagnetic

auroral

1951;

and

which

is largely

ellite

studies

detail,

the

spectrum,

phenomena,

The

determined

they

above.

Finally,

nomena

will be

results

obtained

of auroral

1955;

Chamberlain, to them

for

studies, will be

here

the geomagnetic particles in the

theoretical

discussed

are

in the

last

have

1961)

some

details

on,

correlations on

the

field.

will

which

phenomena

morphological

contained

proposed briefly

on

emphasis by

not

characteristics

is referred

auroral

are

and

reviews

St6rmer,

older

etc.

auroral

field

reader

of primary

since

on

extensive

(Harang,

recently,

other

concentrate

Excellent

appeared, fairly

will

also

with

morphology,

Rocket

be

e.g.,

and

treated

sat-

in some

extensivetreatisesmentioned

models

for

in relation

various

to the

auroral

phe-

observatio/is.

Z/ In this first teristics

i.

will

Intensity

subsection

be

given.

and

Energy

Aurora sky,

as

aurora

value).

the value The

majority

down

For

used:

Way;

provides These effort been

estimation four

equal

to place slightly

brightness equal

in terms

of aurora

by

for

intense

the than

to the full moon. the whole

visual

of the

is equal

at the

on

more

and

Brightness

Hunten

of number

emission IBC

scale by

weaker

International

extremely

IBC

even

in the

except

scale

exists.

to that of moonlit

the

charac-

phenomena 1960,

are

aurora

to that of thin moonlit

illumination are

luminous

fully comparable

however,

airglow

of an

modified

important

are

of brightness

definitions

of _-a'u_ral

Friedman,

auroras

They

are,

of the

classes

I, the

intense

1 (after

strongest i.

of auroras

a total

definitions most

very

in Table

II, brightness

brightness

of the most in Table

to the intensity

following are

The

given

description

Considerations

is one

is illustrated

a short

an

clouds; equivalent

absolute

(1955), of photons

in aurora)

to that of the

ground

Seaton

per

and

IV,

the

Milky III, aurora

to full moonlight. made

His

proposedO

ofk cm

clouds;

(1954)

basis.

who

the (IBC)

cirrus

cumulus

crude.

observers, Coefficient

a first

results

have

the following

5577A

(generally

2 (column)

and

I

i09

= 1 kR

II

101°

= i0 kR

III

1011

= i00

IV

1012

= 1000

kR kR

sec.

the

Table 1 Source

Flux (ergs cm -2 sec -1) 1.4

Sun

Full

moon

Strong

aurora

Total

starlight

Airglow

OH

(visible)

{infrared)

Lyman-=

• lO s

3000.

10 -3

1000"

10 -3

1.8

• 10 -3

16

• I0 "a

19

• 10 -3

I0

• i0 -3

0.I

" 10 -3

3.8

• I0 -3

o

Celestial

Cosmic

sources

rays

{1230-1350A)

106 photons/cm 2 (column) sec is called 1 Rayleigh (1R) in accordance with the proposal of Hunten et al. (1956). (For a discussion of the Rayleigh unit see also Chamberlain, 1961, Appendix II). The Rayleigh unit is not limited to a special wave length as is the IBC. The energy influx required to produce visible aurora has been measured (McIlwain, 1960; O'Brien and Taylor, 1964) and has also been computed from optical emissions (Omholt, 1959; Chamberlain, 1961). The results show reasonable agreement. 0.Z - I% of the input energy seems

to be

produce

converted

an

Hultqvist,

IBC

to visible

I aurora

1964c).

light.

is of the

The

order

Measurements

1964).

cylinder in the

average

density

of the

to the

upper

some

15%

of the

solar

beam

auroral

zones

1961;

drag

temperature

in the

auroral

equator

on

1964).

The

heating

auroral

zones

rienced

during

geomagnetically to be

these

and

4 or

It has

with been

emissions

of intensity

to include

emissions

fairly

Injun zone

the

be

energy

occasions much

radiated

energy

away

(only

1961).

It

atmosphere

particle

3 indicate

influx

that the

is essentially days

the

(Jacchia

and

perturbations

greater

in low

in (Bates,

than

the

upper same

as

Slowley, in the

heating

expe-

latitudes.

of Aurora

intensity

at least weaker

on

5 times

Classification

some

upper

the

geomagnetic

perturbations

In connection

by

disturbed

accompanying

seems

on

an

flux must and

contribute

of the

Thus

auroras

energy

thus

a

1963).

of the

at the

within

to Chamberlain,

determined

Maeda,

show

to be transformed

particles,

events

temperature

is primarily

e.g.

ergs/sec.

strong

unsufficient

according

that the

has

of this is probably

observations

atmosphere

Definition

auroral

wind

very

solar-plasma

be

to

(see

3 satellite

of 1020

energy

during

even

Most

Chamberlain,

considered.

may

solar

order

of precipitated

to heat

possible

Injun

of the

wind

relevant

Large

transformed

quite

solar

energy

1963).

flux

required 2 sec

to sustain auroras around (i011 watts) (O'Brien and

is of the

However,

atmosphere.

Recent

Z.

radii

of the

into kinetic

(Mogilevskiy,

1960b;

i%

fraction

converted

energy

earth

precipitation.

appreciable

the

average I0

about

into particle

seems

The

of radius

energy ergs/cm

by meansofthe

that the average energy input rate required the world is of the order of 1018 ergs/sec Taylor,

input

of a few

the

common a few

than

definition to mean

times

that.

4

the

From

of aurora by

aurora

airglow a physical

has

to be

sporadic

intensity point

but not of view

this is not a good definition. nisms of which are different, brightne ss.

Airglow and aurora, the production mechamay well be thought of as being of similar

A definition based on the mechanism of excitation would certainly be preferred. Along this line aurora

is often

defined

as

3914

nitrogen

emissions

band

in which

- which

the

intensity

is produced

by

collision

line at 5577 A is of the order less than unity. Unfortunately, are

complex

them

and

and

Roach

location phenomena subvisual Roach,

of which

of widely

geomagnetic

emissions,

different field.

Roach

the geographical

the geomagnetic

field.

include the stable red arcs, which in middle latitudes (see the review

auroral

(m

arcs),

by particles

aurora

is an

that occur

can

to Elvey,

extremely be

!.

Polar

Discrete

polar aurora

3.

High

Intermediate M-arcs

6.

Ordinary

red

polar

to several

type

of aurora

whole

cap

known

whether

they

or not.

phenomenon.

in the following

The

various

six classes,

for

instance

auroras

(St6rmer's

red

glow

arcs

i00

Mev,

discrete different

from

type

type

in the

give

rise

If)

I)

by

Sandford

energy to polar

cap

and has

a pronounced

activity

maximum.

The

and

cap

is often

auroras

ordinary

(1961b).

range

rare

caps

polar

III)

discovered

protons

which

fairly

at solar polar

was

solar

is thus

type

(St6rmer's

(St6rmer's

aurora

same

frequency

The

energy)

complex

grouped

displays

the

Mev

quite

it is not

low

glow

4. 5.

the

which

all emissions

1964)

2.

by

for

(of very

aurora

and

or the other by particles of energy well include the above mentioned medium-

arcs

as

The

are mostly by Roach

review

red

consider

to use

in one way we will also

The

are

by

it impractical

to be

the as

atom

will in this

produced

over

aurora

the oxygen

We

The

rence

defined

makes

seems

aurora:

is determined

then also and located

produced

types

have

for

- and

_

In airglow it is usually much the excitation mechanisn_s

which

parameter and

the

are produced thermal and

latitude are

(1963)

1963).

which above

One

for airglow

between

excitation

of unity. however,

not well-known,

in definitions.

importance

(due

are

ratio

and emission

glow

from

It is some

i0

absorption. maximum

This of occur-

is distributed

subvisual.

have

several

auroral-zone

characteristics aurora

(St_rrner's

which type

I).

Their

occurrence

and

they

frequency

also

spectrum

show

is,

however,

Class No. latitudes butit

The

arcs

The

average

the values

for

ordinary

from

name).

The

For

so-called type

them.

Notonly

takes

place

and

Such

3.

we

in the

zones The

mostly

slowly

"band." a great and

then

so

begin from

its regular are

very

" waving

irregular

forms

therespectro-

the most

deal

mainly

emission

and

with

also 1961)

Pope,

and

1960,

1960).

auroral

phenomena

also

the

effect

UHF

on

not

so-called

radio

the propagation

frequency

ranges,

with

of a special

the

by

the

excitation.

type.

enormous

variety

in their

talk

typical

sequences

about

with

1963d). a glow

relatively Suddenly across bow

long,

the

shape the band

like a curtain may

but

to the

of light

south.

to appear

to

is between

Chamberlain,

the horizon

bows

or

aurora

but

Akasofu,

remain

north

to lose

"drapery,

may

begin

If the rays

fading

however,

rises

by far,

simultaneously

an

1954, may

due

Display

show

can,

grey

aurora;

will

the

echoes

in low

prominent

Murcray

and

look

review

radiation refers

The

type

(which

Helliwell,

among

produced

displays

"arc"

"rays"

to fold and

and

homogeneous

towards

and

1958,

Martin

high

displays.

red

most

are,

the

at

(1955).

instance

Hartz,

to radio

Heppner,

glow An

by

for

in the VHF

the display

quiet

there

and

rise

One

horizon.

ing

(see

of an Auroral

auroral

(see e.g.

east-west.

of this

atmosphere gives

is the

displays

rest

km

high

StSrmer

auroral

radio-aurora

ral development.

and

line see

will include

Development

auroral

_

often

is 196 and

the

(cf e.g.

especially

ionization

events

then activity.

auroral

They

limit

light is emitted

1961,

term

The

activity

magnetic

ordinary

displays

of electromagnetic

The

The

solar

rare.

height

6300

and

visual

waves,

ionization

of

very

details

in the ultraviolet

emissions

aurora.

red

ordinary

Peterson

of radio

low with

that

auroral

of aurora

In this review only

are

more

at radio-frequencies Egan

to

lower

The

feature.

common

at

3 - high red aurora - is the most common also occurs in the auroral zone sometimes.

intermediate

their

higher correlation

similar

faintness.

scopic

is

a negative

appear

and

the

forms

it may arc. and

one

for

arc

to form

assumes sky.

disappear

an

or more

approximately hours,

brighten The

of of the

poleward

oriented

quiescent

in the and

Equatorward

along

(arc),

tempo-

drift-

here is then

and likely

irregular

the appearance Rapidly all over

of

moving the

sky.

As the display dies down, waves of light may surge upwards from the horizon in quick succession causing existing auroral forms to brighten as the waves pass over them (flaming aurora). A continuous glow (veil) may extend over a large part of the sky, serving sometimes as a background to the active forms. At other times, diffuse patches of light, closely may

resembling

come

There

and

is a tendency

phase.

The

of the

and

This

Auroral

Union

St6rmer

and

The

Committee

of the scheme

i.

ous

b) and

for

arch

are

to be

forms

i.i. Band-like border.

(Fig. an

I.i) arc

These

3.

sets

diffuse with

surface

sequence On

the

is poleward

the development For

instance

some

in.

the details

is quite

good

Stormer

descrip-

(1955).

or folds

These

are

or part

recommendations

described

in detail

"International

for Jacka

have mostly been classiof 1930 of the International

Quiet

Sun

Year"

de G_ophysique" describing and

in terms

worked

in his book

(IQSY),

(CIG)

auroras.

Paton

were

also

has

It will

(Fig.

1964-

adopted be

briefly

(1963).

of 4 parameters

(6 if brightness

included).

are

divided

forms:

into three

These

the form of an

arch,

are

appears with

groups

characterized

as

a simple,

a regular

lower

by

a continu-

slightly border

curving it is

(A).

(ii) When kinks

the

following

(i) When called

the

described

caps

see for

International

is described

also

Auroral

lower

polar

sky.

mentioned.

in section

events,

of nomenclature

aurora

color

as

Geophysics.

"Comit_

below,

An and

The

auroral

discussed

after

correlated

disturbance. zone,

in the

until twilight

into arcs is closely

decades the auroral forms with the recommendations

(1930a,

1955).

reviewed

there

Forms

(StSrmer,

new

and

pulsations,

the central

auroral

of Geodesy

1965,

over

will be

In the last few fied in accordance

.out by

pattern

of the

of individual

here

regular

reformation

magnetic

especially

different. tions

for

equatorward

side,

appear

with

development

coincident

typical

4.

clouds,

go,often

the lower

1.2-) the form

border is called

is irregular a band

(B).

and

contains

a

1.2. or a veil (V).

Diffuse forms:

These may take the form of a patch (P)

(i) The patch is simply a blob of illumination boundary; it often resembles an isolated cloud.

ill-defined

with an

(ii) The veil refers to the uniform luminosity that may cover alarge part of the sky. It may occur alone or as a background to other forms. 1.3. Rays (R): These are shafts of light aligned in the direction of the earth's magnetic field (cf. Fig. 1.3). There may be a single ray, a bundle of rays close together or many scattered rays (subscripts i, Z, 3 may be added to R to indicate short, medium, and long rays respectively). 2. Structure is described by the following

three adjectives

2.1. Homogeneous (H): This term implies an apparent lack of internal structure in the form. The brightness is uniform or it changes only gradually across the form. A homogeneous arc (HA), and horseshoe-shaped bands are shown in Fig. 1.4. 2.Z. Striated (S): The form contains rather irregular striations or filaments aligned roughly parallel with the lower border (Fig. 1.5). Striation is usually recognizable only when the form is nearly overhead. 2.3. Rayed (R): ance within them of rays the

geomagnetic

3. may,

field (Fig.

Qualifying

when

two

numeral

closely

3.Z. of an arc

or

be

Multiple

associated

script

and

situated

One

This

of three

term

parallel actual

homogeneous

Fragmentary

along

the

by the appear-

lines

of force

of

qualifying

parameters

to the description.

roughly the

aligned

1.6).

added

(m):

indicates

band

are

parameters:

relevant,

3.1. more

Rayed forms are characterized which

is used forms

number

when

of the

there same

of forms,

occur kind.

e.g.

two (A

m2HB

subsignifies

bands).

(f): This

is present.

8

term

is used

when

only

or

a portion

3.3. tion

Coronal

of the lines

geneous they

forms

pass 4.

(c):

of magnetic may

over

When

also

the

force

present

magnetic

Condition

any

rayed

form

the rays a similar

is

viewed

in

appear

to converge.

coronal

appearance

the

direcHomo-

where

zenith.

describes

the

behavior

of

a form

or

of

the

whole

display.

4.1. in

Quiet

position

or

4.Z.

(a):

forms

are

Such

along

(i) boundary

(ii) border the

of

of

form

undergoes

a form

which

only

very

slow

changes

a form

is

frequently

a 1 of

- refers a band.

to

a 2

-

to

while

refers the

the

or

movement

the

form

moves

changes

its

shape

bright.

rapid

itself

of

folds

change

may

also

of

or

irregularities

shape

move

of

the

rapidly

lower

across

sky.

(iii) horizontally

rays

fade

rather

other

parts

often

ation

a 3

- indicates along a form.

(iv) quickly,

a 4

of

sky.

the

4.3. and

range

a large

ing

upwards

very

rapid by

flickering

(p):

from

in

to

this in

a fraction

Pl

a variation forms.

the

occurrence

a display similar or

A photograph

fluctuation

(i)

over

- refers while new,

Pulsing

rythmic

may

display out the

up

The

Active

rapidly.

the

(q):

shape.

-

pulsating

of

an

a second

forms: the

event

The to

is

The phase

of period

the

which

seen

in

rapid

of

fluctu-

of

the

minutes.

form is

Fig.

fairly

order

affected of

movement

in which forms forms appear in

a condition

brightness.

brightness,

a rapid

as a whole different

such

describes of

of

or

uniform

forms through-

(ii) area

P2 - flaming aurora. This kind of pulsing extends of the sky which appears lit by surges of light sweep-

over

it.

and

(iii) P3 more or flames.

flickering: less irregular This

A large part changes

occurs

only

9

rarely.

of in

the display brightness

as

undergoes if lit

1.7.

(iv)

P4 -

that progresses

rapidly

Most

can

or

auroras

sometimes (f)

' are form

ness see

by in

and

color

Jacka

and

very

during reported arcs zenithal

an average was found

.other

hand,

be

or

as

narrow

is

greater

at

acitivity

Roach,

symbols-

of

medium

length

for

the

form

(as) the bright-

(for

details

the

m

was

a few

a

solar

cycle

and

again, have

It

has

been

(Elvey,

1957).

been

measured diurnal

of

found

to

the

arcs

vary

with

atmospheric When

auroras

often

extension

to

heights-the

red

discovered

thickthe

On

significant

the

great

km

The

has

No

of

18.2

1963). activity.

extension

and

the

thickness

and

thickness

smaller

cameras,

the

3.5

have

values

recording

Volkman, magnetic

vertical

kin.

being

increase

of

aurora km

The of

1961).

The

ten

net

the

(Akasofu,

found.

extension

4000-5000

between

curtain

thinness of

1963).

measurements

(Kim and increasing

auroral

lengths the

varying

characterized

recordings

of of

are

a remarkable

Akasofu,

coverage

km with

150-350

of

arcs

values 9.1

and

photographic

Recent

given

zones

depth

the

appear

sunspot less red

deep auroras

stable

midlatitude

may

occur

in complete

arcs,

by

auroral arcs. and in height. rings

around

They Present

Barbier

(1958),

cover some evidence

the world

hunsuggests

(cf. Roach

and

1963).

The

rays

are

characterized

length has been extensively to several hundred krn, but

found

are

auroral

1962,

completely from ordinary of kilometers in latitude

that they

150

four

a S cfR2Bsignifies

rays

direction

auroral

active

end to

instance

symbol

the

the

longer.

an

at

al.,

by

have

the the

by

forms.

A.

The differ dreds

east-west

et

still

atmosphere

of type

in

generally

starts

the

bands

limited

as

activity,

the

From

variation

bands

solar

For

after

and

value of to increase

for

seasonal

and

in

be

described

whose

of brightness

of homogenous

a horizontal direction along the form magnetic zenith. Symbols indicating

continuous

arcs

variation

extent

1963).

extension

may

well

(R2B)

added

arcs

were

so

be

(Feldstein

mentioned 40

in the

Paton,

IGY

fairly

band

direction.

been

irregular

horizontal

subindices.

may

long

An

the

be

a rayed

auroral

made

to

of

north-south

with ness

thus

moving rapidly a corona in

The

along

five-with

a fragment (R2) and

streaming:

kin.

Especially

to extend

of the order

up

the to ii00

of 1 krn (see

by

studied a more

sunlit km e.g.

rays

great

and

thinness.

The

by St_rmer (1955). It may amount common value is between i00 and can

sometimes. the

length

recent

I0

be

very The study

long

and

diameter of Akasofu,

have

been

of the

rays

1963b).

is

Wilcke mately (1920)

(1777)

along found

first

the that

noticed

that

great

to be

due

to the

would have to be at about StSrmer (1938) found the sky.

Abbott

(1958)

disturbed

7 or

8 ° lower

rays

field

showed

than

the

of the

a rate

aligned

approxi-

Vegard and Krogness point," i.e. the point

field

1000 km to show a one auroral zenith to wander

measured

are

appear to converge, the magnetic zenith.

curvature

at least 1° in 5 minutes of time. side of the normal (undisturbed) the

auroral

earth's magnetic field lines. the elevation of the "radiant

towards which the rays in a corona cally one degree or so lower than is too

the

of motion

is systematiThis difference

lines.

(The

degree around

for

the

rays

displacement). a little in the

radiant

point

The radiant point was found on magnetic zenith, but measurements

that

the

radiant

instantaneous

point.

No

magnetic

relationship

of either of

zenith

between

was the

motions

of the magnetic zenith and the auroral zenith was found. Cole (1963) has studied in detail the geometry of the radiant point and found that commonly him

as

differs the

by

0.5

direction

a straight amount

line, passing to as much as

auroral oriented

zenith along

about

at auroral in other

heights, ways.

Detailed forms

auroral

normally Dark about the

the

studies seen

detailed

direction

is

have rayed

There

is

in time.

Rapid

observed Campbell

and and

(1962),

shown to the

teristics berlain

a more of various (1961).

a segment

difference of the

with

width They

(Nadubovich

is several

in aurora in auroral

detailed auroral

Berger review forms,

field

accuracy

exist not only but also in what and

only

emission

(1963),

see

11

lines

Starkov,

in is

1961). length often

of in

often

also

minutes.

not

of older

of

rays are valuable

of 150 m and an average have been observed most

Campbell (1960a,b), (1961), Iyengar and

(1962),

the give

by

may local

comparable

that fine structures eye or the camera

duration

variations by

defined

as

geomagnetic

to obtain

forms

structure

studied Leinbach

Skrynnikov For

The

a fine

zenith,"

regarded

of the

difficult

homogeneous

hours.

auroral

ray,

the observer. The degrees. Observations

filaments of a minimum Z0 km have been found. morning

"local

yet been reported. Presuming lines such observations would

which

called

the

through several

have not the field

information

° from

of a (hypothetical)

it

and

in space rate

recently

Campbell and Shepherd(1961), Gustafsson

investigations e.g.

have

but

StSrmer

been

Rees (1961, Omholt (1964).

of the (1955)

characand

Chain=

5.

Emission

Spectrum

But will not be Bates

for

a very

dealt

with

(1960)

The colour

and

brief

introductory

in this review.

Chamberlain

aurora

seen

survey,

For

the

auroral

a detailed

spectrum

review

see

e.g.

(1961).

in high

is due to a forbidden

latitudes

is usually

transitition

(_S_°D)

green

to the

in the

oxygen

eye.

The

atom.

O

The the

wavelength eye.

time

is 5577A,

The

of the

excited

In lower

nomenclature

6364,

6391

5577Aline.

excited

level

of about

in active

the excitation

There exist emission.

1958.

6300

sec for

Most

and

to be

red

forbidden

with

1960).

Due

1955).

(high

red

is then

in cascade

aurora

the

(ID---3P)

a lifetime

6300,

after

of the

to the long

it is therefore

of

to a life-

Harang,

characteristic

this line and

as

lifetime,

mostly

seen

these

lines

are

emitted

for

some

time

ceased.

auroras even One famous

other

seen

is produced

(Omholt,

sensitivity

corresponding

The long lives of the metastable levels 6300A lines are emitted give rise to colour

auroras

auroral

the boundaries

maximum

low

(Omholt

spectral

which

line is also

if0

has

sec

is often

The

of O,

to the

is very 3/4

aurora

at high altitudes. the k 5577A and_

variations

which

the

is important

in auroras from which

6300A

of about

used). The

deactivation

after

level

A triplett

is close

probability

latitudes

in the the

which

transition

in high example

spectra

are,

latitudes with anomalously increased of this was the one on II Feb.

belong

however,

to one

not

very

of three

sharp

types,

between

(Krasovskii,

1961).

The first type is the low-latitude spectrum mentioned above, in which the ratio of the intensities of the 6300A and 5577 A lines is high, and where

these

two

molecule

bands.

dominate

but

cules

are

emissions In the next

in addition

seen.

This

latitudes.

Finally,

molecular

bands.

of atomic systems most

oxygen

frequently are

exciting

agent

to the third

type,

emissions

type

type

appears

apparently into the

in high

atmosphere,

e.g.

and

and

is characterized

second

latitudes. for

by

the

type.

IZ

This

The the

depth

and

high

the

type

from

low

intense line

band of spectrum

between

of penetration

increasing

moleand

green

negative

third

difference

depth

atoms

nitrogen

numerous

spectra

positive

detail.

ionized

in both by

in such

the nitrogen

neutral

is observed

in great

accounted

over

of neutral

that

the first and

correlated

lines

of spectrum

the third

and

dominate of ionized

It is remarkable

ofN 2 are

spectra

strongly

the of the

the first

Auroras located at great atmospheric depths usually have a red lower border (red aurora of type B). This is due mainly to the first positive bandsystem of the neutral nitrogen molecule. The reason for the domination of the N2 emissions at great depths is probably that the 'S level

of Ol

The

is deactivated

sunlit

auroras

auroras

located

color

which

by

have

in the

dark

is produced

by

collisions

to

a spectrum

an

appreciable

different

atmosphere.

They

re.sonance

from

have

emission

amount.

that of the

a bluish-white

of primarily

the first +

negative

Of

band-system

special

first found

by

that protons 4000

interest Vegard

are

km/sec

forms.

entering

appearance

others).

Auroras

impact

certain

at least

one

aurora,

for which

alone

{Omholt

more are

is often

(Stoffregen

and

Chamberlain

seen

field.

stable

feature

location

than

of these

They

are

196Z).

For

arcs

namely

red

the

details

and

Galperin

arcs,

6300

_

mentioned line has

is definitely

lined

up

along

tion without

any

low

energy

(1964),

spectroscopic

the excitation

particles.

On

the

may

be

how

the magnetic

Megill

have

proposed

and

Carleton

responsible

excitation

for

mechanisms

(1964)

the excitation. are

reviewed

by

13

Roach

emission A distinct main

the

forms

reviews

no

of

other

identified.

of circles

from

the

along the geomagnetic by collision excitaexcited. effect

According caused

excitation

field control

comes

in.

fields

proposals

Roach

by

is chemical

electric

of other and

It the

the geomagnetic

that local

Anumber

the

clearly by

being

if the

it is difficult to understand

be

been

a heating

hand,

of

(1963).

surface produced

features

other

see

it

contributors.

to the eye. started, on

and

projections

equatorial plane to the earth's It is not clear how they can be

to Dalgarno

case

types

earlier,

controlled

geomagnetic field lines.

other

aurora

more

Krasovskii(1961)

In the midlatitude

The

the proton

been

relatively,

energy

invisible this has

strong

have

After midnight no hydrogen but rather north of these.

between

Derblom,

(1961),

spectroscopic

in other

main

and so

In any

energy

glow is barely visible or even the electron aurora and, when

dark

might

1962).

than

to

preced-

1958,

supplied,

the

up

line was

the protons

certainly

of it before midnight. south of auroral forms

Elvey,

theHa

et al.

were

showed

observed

that this aurora

auroras

of magnitude

They

I ,

in homogeneous

been

and

in which

(N 2

velocities

mostly has

(Romick

emissions

electrons

seen

molecule

line contour with

glow

observed

equator side is observed region

are

auroras

that in those

order

emissions.

atmosphere

They

been

by proton

appears

line

of their

hydrogen

of bright spectral

nitrogen

hydrogen

upper

weak

have

charged

Analysis

1951).

to other

The hydrogen occurs before

the

the

recently,

ing the

produced

are (1939).

(Meinel,

More

compared

of the positively

(1963).

for

may

6.

Methods

of

Recording

Almost by

visual

all data

observers

sky-cameras, was

by

up

(1957)

and

detailed Fig. white

(1947),

Davis

and

the

Studies

During

IGY

net

the whole

sky

a large

(see

have

(1955),

Elvey

been

every

all-

minute, and

(1955),

Stoffregen,

set of allsky-camera

taken

constructed

Stoffregen

and

was

of so called

automatically

allsky-cameras

A

allsky Soviet

Morphological of aurora

Lebedinskii

Elvey

description).

1.8. Most film. The

for

morphology

to IGY.

Various

Gartlein

Aurora

concerning

photographing

in operation.

used

Visual

Park

1957,

for

are

shown

pictures

films taken hitherto have been 16ram and Canadian cameras used, however,

a in

black and 35mm

film. In the last few years and Heiser, 1959; Gadsden,

color film has begun to be used (Sand.ford 1960; Sandford, 1961). The committee for

the

"International

Year,"

the

use

of 35

detailed net

Quiet

mm

synoptic

bilities are

has

devices and

(Elvey

Davis,

and

The

in (b)

The

(c) moving

model

observed,

(1960)

They

and

the

the possi-

IGY

records of the

satellites, auroral

films

have

regions.

been

construc-

1961).

have

made

them

with

arrived

that

solution

altitude

caps

Kaneda,

comparing

the

For

IGY.

regions

from to the

high

polar

aurora.

during

of the polar

very

recommended

desirable

it was

patterns

and

allsky-camera

as in

well)

was

detection very

at

and

eye

more

is

If the

observations in the

that

operated slightly

of

weak

allsky-camera

forms. his

by

than

allsky-camera

Nagata

Leinbach

locating

The

allsky-camera be

US

detecting

accurately

sky,

and

types

observer

equal

analyzing

of the

an

evaluation

of

simultaneous the

all-

visual

following

conclusions,

s.

other

visual

of the

observations.

other (a)

most

by

most

1957;

has

contribution

be given

for

of CIG details it is highly

part

synoptic

may

Belon,

photometric

most

important

observations

among

areas

showing

Deehr,

sky-camera

more

in the future

scale

most

problem

Automatic

large

that for

A

photographs

ted

over

large

1964-65,

provides

denser

shown

limited.

morphology taking

will be

of obtaining

very

which

studies

of cameras

Experience

Sun

film,

very

but

less weak

well

able

to

observer

see were

would,

in

small

region.

allsky-camera

shape

the to

general,

is

14

forms

to the

and

visual

of most

details

of

watch

only

be

superior

However,

if

superior

(and an

probably

experienced is

about

forms.

superior the

IGY than

diffused

defined

is much recording

during sensitive

in

the

observer

auroral

very a

bright small to

the

sense

or part

those

entire

(b)

fastof

of sky

of

in

forms.

the

the is

above.

to

(d) A greater degree of continuity in auroral forms is often indicated in the compressed image of the sky on all-sky photographs than is apparent to the visual observer. (e) During the times when visual observers report pulsating aurora, the over-all appearance of the display seems to be quite distinctive and often readily identified on the allsky film. The around

exposure

Z0

possible

to

studies

of

than

has

time

sec.

By

take two

to

earlier was

used

(Davis

and

Hicks,

It

has

recently

three

the of

auroral

aurora

(Noxon,

of

means

pictures orders

been

ordinary

intensifier Z4

of

possible.

successfully

allsky-cameras

image

times

for

TV

a second.

magnitude An

is and

Such

more

instrument

the first time

generally

camera

rapid for

time

rapid

in the

it films

variations

filming

autumn

is allow

of of 1963

1963).

become

possible

to

1963).

15

observe

visual

aurora

in

daytime

Figure Fig.

l.l-Auroral

Fig.

1.2-A

Fig.

1.3-Auroral

Captions

arc

band

rays

Z4 pictures

photographed per

Fig.

1.4-Homogeneous

Fig.

1.5-Striated

Fig.

1.6-Rayed

Fig.

1.7-Photograph

sec.

with (Courtesy

auroral auroral

arc

and

an

exposure

time

T.

N.

and

Davis

of

1/60

G.

T.

sec, Hicks).

bands

arc

bands

rapidly

of an

and

new

active forms

aurora. appear

The

forms

move

continuously

and

in other

fade

parts

of

the sky.

Fig.

1.8-Allsky

camera

(Courtesy

Comment: tional

Atlas

Geodetic

Atlas," Year -

"Physics

and

prepared of

the of

to

Figs.

of

Auroral

by

the

at

Kiruna

and

4-7

Forms,

on

Z9

Jan.

Committee

Z, and

4,

Oslo

for de

and

6

airglow."

16

-

can

be

taken

" published

Union,

International Figs.

aurora

1-Z

Geophysical

"Comit_

concerning

taken

1957

Stoffregen)

Alternatives

"Photographic

or

pictures

W.

the

1957

or

International

G_ophysique," from

from

by

Chamberlain's

either

the the

Interna"Auroral Quiet

Edinburgh book

Sun 1963.

~

~~

F i g . 1.1 - A u r o r a l a r c

Fig. 1 .2 -A band

Fig. 1.3-Auroral rays photographed with an exposure time of 1 / 6 0 s e c , 2 4 pictures per sec. (Courtesy T. N. Davis and G. T . Hicks).

Fig. 1.4-Homogeneous a u r o r a l a r c and bands

F i g . 1.5-Striated a u r o r a l a r c

Fig. 1.6 -Rayed bands

F i g . 1.7-Photograph of a n active a u r o r a . The f o r m s move and fade rapidly and n e w forms appear continuously in other p a r t s of the sky.

2.

I.

Geographical (a)

poles

The

Distribution

the

auroral

seems

Loomis

on

(1860,

aurora

Fritz's

the night

in USA

originating

at any

was

maximal.

geographical

equal

of night

It has

statistical

as

has

become

having

review, is

equaled

of

a particular

the

or

use

the

distance

zone

over about from

will of

a period variation one

night

to

by

between of be

overhead

the

several

of

the

to

as

points

that

as

months.

location as

of is

at

the

often

17

this

auroral done

isoau-

the

auroral

zone

width. the

there by

the

through literature.

the is

peak

of

max-

observations

definition zone

in

this zone

amplitude of

which

In

auroral

position

determined

With

points

called

half-maximum

The

position

(1953)

are

of of

of

is thus

in evaluating

variable,

of

zone

connecting

width

of

curve part

Chapman

zenith

think

and the

activity.

auroras,

of

another,

years which

auroral

taken

"Lines

the part

The in any

auroral by

in the

of the

any

overhead

of

from

where

width.

The

1881) amount

1878,

during

aurora

aurora

unspecified

definition

no

studied

1874,

of points

recommended

recent

was

location

sky

of seeing

curves.

(1837).

to about

of the

of the

towards

of a large

the locus

part

occurrence

generally

the

measure

occurrence

taken talk

to

auroral

imum

but

will

1873,

up

map

of seeing

in

(1868,

isochasm.

distribution

customary

a finite, we

an

Muncke latitude

analysis

a line, having

been

the probability

by on

times

as

probability

is called

first

Fritz

old

in any

of equal probability of auroral total lines or isoaurores.

It

by

defined

It is thus

with

to use

and

very

aurora

continuously

frequency

the first detailed

isochasm.

others

in print

from

an

the maximum

increase

a detailed

zone

time

not

made

auroral

points

does

noted

of seeing was

connecting

and

Aurora

Activity

occurrence

(1881)

could delineate auroral zone.

probability

sky

1868)

Fritz

which he northern

been

of auroral

in Germany. data

of Auroral

activity

to have

dependence

by

of Visual

Introduction

That the

Morphology

we

cannot one

night One

is

then

using

the

notation

auroral

zone

for

at a given moment of time. Below, "zone" or "momentaneous auroral this unique-time Both highly

the width

dependent

commonly

account

in this measure. defined

each

similar

determined

a

1 ° latitude

following

is widely

geomagnetic

and

S.

the

The

are

on

the

regions,

called

(b)

the

{1944)

modification

termined taken

by

at 39 Arctic

during

While tematic about

1878,

particularly delineations, periods

zone

of it are

shown

the

is not

employed

taken

auroral

borders

appear-

borders

at 5-minute

station.

It gives

auroral

and

south)

belt

auroral

side

(Jacka

suggested

and

subauroral

auroral

polar

belts

zones

zones

zones

and

from

45 ° N

and

the

au-

Alternatively, are

named

cover

Paton,

Chap-

between

between

zones).

which

by

extend

the

cispolar

cap,

1963).

latitudinal

activity

delineation

of Fritz

(1881)

in Fig.

2. 1 together

basis

of photographic

on the

and

the

of the

auroral

auroral

visual

zone

observations

Vestine

had

those from however,

of time

most activity,

observations

with

made

and

Vestine's

a zone

de-

recordings at three

sites

1957-58.

Fritz's

auroral

of the

(1960)

{north

auroral

regions

stations

the IGY,

is

(or full-hour) total number of

lower

the

the

the

auroral

Feldstein

also

the minauroral

include

on

of visual

northern

The

aurora

lower

zone

of auroral

geography,

regions

and

side

those

locations

the through

auroral

within

transauroral

a,b)

to the poles;

regions

equatorial

distribution

The

on

auroral

regions

while

Observed

counting

or for

distributions.

(_m) 60°

auroral

of the

of auroral

passing

latitude;

(the polar

regions

auroral

by

The

latitudes

caps

{1962

terminology

used.

60 ° magnetic

450

Davis

band

sharper

45 ° and

roral

employed.

frequency

intensity

the total number

but somewhat

The man,

by

hour-as

intervals-in

of the auroral

of activity-measure

The

exists

activity.

center

is the occurrence

intervals.

aurora

precipitation area" zone" will be used

auroral

of the

in which

as the ratio of the number of half-hour aurora could be seen overhead to the

full-) hour

incidence,

of visual

type

area

"auroral occurrence

the location

measure

defined in which

half-(or

ing

and

on the

used

generally intervals

into

distribution

the

with

at his

was

from

based

almost

several

disposal

more

hundred

entirely

on unsys-

years

systematic

B.C.

up

observations,

the two polar years 188Z-3 and 1932-3. are based on material obtained over very

secularly

changing

18

geomagnetic

to

field,

varying

Both long solar

activity,

partly unknown meteorological

Feldstein's curve is based the use of a fairly uniform employed used, as

conditions,

etc.

In contrast,

on observations made within a few years with technique at all stations. The auroral indices

in his determination are more accurate than those only the aurora in the zenith has been utilized.

The

greatest

auroral

zones

Feldstein's

The

difference

is in the

curve

first

between

region

reaches

attempt

Vestine's

of Hudson

about

Bay,

4 ° farther

to investigate

and

Feldstein's

in North

south

northern

America,

than

the auroral

previously

where

Vestine's.

statistics

in the

southern

hemisphere was made by Boller (1898). White and Geddes (1939) estimated the location of the zone on the basis of scattered visual observations

of aurora

based are

on

australis,

geomagnetic

shown

and

Vestine

observations

in Fig.

2.2

together

with

Feldstein's (1960) zones. The at 20 stations on the Antarctic

and

Snyder

Bond's

and

IGY material continent and

recent

rence

study

frequency

in time

to the

auroral

forms,

ords

taken

and

of the detailed

is that of Davis solar

activity

as defined

in Alaska

in northern

Canada incidence

in connecting stations.

the

The tude

curve

latitude. The

The

hourly

tween imum.

60

data

width for

occurrence and

Already

auroral

and

Solomatina

the

zenith

atom=

zone,

during

with

IGY

zone,

was

by

55%

spread

above,

of rec-

than for

69 ° ) the points involved

Canadian

(1962

on

Fig.

of auroral

inner

bemax-

side

of

Feldstein

occurrence

quiet index with

one.

activity

the

2.3).

6 ° in

a) to be

at solar

to I0%0, while

on magnetically

lati-

is about

is a relative

Davis

latitude

on disturbed days in the auroral zones. The the ratio of the number of half-hour intervals

19

It refers

allsky-camera

2.3

(c.f.

occur-

67 ° geomagnetic

defined

that the frequency about

2.3.

to the ,.uncertainty

in Fig.

slower

was taken islands

"incidence"

era' less

66 ° and as

and

evaluation

of the high-latitude

found

down

was

The

from

zones

of auroral

in Fig.

indicated

is due

66 ° geomagnetic

60 ° it was

was

The

between

frequency

found

shown

latitude,

those

in the

1957-58.

a zone

two

(1960)

variation

deduced

"incidence"

the decrease

(1963)

was

latitude

of the

the

70%0 at about

the

90% was

scale

in

(for Cm > 69°).

its maximum

The

b),

geomagnetic

at high

Alaskan

has

in Alaska.

above,

(for the

representing

(1962

Jacka's

employed

latitudinal

maximum

defined

These

used by Feldstein at two stations on

situated south of Australia. The technique was similar to that used in the Arctic.

A

(1945)

in the Antarctic.

days

and

in about

of activity used auroras in the

zenith

to the total number

corded

in the form

found

that the

auroral

auroral

While

Jacka

of aurora points

at College

tween

the general

conjugate

area

between good

auroral

in USA,

detailed

Island

in the

northern

conjugate DeWitt

areas.

was

quoted

usually

certainly

above.

occur

as has

long

as

and

pairs

suspected.

for

at either

More

Island

and

the

observed of luminos-

and

and

MacQuaire

Kozebue

to be

of the

in the

simultaneous points

other

probable

end

be-

station

(1962)

observation

most

conjugate

correlation

of variation

found

any

therefore

occurrence

nearly

DeWitt

at Farewell was

years consistant.

(if at all significant)

and

of the

than

are

Antarctic

areas,

motion

auroras

better

It seems

austral

between

not the

reported

at Campbell

conjugacy

conjugate

been

and

observed

The

which

correlation

in the two

of the

however,

at Ellsworth

hemisphere

Breakup

realso

and

relations

between

(1960)

small

of form

events

southern

one.

Island,

activity

correlation auroral

boreal

in the last few

are,

correlation

Fillius

but very

pictures

but

They

any

and

in the

the detailed

hemispheres,

MacQuaire

kin),

the detailed

ity between

tions

and

600-700

about

appeared.

did not find

as

investigators

same.

ICY

in the two

of observation,

last mentioned occurrence

the

before

this have

(1961)

(off by

closely

known

on

intervals

The

of auroral

very

phenomena results

by

are

was

some

the

probability

zones

Nothing

of half-hour

of ascaplots.

two

investiga-

that auroras

of geomagnetic

observational

in

employed

data

field lines,

would

be

of great

value.

The

occurrence

tropical)

of aurora

is extremely

rare.

in very Even

low

latitudes

in central

(subtropical

Europe

and

the probability of seeing aurora is only a few thousandths center of the auroral zone. instead, these medium and auroras recorded tions by

of auroras

Schove

auroras by

are generally very spectacular also in ancient times. Recent extending

(1955),

Chapman

(c)

1957

are

(1956) low

and

latitudes

c), Abbott

(1951),

and

have

(1957

been

USA

of that at the low latitude

often been noted and of older observa-

region

Chapman have

southern

been

a, b).

described

Abbott

and

made Several

rather

of observational curves

good

equatorial

reasons plane

for

auroral

zones

postulating

outside

the

ZO

earth's

with

circular surface

fully

Chapman

of red auroral arcs occurring rather regularly will be discussed later in this chapter.

Comparison theoretical

There geomagnetic

at very

(1953,

(1959 a). A type auroral latitudes

into the minauroral

Matsushita

occurring

and have summaries

and

in sub-

various

symmetry of

distance

in

the

parameters representing ables of those processes, associated auroral

with

the

and

range

and

process

earth.

It follows

auroral

seems

physically

of a great

the

and

be

that introduced

field

different

from

the

line which

real

and

in the

According

phere

the

along

only

ion moves

assumption the seems

The along

purposes are used

projections the

real

of circles

geomagnetic the

may

distance

be

plane

same

in the

in one

quite of that

place

as

earth's

hemisphere one

in the

plane

to one

some

surface

founded.

is that an

of the auroral defined No

by

other

at-

will other

electron

hemis-

zones

or

an

along

field lines.

details

in the equatorial were

calculated

plane by

Such

of the actual

experimental

isochasms.

with

the

of Mc!lwain

method

L

curves

consisting

21

of integration

to the

Hultqvist

with

identical

a perturbation

a

earth's

involved.

field lines,

of comparison

practically

on

to be well are

at the

corresponding

in the foregoing

equatorial

an

face

configuration

of the

made

field line or

processes

if the

processes

on

will

field from

equatorial

surface

auroral

time,

field lines.

a geomagnetic assumption

the

the

points

plane.

the

projection

geomagnetic

from

earth's

the

equatorial

to this view to the

physical

the

with

as

of e.g.

the

place

and

lines,

at fixed

near

on

plane

field

If that is so, takes

equato-

meridians

magnetic

even

directions

distance

equatorial

at and

the

influenced

dependence

earth's

plane

the

The

magnetic

regions.

intersection

be

to geomagnetic

be true,

in its outer

intersects

correspond

The

should

field line connecting

mosphere

of the

two

Thus

average

observed

regard

in the equatorial

that of the

same

in the real

is appreciable

here

will not

longitudinal

with

from

disregarded.

locations,

deviation

distorted

the process

dipole

the

said

at which

only

radii

all geomagnetic

by the

the

of the different

in the

processes

auroral

deviation

been

is heavily

the

from

near

contribution

symmetric.

plane

are

seen

connected

distributed

by

This

has

time

many

equally

dipole field. surface.

What

are

earth

effects

axes

be

plausible-the

averages earth

rotation

that-if

zones

of several

minor

will therefore geomagnetic

in or

a measurable

equatorial

provided the

phenomena

field is circularly

geomagnetic

rotation,

at a given

in the

at a distance the dipole

in the

geomagnetic

plane

the dipole

plane

earth's

of the

the

field affords

surface,

configuration

rial

of auroral

Only

equatorial

earth's

by

the occurrence

zones.

in the

statistical averages for corresponding variin and near the equatorial plane, which are

The

earth's (1958)

projections

{1961). along

surfor

Hultqvist

the dipole

line

of the deflection line due to the harmonic

from effect

a dipole field line of the higher of the second to the fifth terms

development

yielded

deflection

of the vectors

for

gave the deflection for the mation field line-coinciding torial

plane

from

the The

well

outside

a large

earth's

point

calculations

were

of 15 geomagnetic results of Vestine's

netic then

field for available,

epoch were

spond to the two of 7. 13 and 5.60 lines

are

Vestine

the

circles earth

geomagnetic

Since

which the

of the

order

of

in latitude best

the the

1 ° in latitude.

The

the

geomagnetic

calculated

ZZ

data

were

in Fig. They

Z. 4 corre-

having radii the dipole

auroral zone of over the North

extended about 4 ° farther as presented by Feldstein agreement of circles is zone

to about in and

one near

and

data

used

between good. that

degree. the

northern

IGY, it seems probable determined auroral zone

with

accord

northern except

may account for minor It is probable, however,

plane.

for

Z5 ° respectively.

Feldstein's

full

configurational

which

plane along

ZZ ° and

degree of latitude. is, within the limits

equatorial

for

equatorial projections

error also is less than one IGY northern auroral zone the

itself.

longitudes

are shown hemisphere).

stations

1945, which of 1957-58.

surface line

less than 30 degrees. of the earth's mag-

epoch

to it amounts

the

earth's dipole

configurational projections

between

dense during experimentally

These

circles are ovals with the longcontaining the 170 ° and 350 °

circles

of observation

quite of the

lations are for epoch with the observations

of them analysis

the calculated curve one. The IGY data that and

lines.

equidistant

out that the experimental with the circle projections

network

zone was in location

plane plane

colatitude

conforms

auroral error

36

in the geomagnetic radii, for which the

difference

projection

the

Two circle projections and Fig. Z. 5 (southern

continent, where the observational

maximal

for

calculations

of the higher approxidipole line in the equaof the

the most recent in the computation.

and illustrated in Fig. 4 show the IGY northern auroral zone The

out

The

of dipole

surface-and

carried

1945, used

Hultqvist pointed accorded well

American south than

number

colatitudes, most et al. harmonic

meridians. hemisphere)

field.

of intersection

The projections of equatorial diameter approximately in the

geomagnetic (northern

magnetic

point of intersection with the pertinent the

corresponding

each The

est

earth's

approximation in the spherical

in the

that the is only calcu-

inconsistencies that this

It is thus evident that the of probable error, in projections

of circles

in

Feldstein's Fig.

auroral

Z. 5 together

with

7. 13 earth radii. from the computed the

better

A question

range

the

of interest zone

merely curves.

computations,

of the

computed is

and

one

whether

the

certainly

the

hemisphere

data

partially account for part of the 6 latitude utable

to

errors

especially Dudziak for

or

et

epoch

zone. zone

by

5ensen

observational to the coast

This means were visible

(1960)

Indeed, since have communicated

(point station. Island-is mentioned zone is

15 on

considerable

zone

in the

Fig.

P. 5),

A small shown

over

plausible

in view

circle projections surprising if the agreement

between

error

of MacQuarie

is

one

only

or

the

close

continent. accord

for the northern two hemispheres the

only

this

Arctic. et al. the

fact

that only is primarily

minor

may a minor attrib-

field,

deviations.

region were far inside the occurring elevation,

they

situated auroral

on

in the auroral a circumstance results.

paper, note

Island,

Bond and Jacka that the latitude south

degrees

zone-the No. Z.

the

more

one Taking

than

near this

of

of Australia that

of the

MacQuarie and the above

into account, it would appear that the auroral with the computed curves, with which it shows

Antarctic

of the

two

for

of in the

Vestine's 1945, when

observational

publication of Feldstein's a report in which region

than

or

computations by harmonic coefficients

discrepant continent

in the

and/or used

geomagnetic

show

auroras at low

IGY

one

data data,

Although

numerical spherical

(1962)

part of their auroral in Fig. g. 5 as curve

considerations fairly consistent

agreement

Cain

in effect that the from these stations

implies

auroral

recent of the

to

the

a real

on

it seems likely over the sea of the

in

nearer

between

Antarctic

sparse.

stations in the of the Antarctic

which

the

and

the

analysis

with basis

and

does.

is

were based field for epoch

very

harmonic

as a comparison a1,(1963) on the 1960

All close

were

5.60

much

Feldstein's

discrepancy

for

in

circle where it is (1945) auroral

of circles

the discrepancy, degrees difference

in the

it is

of the observational of the geomagnetic

greater

shown

of radii

° E,

than

projections

to inaccuracy The errors

are

circles

is

differs quite significantly the course of the latter

rest of the longitude Vestine's and Snyder's

As mentioned earlier, the computations harmonic analysis of the geomagnetic southern

hemisphere

of 320 ° E-90

for the In fact,

with

auroral

attributable the computed

southern

projections

longitude continent the sea.

agrees

southern

the

in the

The experimental curve ones. While it follows

geomagnetic

the Antarctic located over zone

zone

two

types

This between

seems

so much

observed

auroral

hemisphere. showed entirely of curves.

23

Indeed, different

the zone

more and

it would be degrees of

Although, postulating the not

as mentioned above, there are good

circular

processes the only

symmetry

in the

producing aurora possible approach.

geomagnetic

in the If e.g.

reasons

equatorial

earth's atmosphere, the drift around

for plane

it is earth

the

for

certainly of the

primary auroral particles in accordance with the adiabatic invariants the determining process for the configuration of auroral occurrence curves, it is perhaps reasonable to expect that the isoaurores should identical with the lines of constant second adiabatic invariant. Vestine and Sibley (1960) with the projected sible

to judge

Sibley also and Leaton adiabatic

computed such equatorial-plane

between

the

calculated, (1957}, the invariant,J

= fll

Figure two other

zones tical

4 and types

are

ray

particles

the two

dipole curves

based

on

d_/v

in the

, has

km in the hemisphere. 5 include, of more

earth's

that

basis.

the

value

and and

Sprague Quenby's

magnetic

comparison, auroral

cut-off

field,

and

of the internal to observed

heights and

(1960), which and Webber's take

from

-15

km

curves zones: the

are almost iden(1959) curves,

rigidities into

field. data as

and

of Finch the second

Their

hemisphere

of vertical

parts closely

15.7.

northern

be

identical not pos-

Vestine

analysis for which

for purposes of or less theoretical

calculations

and non-dipole conforms as

on

are very nearly it is therefore

the spherical harmonic height of electrons

suggested by Gartlein with the isoclines 76 °,

which

They and

approaches

using mirror

range from 57 km to 420 to 633 km in the southern

showing

two

curves. circles

is

for

cosmic

account

both

Neither of these do the circle

projections. What observed

conclusions

isoaurores

can

and

equatorial lines ?

plane Not too

processes and we

are involved. still expect to find

local

However, conditions

into many,

it can close

be

drawn

projections

the earth's in fact, The the

of

would

expect

the

the precipitation rate occurrence of aurora.

the

circles

similarity

in the

between

earth's

geomagnetic

atmosphere along the geomagnetic since no details of the actual physical geomagnetic circular

be concluded to the earth

mirroring of particles Since the

field symmetry

from the probably

average auroral distribution over the drift of the primary particles around tant for the shape of the isoaurores. one

from

height

data play

and therefore mirror height

Z4

can be strongly distorted for the statistical data. presented a negligible

earth's surface. the earth seems If this process to have

field

that for

The adiabatic not to be imporwere important,

a profound on the varies

above role

influence

on

frequence very much

of with

the

longitude

for one

auroral

J = const

occurrence

would

be

expected.

important

in this

primary auroral scale of auroras

There

This respect

other

be

expected

to show

the

average

southern

netic al.

(1960)

with

the

southern

(d)

and

The pendent (1961)

made

Halley roral

distance

obtained

zone

median

south

geomagn,

of

zone

in

1957

Arctic

(1954-55).

was

than

(1962),

the Asian

is

of mag-

e.g.

Gartlein

et

curves

in Fig.

Z. 6

agreement.

The

the

has

solar

been

cycle.

cycle

found

Sheret observations

1956-59.

The

of quiet

to be

and

made

position

arcs,

de-

Thomas

was

at

of the the

au-

following

1

1956

1957

1958

1959

70.8

71.8

71.9

71.0

fat

auroral

Feldstein

mum

One

years.

Year

The

on

zone

observations

Table

maximum

degree

of the

location

years

that may

plane.

by

a good

of the auroral

in the

from

the time

Kp.

activity

analysis

is not

the isoaurores

evaluated

shows

auroral

solar

than

equatorial

comparison 2.4

and

a curve

drift motion

at a definite

been

increasing

of the

of the

Antarctica,

zone,

in the four

A

in Fig. with

a detailed

Bay,

(1963).

of auroral

the phase

such

of the fact that most

than in the

of the aurora have

increase

pole

on

the

because

parameters

curves

projections

Dependence

in intensity

along

That

expected

symmetry

extent Such

extent

points

need a time very much longer to drift around the earth.

statistical

Feldstein

circle

variations

various

observed.

is also

circular

disturbance.

important

for

is not

electrons in order

are

shell,

frequency

thus

before

who

to

after.

compared

at solar He

closer and

the

activity

found

the

pole

This location

maximum

auroral

geomagnetic pole at the minimum These variations in the location

the

at

the

result of

the

(1957-58)

zone

to be

solar-activity

is

2.5

opposite

auroral and

to zone

at solar

-3 ° closer

that in mini-

to the

of the solar cycle than at maximum. are discussed-also in subsection 6 on

motions. (e)

Auroral The

types

and

type

effects

distribution forms

of

of aurora.

auroral Most

activity of

Z5

the

described basic

data

above are

refers

obtained

to from

all

black

and

makes

white

allsky-camera

it impossible

acteristics

as

It is, are

significant

of fairly

to distinguish

well

as

however,

especially

films

between

differences

between

between quiet

of great

rapidly

and

forms.

whether

different

by positive

which char-

auroral

to know

between

caused

times,

spectroscopic varying

interest

in location

exposure

various

and

theoretical

auroras

long

types

negative

there of aurora,

primary

particles. This is because relations-at least qualitative-between the locations of proton and electron precipitation areas is contained in several theoretical models. For instance, it seems difficult to think of electromagnetic

acceleration

are

together

precipitated In fact,

usually before (After but

midnight rather

been

the

auroral

As

mentioned

auroral

(up to forms.

zone

for

58-76

in section The

red arcs, regions.

° N (at

considered

as

be seen 5 degrees et

al.

the

emitting

observed

aurora

south between expect

alone

there

latitudinal

several

distribution

for instance, No detailed as yet. auroral

to be

the pulsating auroral zone.

His shown

auroras This

often

one

or

zones

different

types

a

of

occurrence

prob-

has its maximum in studies of their geo-

of Scandinavia). are

13)

the "proton the isoaurores

Stoffregen (196Z) has forms in the geomagnetic

approximation,

is

auroral

of the

certainly statistical

p.

forms,

There

located

ordinary zones).

are

(see aurora 1963).

of auroral

1 ° wide in latitude) One would therefore aurora"

particles

produced and Galperin, 196Z).

one,

longitude

a rough

in the figure, south of the

investigated latitude

results,

in Fig.

which

Z. 7.

As

he can

occur most frequently some was also found by Heppner

(1952}. The

subauroral auroral of circles (see

is and

negative lines.

Derblom,

"proton

graphical distribution exist the occurrence of different band

line electron 1963,

from the poles than the the electron precipitation

phenomena.

ability for high the subauroral

hydrogen

Stoffregen

and field

side of the of Ore_holt,

emission

of these;

few degrees farther (which certainly are

if positive

geomagnetic

that

equator reviews

no hydrogen

dark region and the main

the

found

on the (cf. the

north

a distinct aurora" and

it has

is located midnight

processes along

low

latitude

red arcs mid-latitude along the

Roach

and

Roach,

aurora

mentioned

above

is

different

from

the

stable

described on p. 10. The red arcs populate subregions with shape very similar to the projections field lines from the equatorial plane, described above 1963).

between the circle projections of radii Z. 5 and 3 earth radii arcs seem not to exist in the

The

regions

have

their

centers

corresponding to equatorial (i. e. L = Z. 5 and 3 respectively). auroral zones. Z6

somewhere plane

circles These

red

There

certainly

exist

still other

tribution of the occurrence aurora inside the auroral guish

it from

eral,

the

fleeting part,

the

than

those

of weak

ture.

seen

Ray

diffuse

bundles

Inner

arcs

are

auroral

Alfv4'n exist

colatitudes number

if

inner

the

and

to

be

firm

80 ° N

geomagnetic

of the

zone,

that

along

a similar

has

by

more in

ray

struc-

arranged

so as

intensity

and

grounds

that

made

this

to

not.

At

against

at

was

determine

from

time,

clear

it

that

the

(which

the

should

geomagnetic

proposal

this

zones

there

ones,

made,

observations

does

not

zone,

is

not

existence

a

seem

if

it

exists,

unexpected

of

the

inner

zones

discussed

the Soviet

Most

data

maximum

data

is geomagnetic.

in magnetic

most

pronounced is a spiral

in a clockwise

of ionospheric

relevant

activity in the

What

is gen75 The

and shape

latitude-time

direction.

Meek

are

exist-

between

summer.

in a circular

disturbances

to the

(1957)

concentrated

spiral.

hand

Lassen

latitude), activity

around

(i.e. from

activity

show

variable

ordinary

It is

unwinding

geomagnetic

change

In genand

consist,

usually with

Since

the main of view).

Nikolskiy,

the maxima

the other

local

in the

he

auroral seen

course

which zone) from

seemed but

to be

Godhavn.

not

only

of disturbance

Z7

evidence

a type

of the morning.

state

at Godhaven

magnetic

observed

is uncorrelated

the planetary

observing

not find any

time,

sky

in the

of aurora

(1959),

instead

the main

significantly

but with

could

but

6 h.

elevation

morning-type

the

or

zones.

zone

south

of

latitude,

found

found

at great

been

is a morning

system,

occurring

have

favor

auroral

found

of high

degrees.

than point

(1963)

of inner

On

are

theoretical

inside

conclusions.

in

erally

coordinate

zone.

that frequently

these

of aurora. The that distin-

in intensity forms

dis-

reviewed.

Nikolskiy ence

on

exist

pronounced theoretical

briefly

auroral

The

or draperies

10

zones

Observations will

and

bands

5 and

draw

the weak

zone.

of bands

zones

of attempts

is much less from Alfv4'n's

auroral

proposed

auroral

possible

outside

relatively

common,

auroral between

large

latitudinal

zones

(1955)

secondary

are

at the

to appear as part of arcs, (cf. Davis, 196Z b).

(f)

at and

forms

seen

in the

frequency for different types zone has several characteristics

aurora

high-latitude

differences

(about for

an

of zenithal

not

to come

produced The

the

too.

inner

aurora up

from

sporadically

elevation

Lassen with

80 °

did

found local

not

that the

magnetic

Analysing

data

obtained in other parts of Greenland and in the northernmost Canada, Lassen concluded that morning aurora of the described kind is observed in the zenith only along a curve coinciding with the projection of the circle with radius 20 earth radii in the geomagnetic equatorial plane (L

= 20) on the

Witham turbance

et

al

surface.

(1960),

for

characteristics.

parameters, of

earth's

an

could

inner

zone

Davis

(196Z

88°),

Alert

instance, They,

not of

reach

high

any

film

b) analyzed

(era = 86°),

The

from

result

diagram

can

of an

critical

Ray

Diurnal

As ation activity

used.

perhaps

on

remains

to

roral

the

be

activity

The

is

most

and

820

there.

Auroral

used

netic

midnight

from These

local midnight being curves demonstrate

lier local curve

time

marked

with 3914.

from

this in the

of a strong

that if there

81 ° latitude of auroral

is an

over

northern

forms

within

Activity

of

depends of

our and

College

occurs

making

recorded.

of stations

It appears

aurora,

considerably

it phase

"incidence,

(68-69°),

the

=

the number frame of

was

indication

(¢

(era= 7_'b)

counting fifteenth

lack

76 ° and

the

on

the

sunspot

knowledge

the

with

the

type

of

cycle. of

the

diurnal

measures

in the

(64-65°),

1 to 2 hours

the

display much

and

still

variation

and after

activity

previous

of

frequency each of the Farewell local

are

au-

latitude. from

Z8

by

(61-62°).

2.8

Murcray

Fig.

of visual aurora Alaskan stations

midnight,

In Fig. data

"occurrence

subsection.

the

largest for Barrow and smallest a shift of the auroral occurrence

It is drawn

of

auroral Very

diurnal

of auroral

" defined

increasing

vari-

measure

complete.

(after Davis, 1962 a) shows the occurrence a latitude belt of width 1 o centered over Barrow

existence

at Thule Lake

the

prevents

distribution

before

widely

is no

of the number

varies

consistent

and

taken Baker

of forms

There

lie between

Visual

addition,

done

the

various

great.

activity In

films

However,

of a zone

of

season

frequency"

74 ° and

geographical

auroral

disof

about

(¢m = 83°),

Z. 3.

zone.

it must

Variation

does

of

in Fig.

absence

not be

conclusion

total number

that the enhancement

must

magnetic

investigators

scaling was made by distance 80 ° on each

The

auroral

zone,

and

zone

seen

between

of the

auroral

Canada,

Z.

be

definite

the

other

allsky-camera

Resolute

station.

inner

region

statement inner

this

each

many

disturbance.

and Churchill (era= 69°)" The of auroral forms within zenith the

investigated

and

there

Z. 8 in

Geomagdisplacement for Farewell. toward earis also

(1959)

and

a

O

represents

relative

and

1956.

As

ity

located

portant night

allsky

can

be

several

seen

in

hours

difference and

3914 the

later

between

postrnidnight

A

intensity

than

the

this

College

curve

its

This

intensity

Before

during

has

the others.

auroral

hours.

over

figure,

midnight

1955

point

is due

grav-

to an

distribution the

of

im-

in premid-

auroral

forms

stand

out sharply above the low intensity of the background, but after midnight the intensity of the background is enhanced so that individual auroral forms

are

not

easily

and

DeWitt

Davis aurora

was

zone,

for

winter.

has

time)

and

on

Tromholt,

Currie and

and

1959;

and

and

1959,

find

at

of

Fig.

tion

place

from

distance

is

corrected

an for

two

the

higher

At

the

(around

geomagnetic

curves auroral

78 ° only

one

maximum

between

there

were

found

for

time

Fig.

(1964). of

maxima

at

(on

various

29

the

other

the

Fig.

2.

1),

which latitude,

expansion. in

opposite

one at

result latitude

There di-

maximum latitudes

disturbance

au-

observa-

geomagnetic

and

by in

maximum

of

only

of

IGY

resulted

of

3 in

to

for

have

geomagnetic

functions

2.8

secondary

ascaplots

unwinding

same

Fig.

possible

harmonic

dayside)

Similar of

of

the

in

been

distance

The

maxima.

ai.,

found

pronounced,

time

the

10

et

have

not of

found

Also,

occurred two

2.

Feldstein

midnight).

Malville the

function spherical

in

has

(curve

in the

Hale,

Thorson,

Loginov,

curves

geomagnetic

linear

zone,

and

(1963)

zone

Stetson

1959;

midnight.

a less

of

Vegard, 1935;

1937;

1961;

Studies

auroral

terms

Stagg,

occurrence

function

1893;

investigators

Solomatina

the

as

observed

spiral-shaped

by

showing

approximately the

rections.

sented

10

1950;

it

local

by

1933,

Chamberlain

of

fre-

2200

given

Murcray,

but

and

frequency

Fuller,

geomagnetic

1931).

Feldstein Z.

occurrence

to

hours

(Hulbert,

and

the

been

Paulsen,

a,

suggestions

morning

stations

curves

roral

many

early

to

occurrence

also

Solomatina,

close

of southern

(at about

1930;

of these

similar

been

(1960)

and

auroral

period

1886;

1959;

in which

noon.

have

1935

number

of hours

southern

auroral

Elveyetal.,1955;

Feldstein

fairly

to the

midnight

Lee,

Malville,

large

curves

the

some

Feldstein

are

A

have in

The

aurora

Davies,

1961;

maximum

There

of

1953;

1960;

with

maximum

the

1934;

variation 2.9

9.

geomagnetic

1927;

Jacka,

others.

diurnal

around

Sverdrup,

1942;

Feldstein,

1962

close

cent

in a two-months

geomagnetic

variation

Edwards,

bassen,

1960;

the per

Carlheim-GyllenskiSld,

1927;

Brooks,

night

in Fig.

around

diurnal

1882; Chree,

and

is shown

minimum

evaluated

Antarctica,

of day

result

a deep

have

at Byrd,

hour

a maximum

Reports 1912;

(1963)

observed every

Their

quency

distinguished.

has

latitudes

around in

been

pre-

have

been

measures:

e.g.

for

geomagnetic

Nikolskiy dio

aurora

radio

by

wave

On tina

for Forsyth

and

roral

zone

for this

(1961),

who

mapped

eastern

not found

by

Davis

very

on the

previous

gave

similar

surface

subsection).

The

by

extensive

of the

time

(1963

d).

over

curves

case

the

au-

of Khorosheva

similar

of Fig.

2. I0 was

studies

1962,

have

has

distribution

projections

1963)

of some

and

of the

Akasofu

aurora,

of equatorial-plane

geomagnetic

auroral

Soloma1964)

those

configurations

the

and

Akasofu,

regularity

(1960,

to the

along

re-

for

instantenous

auroral

results

instantaneous

closely

earth's

An

of oval-shaped

Akasofu

for

and

at a given

observations

simple

the

by

(196Z)

Feldstein,

proposed

parts the

b) and

made

(196Z)

were

found

and

(1959),

Feldstein

2. i0.

of momentary

and

(196Z

been other

However,

events

Chapman

has

(1957)

al.

al.

also

aurora

in Fig.

among

et

(see

for

et

(1960).

results,

curve

17 cases

2. i0.

auroral

circles

are

Burdo

Hagg

Egeland Piggot

1962)

spirals

hemisphere

to that in Fig.

and and

(1961,

shape

shape

(1955), by

observational

combined

of a similar

Support

which

(1960)

Thomas

that the precipitation

of the two

and

al.

of their

Meek

ionization

Khorosheva

shape

strong

et by

the basis

(1961)

by

sporadic-E

absorption

proposed

the

disturbances

(1957),

field lines

studies

by

(see

Morozumi

(1963)

O

at the

South

Pole

(geomagnetic

peaks

in the diurnal

for a maximum

A

theoretical latitude

siders

the

points

much

of

related as

before

than

(1963)

auroral

the main

tivity occurs

sponding

close

Feldstein processes

and

show,

therefore,

about

That

by

the

in the

that

be

they

or

noon

not

close

two

than

a

magnet-

procalcu-

effect

with

is

8 ° observed).

variations

effects

data

On

been

Detailed

the expected

are

The

day.

have

compared

con-

dayside.

in the

zones

at

one

are

are

of a common evidently of the

needed

oval

in-

reached.

to geomagnetic need

in

the

nonexistence

in the diurnal

in, or

being

(1960).

that Z ° as

observational

the existence can

on

that if the diurnal

sense

More

but

Instead

when

earth

auroral Liemohn

than

one,

zone,

obtained

wind

however,

(less

maximum

found,

is

in the night

concludes

zone

auroral

solar

by

show

occurrence.

around

the

not

a minimum.

oval

instantaneous

(1960)

a conclusion

auroral was

particles

the observed

cause.

an

S) did

at midnight,

(1959)

at all, it is only

for

latitudes

oval

Reid

yet unknown

stantaneous

78 ° , as

at lower

basis and

by Malville less

O'Brien

and

motion

78

there

for

than

are

by Rees

lations

motivation

is compressed

this theoretical posed

curve noon

at noon

drift

which

mirror

variation

at magnetic

higher osphere,

latitude

at geomagnetic

necessarily

to,

30

the

distribution

mean

equatorial

of auroral latitudes

that the plane

take

acof about

correplace

on

the

dayside,

namely

proposed

by

model

proposed That

the

arcs

Axford

the

diurnal

found

by

auroral

predominance

during

the

The

morning.

bright

auroras,

roral

zone,

fore

has

most

3.

and

often

Other

(a)

Time

Z7

day

synodic

ences

days),

for

to the

(b)

aurora

were

known

that the earth

the

in the

phenomena

auroral

the

curve

and

Elvey this

has close

quiet

some

forms

the

appearance near

type

to

have

(1958)

Pulsating

(Heppner,

is

forms

faint

for

forms

which

precedes and

midnight.

of Visual

in of

the

of aurora aurora

authere-

occurs

1954).

Auroral

with

of the

Activity

a period

sun.

of observing

close

aurora,

sun

the

by

a small

Z6

of about

and

the

but

27 days

(Meinel

recurrence

27 days,

the moon

to the solar

effect,

of the no

As

is enforced

around

apparent

synodic one.

When

definite

period

the

analysis

indication which

et al., 1954).

is

influ-

repetition lunar

remains,

tendency

which

considerably

By

of a

evidently

the

second

and

remains.

variation

subauroral two

regions

maxima

at the

frequency

to Mairan

maxima

at highest

the

annual

The

Fig. found

existence

(1733).

in geomagnetic heliographic

curve

equinoxes.

distribution

Observatory.

already

similar

being

variation

is fairly

occurrence at Yerkes

is

for

associated

brilliant

and

Romick

before

activity

rotation

has

hypothesis

incorporated

Alaska, and

generally

by

to repeat

rotations,

In the frequency

College,

hours,

hours

the lunar

Seasonal

are

different

Strong

glow

period

maximum

solar

(1954)

tend

which

one

tendency

possibilities

recurrence

third

evening

well

of auroral

is corrected

is due

the

recurrence

the

responsible

and

for

at

11).

first found

rotation

the

tendency (Z9.5

g.

Variations

Auroras the

(1935)

morning

above

differs

the diurnal

in the

evident

are

disturbances

Fig.

its maximum

is

{1961).

hydrogen

as

A fairly

described

Hines

Fuller (cf.

field

occurrence.

variation

e.g.

zone

geomagnetic

of that model

magnetic and

the

others.

lines

of a kind

for

by

of

and

or

in auroral

spiral

qualitative

been

points

maximum

Two

topology

(1960)

Johnson

that the neutral daytime

if the

It was

by

occurence

proposed

in March

the

Meinel

of spring

disturbances

latitudes

31

of auroral Z.12shows

et

and by are and

monthly al.,

fall maxima Cortie

due

(1912)

to the

September.

If this is true, the angular diameters of the solar plasma beams do usually not exceed about 5° as seen from the sun. This is certainly not so for the very largest solar events, however. The dependence of the seasonal variation on latitude is obscured by the change with latitude of the ratio of the lengths of day and night. If this change is ignored, as it usually is, then the summer minimum becomes progressively deeper with increasing latitude, while the winter minimum becomes progressively shallower, disappears and is replaced by a maximum, which is then the only one in the distribution (cf. e.g. Chree, 1911). Gartlein and Moore (1953) found that the ratio of the mean of the numbers of overhead auroras in North America occurring in June and December to that for auroras in March and September is a steadily increasing function of geomagnetic latitude. Between about 58 and 60° N the level of activity appears to be constant throughout the year. Feldstein and Shevnina (1961) investigated the seasonal variation in auroral occurrence frequency in two hours centered on local midnight-thereby eliminating the influence of the diurnal variation-for

six stations

northern

hemisphere

between and

63

for

and

five

83 ° geomagnetic

stations

between

66 ° and

netic latitude in the southern one. They found the tion as described above at and close to the auroral perceptible roral

seasonal

variation

in auroral

latitude

in the

90 ° geomag-

same seasonal variazones, but no

frequency

on

the

central

au-

caps.

(c)

Sunspot

Fig. tween

cycle

Z. 13,

the number

between

1761

and

the

lar

correlation

occurred,

and

1877 seem

after

delay

of the maximum

solar

activity

but

the delay

4.

Orientation

Hitherto

and

1897 during

sunspot

and

only

various

per

sunspot

auroral 1951.

those

shows

The

The

(1937)

frequency 3 solar

too,

of aurora cycles

a simi-

at Yerkes

auroral sunspot

is good

found

made

maximum year

be-

in Norway

correlation

observations

5 eleven

the

correlation

observed

et al. , (1954)

Egedal

during

the

year,

number.

Meinel

occurrence

activity

cycles found

some

in relation

from

Z

a time

1897

to

to the 1929,

1 year.

of Auroral

parameters

the

(1902),

aurora

maximum.

in Denmark was

with

analyzing

between however, the

Tromholt

to coincide.

when

years

tistical

after of days

maxima

Observatory

variation

Arcs

characteristics describing

the

or

auroral

probability

3Z

"activity," of occurrence

i.e.

of sta-

of aurora,

have

been

this

section

ured

from {a}

described. the

Average

auroral

tend

majority quiet

the

oriented

of the and

often periods

A fairly extensive Hultqvist, 196Z of circles

geomagnetic

tional

the

material,

alignment projection jections served

made for

azimuths

tigated the geomagnetic

be

detail.

In

readily

meas-

and

discussed directions

of such included

values

fact

from

on

circle

the

of all the

ob-

of the nightnot considered.

earth's

Z. 14 pro-

surface

along

the

observa-

Fig.

concerning

2. 14 that,

to the direction that the agreement geomagnetic cases, greater

eastern deviate

that

1958).

of the circle projections where this is under 90 ° .

in

general,

the

of the relevant with the circle latitude than

circles. The ob90 ° in those quadrants

exceeds 90 ° , and Thus, it has been

and western in opposite

circle pro-

coasts directions

less than verified

of Greenland the from 90 ° , as

projections.

Feldstein

(1960)

of arcs circles

and

Evans

at two places differ greatly

auroral zone the prefered

and Halley Bay near direction of alignment

netic latitude projections,

circles, than with

and the

of accurate

average The

reservations

evident

A

data is contained in Fig. are a number of computed

plane

(Hultqvist,

field.

by Fritz (1881). to the geomagnetic number

estimated.

of auquiet

approximately

geomagnetic

investigations

equatorial

lines

than with the is in most

alignment latitude

direction, of the

were the

were

collection b). Also

of the

orientation showed that

only during a certain period different investigations-was

experimentally that on the observed average azimuths

Starkov

can

made a large Scandinavia.

pre-IGY

arcs conforms closely, and

is better arc azimuth

the

into

discussed.

in a preferred

above-mentioned it is

of the quite

where the azimuth 90 ° in quadrants

do

which be

component

bands

in the field

Despite

more

data on the average studies of aurora

investigations (19Z0) referred

arcs

servations were and in different

jections

much early

and the Norwegian school determinations in northern

In the

(after

arcs, will

horizontal

of these early and Krogness

observed

somewhat

of auroral

to be

to the

meridian direction

go

orientation

perpendicular number Vegard

will

recordings,

exist fairly Even the very

arcs

we

orientation

photographic

There arcs.

roral

Now

and where {Dixon

the southern is far more

therefore isoclines.

with

33

Thomas

the

inves-

the isoclines and near the northern

one). They consistent higher

{1959)

found with

approximation

the

that geomagcircle

The are

available

relatively

contained

exiguous.

in Fig.

directions, arrows

as

As

seen

from

directions good

with for

better

all

than

those

Because auroral

and

of the circle

riod

arcs,

(e.g.

point

the

arc

accord

material

of Fig.

Table the

Fig.

with

(1961),

for

is after

(b)

Diurnal

for

stations

dii-ections

if values The

shows

of quiet

8-13

results

for the

values

auroral

from

arcs

northern for

after

Feldstein

variation

in

it was

the

evident

orientation

from

auroral

until the

allsky-camera December

arcs

were

in

the

direction

to end

estimated.

of an

pe-

a com-

of the selected

of Fig.

Z. 14.

at local

midnight

geomagnetic

stations

i-7

(1960),

and

arc

probably

near

and

in

meridian

are

taken

of 1962,

Only

arcs

after

Davis

that for

and

34

not

even

exceed

at

now

from

4° .

of 559 horizon

of

only

(era= 65.3 ° N)

directions

reaching

zones

that the directions little attention was

at Kiruna the

auroral

of Bravais

distant ones, covering in the analysis. The does

the

observations

ninteen-thirties,

recordings 1958

izon or, in the case of the most of view of about 100 ° were used ured

arcs

(1945).

paid to this phenomenon few studies exist.

From

of such

of

of them in or near 2 and Fig. 2. 16. A concordance

Bossekopin northern Norway as early as 1838-40 the arcs and bands show a diurnal variation, very

the period

certainly

a short

is better

azimuths are

fairly

is

of the

for

that the

the unselected

observed

Harang

Although

compared.

(measured

The

the

expected

projections

azimuths

hemisphere

those

Troms_

circle

is

in the orientation

at twelve stations, most are presented in Table

Z. 16 than

the east).

circles

agreement

variation

between

2. 14 clearly

the

Z contains

northern

towards

are

observed

circles.

is to be

of the night

of the

results.

between

the

during

in direction of the

plane

and

of a diurnal

increased

with

directions

9),

of

Two

of observations

agreement

latitude

existence

results

equator

(No.

is

elevation.

differences

the

data

of observations

the uncertainty

15,

hemisphere

subsequent

results

of highest

The

projected Byrd

parison for local midnight the northern auroral zone, comparison

Z.

southern

and

the

1958.

Fig.

projections

1 hr)

represent

and

geomagnetic

of the

the

auroral

except

the

of IOY

demonstrate

of

places for

indicate

station

will

be

arrows

1957

years

the

collection

single

two

for

A

to the

for the

results

The

years

of the two

arrows

2. 15.

sighted

for any

each

observational

in

quiet to hor-

an azimuth error in the

angle meas-

Table

Station

No.

Geomagn. Coord. °N

Z

Observed

Approx. measure of deviation

azimuth °E

(degr.)

Azimuth of circle projection ("theor. azimuth")

Diff. obs. azimuth and "theor. azimuth"

i

1

Baker

Lake

73.8

314.8

Diff. max

94

_60

-min

93

O

Z

Churchill

68.8

322.5

99

Diff. max -rain o 60

95

4

3

Barrow

68.6

Z41.Z

92

Diff. max -min o _60

84

8

4

Fort

66.6

256.8

9O

Diff. max -rain o _80

87

3

5

College

64.6

256.5

86

Diff.

max-rain _60 °

87

-i

6

Farewell

61.4

253.2

83

Diff.

maxmin _60 °

86

-3

7

Choteau

55.5

306.0

88

Diff.

max-min _70 °

95

-7

8

Schmidt

62.6

226.6

8O

Diff.

max-rain _30 °

8O

0

9

Dixon

63

162

98

Stand.

deviat.

98

0

°

I00

3

±15 °

ll3

-2

Yukon



I_.Arcs w,th ray-struclt_r¢

.-_ orape___m

---

,C"2._.

L

,o t 6O

I, 40

I

I 20

i

I

I 20

I

I zg)

i

I 60

J

i 80

I

J tO0

i

Number

Fig.

Z. 24-

(After

Vegard limits

and Krogness, 1920) Distribution for different auroral forms.

of lower

t20

.8 m

A

m

O

m_ °r-¢

00 m

f

!

O

4-( (27", O c_l 00

.c_ :o .,-I

,._ o k

O _.,q.

D

i,m

j

m

_

k

o-g

O ,.O k

_

u_

LI

t%l

m

._

° ° _mm

I

° _

°

°

c0 O

o

=

=

¢) O

g_o

o

i.i u

N o

° _

o

Ld

g/

U 0 _1

N ©

I

/

_

°e,l

_

_._

°_,-4

/

N

_

or'l

/

m

/

,._

0

o

/

c_

__

v

I t _-

_ _ _

0

_

I

I

I

I

I

I

I

I

I

I

m

0

o

0 3011111¥7

3113NOVM030

"'_

•

"_

._

o,-_ _1

_

0

_m

80

70

B

9

60 I

5O

4O

"

I " I " I !

•

| !

-

30

•

!

J

'.

20'

Draperies

th ray.-struc

10

-----"

Fig.

Light

Z.Z6-(After

intensity

Harang,

tribution of light intensity ferent auroral forms.

1951) along

Disdif-

14 -

I0

-

_

INCIDENCE .

.j

MAX

KCO

>5

-

m

'_'_,_.,. MAX. I r_-_

I i

0-

I

,,,

B

I-_ _ 60 z,.,u UU e'O

I

I

I

PERCENT

n

_

OCCURRENCE 19-05

HRS

--STRON_

O

I

I

I

I

Cf

,.-I,

"_.

WEAK

j

90 I o

I

_

_

KCO ':5 I

I

I

I

_

K

i

_

I

INCIDENCE

STRONG

Ilg

...

9_

_'-_TRONG

70

68

Fig.

66 GEOMAGNETIC

2.28-(After

measures

of

Davis,

auroral

itude for weak

and

inAlaskainthe of

total

64 LATITUDE

62

1962b)

activity

strong

for

Several

versus

displays

season1957-58.

incidence

25

60 °

lat-

observed (A) Curves

displays

during

which the maximum did not exceed 5

K-index for College (dashed line) and for 25

displays

it exceeded

(B)

for which

Average

percentage

of overhead

auroras

19,05 h ) during (C)

Total

strong curves moving strong

and

(C)

forms and

30

and

observed weak

weak

displays.

interval displays.

during

displays

Total

occurrence

time

of forms

24 weak

B.

(local

24 strong

incidence

5 (solidline).

hourly

used

south

and

throughout

the

24

to draw north 31

0

Q; (D

_

.,-4

o o

o_ 0

0

o

o

°r,,I _-_

_ _j

_

0

0

_

om

_o_ "a_-

.a

_o_

_o

_'_ _

-,_

o,___

o _,'_

u

0

3. In

Correlation

this

and

solar

i.

Solar

section and

the

with page and

number

planetary

of

the

3Z), solar

Since

magnetic reached

recurrence

than

for

magnetic

aurora Uppsala,

of

aurora

be

in

occurrence mentioned

storms seems

in

the correlation have been made.

solar

(cf. below),

fre-

events

and

most

between A

geomag-

in Chapter aurora and

of

of the

are

also

valid

to be

less

pronounced

relevant

for

aurora. for

aurora

1961).

discovered

in

of

and the

has

been

in

subauroral

known in

by

only may

times

Celsius

long

day

the

been to

Hiorter

when

in

in

by

Barrels

investigators

invariably

the

seen

occurrence

made

aurora

almost

latitudes

be

when and

between

zone

aurora

the

1940).

has

for

the

auroral

latitudes

little

1741

Barrels,

activity

storm

aurora

at

correlation

magnetic

It

very

in

Chapman

a magnetic of

occur

the

storm the

leads

to

following is

a

auroral

night.

strong

one

zone

(see

Z).

visual

the

central

aurora

planetary latitudes

is

K

ireldstein Murchison a weak south

polar

75

and

80 °

the is

(196Zb)

found

Bay

{geomagnetic

magnetic

that

taken

between

{K

= Z-3).

account

57

of

observed

75 °N) the

as

as

with

occurrence

in

the

frequently

When

auroras occurrence

the

geomagnetic and

a transitional

most auroral

80 ° ) the

well

between

auroral and

are

latitude

above

local

region

complicated auroras

into

the

In the

relationship more

latitude

with

1963).

disturbance also

{geomagnetic

correlated

{Davis,

activity

were

caps

negatively

indices

geomagnetic

the

the

been

of to

not

disturbances

planetary

of

cases

Over

is

have

{Chamberlain,

was

{1958).

occurrence

Section

is good

investigation

true

of

between

magnetic

{cf.

the

start

is

which

relations

magnetic

observed

and

which

reviewed.

variation

investigations seem

tendency

Sweden

Chapman

This

briefly

aurora

Disturbances

A detailed

the

for

worldwide can

in

the

cycle,

disturbances

Geomagnetic

the

be

visual

in the literature and are reviewed correlation between occurrence

activity

Z7-day

That

solar

of

exist the

The

and

Phenomena between

will

of

detailed disturbances

studies

conclusions

that

Geophysical

phenomena

investigations

aurora

netic disturbances of this book.

Z.

and

statisticalrelations

geophysical

Z {see aurora

large

observed

for

of

Section visual

Solar

Disturbances

Except quency

with

nature.

zenith

at when

there

appearing frequency

to

-

increased found

with

positive

disturbance

K-index

is not

visual

only

as

of the associated

been

studied

by

(1953,

ultaneous

(1954b)

be

in the following

auroral

activity

represented

disturbances

The

by

each

bay

patterns

horizontal

distinct

change

from

College slowly

observed the

pattern) the

A nosity

period

have

Zabor-

(1959)

and

has

close and

quiet

and

Close

following

during

pattern).

geomagnetic

between

also

rapid

micropulsations

Campbell(1960 (see

A

bay

north

as

luminosity

bay up

sets

(first

of Heppner

during

the

of cases horizontal

arc

or

than

is generally

pattern

the

homogeneous

The

breaks

majority

in which

far

a

time

a negative

and

place

being

frequent

glow).

when

from undergoes

appear-

there

is

magnetic

is frequently

this period.

correlation

(1963)

and

takes

bay

disturbance

at this

magnetic

In the

the negative

that coinactivity.

the

aurora

In the first

component

is positive.

when

southward

aurora.

and

is more

to the moment

(second

individually

of auroral

the

sim-

all, nights

that magnetic

is generally

(arcs

moves

apply

it disappears

positive

and

field changes

aurora

forms A

active,

pulsating

the

(geomagn.

perhaps

disturbances

first pattern

night

and

happens

second

The

at College

which

geomagnetic

in the

equatorwards.

component

again

Nebel(1959), Berger

and

to what

of the

of the horizontal

disturbance formed

develop-

1955),

of recognizing

In the first pattern

of the

becomes

of diffuse

a short

development the

disturbance

patterns,

sequence

and

disappears

recovery

ance

of

relations

et al.

of,

is a distinct

in respect

in this period. aurora or

of two

far northward.

part

magnetic

majority

bay

negative.

In the early

The

a large

of individual

there

in form

recedes very the second.

advances

up

component

to being

in,

the and

These

observations

is a consequence

differ

positive

seen

made

his

way.

on

means

This

are

with

two

in the

between

latitudes,

Bless

Pole).

occurrence

(1954a,b,

(1958),

(1963)

magnetic

South

general

exists zone

Heppner

Fan

summarizes

in combination.

cident

the

disturbance.

1954b),

(1957),

and

(at the

between

in auroral

Morozumi

occurrence

latitude

relationship

seen

of it.

(1963d).

lat. 64.5°N)

or

Meek

values

auroral

geomagnetic

Fediakina

Heppner

may

between

detailed

ment

Akasofu

high

a correlation

aurora,

shchikovand

to

at 78 ° geomagnetic

but a fairly

of the

up

correlation

even

There aurora,

the

a,b,c), Chapter

variations has Campbell

).

58

in the auroral

been

found

and

Rees

by

lumi-

Campbell

(1961)

and

and

3. Earth Currents The

occurrence

wires

was

height

measurements

used

a warning

by

aurora

earth of

StSrmer

of

Wescott,

accumulation

auroras,

with occur

to

the

the

two

corresponding

phenomena

an

for

influx

telegraph

paralactic

As

years

the

is,

cases.

at

earth's

good

reported

of negative

precision and the

The

however, has

as

electric

with adequate electrical field

(1961) the

long

many

night.

in individual

charges

to

next

not known induced

the

in for

success

the

Freier

negative

voltages program

good in

aurora

1959). of

induced

extensive

is generally details of

currents

and

of

his

aurora

would

occurrence

Hessler

day

in

of the ground to relate the

resulting lation

the

on

that

conductivity it is difficult

the

during

corre-

(cf.

e.g.

evidence

surface

for

during

charges

into

the

upper

atmosphere.

4.

Radio

Aurora

Reflections

of

frequencies radio

of aurora

(1938,

were

America, and

The zone

see

for

an

The

seasonal

The

long

Z years

Radio aurora. very

narrow the

same

the

height height

aurora

and

the

1930's particularly

-

Stoffregen

by

is

amateur during

a number

of

Germany,

of radio

critical

ionization

and by

(1962),

activity,

power

range

well

has

with as

far

as as

zone

Russia,

aurora

the

researchers

with

Hultqvist

and

observed

in the

as

same

auroral

New detailed

Egeland

has

value

59

at the

visual

echoes

can

3. i).

equinoxes. about

aurora.

regions

as be

optical recorded

zones.

to take

between

border

auroral (Fig.

its maximum

with

general type

found

maximum

maxima

the auroral

been

mean

has

is the case

from

the lower

a night

variation

in the

radars

process

interval

aurora

as

frequency

in latitudes

reflection

in

Sweden,

of radio

is observed

high

even

Harang

auroral

war

a review

in the auroral

solar

aurora

by

via

studied

Egeland

maximum

occurrence

With

often

The

variation

variation

after

For

the with

(1964).

afternoon

term

been

Norway,

instance

Leadabrand

1938

earlier

has

Britain, Antarctic.

diurnal

has

in

world

above

associated

propagation

second

aurora

the

references, and

the

well

ionization

discovered

radio

Z@aland

frequencies

investigated wave

After

in North

(1964)

first

however,

years

of from

radio

operators. ten

waves

ionosphere

That

was,

radio last

-

1940).

possible

radio

the

90

of visual

place and

in a fairly ll0

kin,

aurora,

by

i.e.

in

a large

number

of

investigators.

quite

wellwith

Fig.

3.2

radio

aurora.

Also

those

shows

of

visible

can

The

be

seen,

does

not give

The are

echoes

mentioned

found

is

sensitive: to

any

to

the

the

magnetic

stood

if

the

field

strongly reflection

a critical

ities.

Recently

sound

waves

echoes the

same

et

small

al.

is

,

5.

1964)

it

zero

the

But

the

1963).

fine of

overhead

auroral

echoes

is

aspect

a direction

perpendicular

This

can

be

scattering

lines

of

the

as

small

well

as

if

irregular-

irregularities of

reflecting

under-

from

force,

structure

may the

centers

by

ion

received are

be

of

active

be

at

fairly

well

Anderson,

seems

that

well to

be

(see fairly

to

the

most -

refractive part

of

the

clear.

large

of

scale and

VHF

See

1962;

Anderson

auroral

luminosity 3.4,

exceptionai

after in

x-rays

the

is and and

activity. of

in

x-ray

quite 1960).

flux and

zone

the

general

Enemark,

Anderson auroral

has

magnetic

precipitation

bremsstrahlung,

60

the

reflection

from

occurrence

aurora

Fig.

from

Altitudes of

generate

far

Mc/s

details.

correlated

1960,

happen

extremely

Balloon

between

which

is

that

2850

scattering

lowermost is

more

probability

correlation

(cf.

This

the

the

to

critical

large

produced for

weak

distribution so

in

are

up

whereas

importance

at

that

density density

papers

frequencies

probable

frequencies,

electron

zone

however, other

most

for

electron

X-rays

to

there

each

which

weak

the

observed

an

electrons,

does,

the

review

detailed

energetic

been

higher

may

auroral

found the

poor

of

that

The

irregularities

Bremsstrahlung

been

or geomagsouthern

magnetic-field-aligned

suggested

seems

in at

mentioned

In

elevation

aurora

point.

one

along

number

has

from

How

above

not perfect

at low

mechanism

reflection

1963).

aurora

reflection

band.

in from

larger

been

a large

process

index

regions reflection

is

from

irregularities

i.e.

the

elongated

has

that

radio

important

It

it

but

p.44).

and

time.

As (Groth

at

(Buneman,

shows

the

the

mechanism

it

Z (see

of visual

only

strong

predominantly

lines

irregularities is

that

occur

reflection

Section

around geographic and south in the

extremely

of

fact

reflections

good

correlate

at all.

limitations

due

in

is a significant

somewhere hemisphere, Even

aurora

recording

is, however,

3.3).

radio

described

there

correlation

(cf. Fig.

of

of simultaneous

angles in a sector centered netic north, in the northern hemisphere

motions

aurora,

an example As

correlation.

the

foliow

DeWitt, latitudes.

In subauroral latitudes strong x-ray events occur almost only during strong magnetic storms, and the correlation between the occurrence of visual aurora and bremsstrahlung at balloon heights is quite good (see the review by Winckler, 1962, for instance). The balloon responsible tute the aurora

6.

the

The detail

in

Auroral

spectrum

Rates

the magnitude short

This

the

SIDs type

is no

has

phase

and

Even

is

not

consti-

the visible subauroral

in

discussed

in

•

•

no

if

there, and

visible

with

any

some

Ansari when

auroral

shows

with

type,

reported form

regard

aurora

(cf. Chapter observed

that Ansari than

occurring

one

type

of

spectrum in the pre-

the visual

aurora

(see

to the luminous

( 4.

satellite

for

daily value

electrons

Brown,

the variable

combinations electrons

x-rays

primary

producing

explains

the the

energy

the

the

summer

should

days to

in

activity

month, For

when

the

db during

each

the

This

1964,

fluxes

in

the quiet is identical

to the 1963,

in

1 db

bremsstrahlung

compared

from

magnetic

(1963).

profile

flux

and0.09 of

days

equinoxes.

For which

db, absorption

Basler

about

electron

ranges

quiet

density

computed

4 as spectrum

db

limit

2 sec

given

the

by

the

spectrum

is

the

equivalent

found by is curve

68

as in

McDiarmid No. 1.

and

absorp-

spectrum

coming

in

1.9

db

and

(1964a).

to

three

well the

equilibrium 3.8

db

the

is

Hultqvist

spectra are

-1

Z

mentioned

energy

kev)

due

Curves

is 0.Z7

absorption

After

for

the curve

represent

differential

profiles

Mc/s

elec-

under

at night.

day

produced

e-_/s

of the

in the

daytime db.

The

Z7.6

produced key)-1

absorption

= 5.109

to 0.89

(cm

electrons.

No.

N(E)

3, finally,

by

density

at

of the

absorption

Total is

A,

fluxes limit

et al. (1959).

allsky-camera

total absorption

and

electrons

absorption,

ster

from

to the bremsstrahlung

produced

electron

Z gives

The

day

Total

one

precipitated

spectrum

kev) -I.

lines.

nighttime

sec

curves

to the geomagnetic

Leadabrand

altitude.

distribution

in the

-E/41

3.6-Equilibrium of

to the various

obtained

at balloon

due

0.061

tion distribution

along

with

of range and The points repre-

regard

After

luminosity

energy

spectrum.

in the night N(E)

with

point.

height

ster

amounts the

attached

angle

flux

differential (cm

electron

compared at College,

a function Z6, 1957.

numbers

reflection

x-ray

aurora obtained

(1963).

1 show

trons

Fig.

of

of auroral

DeWitt

aurora

(1954).

observations.

at the

for radio (geomagnetic

(1962a).

radar

Bowles

sent

pictures

Fig.

Egeland

3.3-Mass plot of 398/Mc/s echoes as azimuth, College, Alaska, March

field lines Fig.

After

photographs 106 Mc/s

Alaska.

Fig.

of the occurrence frequency observed at Kiruna, Sweden

65.3°).

3.2-Allsky-camera simultaneous

Captions

energy as

the

spectra total

figure.

Curve

electron • 104

spectrum et After

e -E/s° for

density electrons the

al. (1963) Hultqvist

average a lower (1964b).

(cm

2

Fig.

3.7-Diurnal noise PCA's

variation

of the for

the

occurred

are

excluded.

for the following months: 1959, March 1960, October tember 1961, and October alone Fig.

3.8-A

average

absorption

and

curve

simultaneous

3 for

intensity

equinoxes

at

of 27.6

Kiruna.

Curve

1 represents

April 1959, September 1960, March 1961, 1961. Curve 2 is for

September

observation

1959. of VLF

auroral luminosity and precipitated on March 3, 1963,0720-0725 UT. (1963).

69

Mc/s

Months

After

cosmic in which

the

average

1959, October April 1961, SepSeptember 1961 Hultqvist

electromagnetic electrons on After Gurnett

(1963a). emission,

board Injun and O'Brien

3

Fig. 3.2-Allsky-camera photographs of visible a u r o r a c o m p a r e d with simultaneous 106 M c / s r a d a r e c h o e s obtained a t College, Alaska. After Bowles (1954).

i'

0

0

0

0

0

0

0

0

0 0

104 . i .

I

-

MARCH

'

I

I

5, 1962 rr

_)

I

iO_--

RAYS

>25

keY

U

_

3o

8 z 2.0 -_

_> 1ol I "" .... 1200

Fig.

_,,

1230

3.4-Comparison

camera and

t

pictures

DeWitt

(1963).

1300 1317 UNIVERSAL TIME

of with

1.o""

auroral

x-ray

flux

luminosity at balloon

1400

obtained altitude.

1430

from After

allskyAnderson

140

140.

NIGHT

DAY 130

130

120

120

I10

I10

E I00

I00

90

90

80

80

70

70

60

60

50

50

W

b-b--

40

40 0

2

4

6

8

I0

12

0

2

4

6

8

I0

12

Fig. 3.5-Curves 1 show the height distribution of the absorption produced by the differential energy spectrum N(E) = 5.109 e-E/s electrons (cm 2 sec ster key) -I The total absorption under to 1.04 db in the day and to 0.89 db at night. Curves tion due to the bremsstrahlung

of the mentioned

the curve amounts 2 give the absorpelectron

spectrum.

Total absorption in the day is 0.27 db and in the night 0.061 db. Curves 3, finally,represent the absorption distribution produced by the differential energy coming

spectrum

N(E)

= 7.104

in along the field lines. Total

the nighttime

one is 0.52 db.

After

e-E/4z electrons daytime

Hultqvist

(cm 2 sec kev) -I

absorption (1964a).

is 1.9 db and

140 I 30

I

I

I

m

120 I10 I00 Km

90

/

/

/ 80 70 60 50 I

40 I02

I

tO3

I

iO4 electrons/cm

tOs

I01

3

Fig. 3.6-Equilibrium electron density profiles due to three energy spectra of precipitated electrons. The spectra as well as the total absorption,

A,

at 27.6 Mc/s

are given in the figure.

Curve

No. 2 gives

an upper duced by

limit for the equilibrium electron density distribution prothe spectrum 3.8 • l04 e -E/3° electrons (cm 2 sec ster kev) -I

which is the equivalent spectrum for the average fluxes when Kp > 4 as found by McDiarmid et ai.(1963) a lower limit for this spectrum is curve

No.

1. After Hultqvist

(1964b).

Absorption 2 db

in the first

•

i

minute of each hour

|

!

i

i

!

A

#

/

,i

a.

/ # i

/

i

/ /I

!_ A

/

l

_,\_) _

_.._

;v l

•

3

6

9

Peak absorption

12

for each

.j

15

18

21

hour

I^"

2

b,

._t j

db

/,

\

,

fj/

•

,

24 MET

\

',

"

,'/

_,

-_.

v _\

Q A'

#

d 0

i

i

u

u

!

i

I

3

6

9

12

15

18

21

2,4 MET

Fig. 3.7-Diurnalvariation of the average intensity of Z7.6 Mc/s cosmic noise absorption Months

for in

the

which

cluded.

Curve

for

following

the

September 1960,

equinoxes PCA's

I represents

October

196 i, September Z

is

curve

3

for

for

1959,

March

1959,

1961,

1961 1959.

ex-

March

196 I, and October September

September

qvist (I 963a).

are

average

April

October 1960,

Kiruna.

the

months:

1959,

Curve

at

occurred

alone After

April

196 I. and Hult-

L (EARTH I

"

--

;_

[ _ [ m lilo_ t ,., I_ J--

7,

6v

'

9l

8,

RADII)

tO •

_"

14 16t620 , _ , J

E---WIDE BAND MAGNET-iC -_E(_O ..... -] IITRENGTH (7 KC/5 NOIIEBkNI)_WJD_TJ_ .... --VI_F RECEIVER NOISE:LEVEL

|-',0"1-

I ............

,o,_ .......... :" ' '" .......... "!

•"

t

•r.. i07_--

l

§

I

k

_,ef:/

"'.

r--'_

I SPECTRAL DENSlTYI

........:.

L_ AT__2.T__K_S__J

... I........."' ...,......-.............-_.._. ....... o..*.,..,.°

•

z _ 10.-7[-_ F-

o....

_

| . .. / :. • ."--:..'.'.:. ".....

......

L AT 5.5_KC/S._J .. ,.-.. !

"-. ,..,":

-

¢_

_[

/

I

......... ....

L

AT e.e_..K_c_____J

,..........."....--...:............:. ....

• ,-" I

I::-

£,_ ,_...-....-........ ..

'

8A H_ -

>n,,

_.p

,
_40

than

published

degrees

degrees.

results

the percentage

from has

70

presented

The

auroras

of precipitated

of interest

latitudes.

of

on the been

(1963).

a few

range

kev

and

auroral

data

above larger

of the invariant

seen

40

60

electrons

with

range

be

>

Similar

their

al.

at the most

subauroral

the

ten.

for

et

the

can E

A between

lower of

for

data

recently

3 observations

in the latitude

degrees.

for

have

Injun

(i/L) I/2 and

latitude

that

of magnitude

statistical

electrons

1964)

orders

shown

4.1).

precipitated

diagram

have

1964).

close as

to the

observed 1964).

4.

Electron precipitation occurs simultaneously in magnetically conjugate areas at least sometimes, according to balloon observations of x-rays (Brown et al., 1963). This is in accordance with observations of aurora (cf. e.g. DeWitt, 1962). A I00 fold change in the flux over two km has often been observed by Injun 3, which is in agreement with results of rocket measurements in aurora by Davis et al. (1960). They found the electron flux being concentrated in the visible auroral forms, whereas protons were found over a much larger volume than that occupied by the aurora. The with

E

statistical >40

latitude

kev

has

profile

been

found

maximum at a few degrees rence of visual aurora as the

visual

emission

precipitation

of

electrons the

of

higher

with

has

the

E < 40

lower

O'Brien

and

never

are

Taylor,

observed

to

of

was

found

It can

be

up

and

near

than

in the 4.Z

about

The

the

radii).

latitudinal over This

L

have

latitudes 40

kev,

to

higher

of

the

its

than

the

indicating latitudes

aurora

than

coincides

(OtBrien,

4.4

also

give and

auroral

a good

At

extent

% l earth

is illustrated

or

in Fig.

very 4.5.

74

electrons

(cm

emission

in the rate

emission L

zone

1964;

ster) -I

auroral

zone

the enormous

are

values

figure.

This

can

be

very

(over

L

3

2 sec

at all latitudes,

extensive

Injun was

is, however,

about

= 6 there in the there.

by

= 6 there

emission zone.

of the precipitation

radius)

at L

impression

photon

zone.

auroral

that

80

photon

6.106 electrons (cm 2 sec ster) "I shown 105 times the minimum value observed

(e.g.,

to

of occurSometimes

precipitation

in Fig.

continuous

of precipitation

especially

higher than

limit

all the time seen

flux lower

corresponding

variability

to

appreciable

electrons

(1964)

the frequency satellite.

greater latitude

dumped

1964).

any

4.Z

than same

extend

is evident from Fig. 4.4. The minimum below visual threshold even in the auroral

Figs.

of Taylor

precipitated

lower

limit

and

energy

being The

latitude

1964).

The

key

intensity

latitude on the

found

with

ones.

Precipitation (O'Brien,

been

the

O'Brien

lower observed

electrons

energy

of

by

but

of about is some

restricted > Z0

earth

(b) Time Characteristics

of Precipitation

It is not possible to differ between time and space variations in satellite measurements. Balloon observations show, however, that time variations as rapid as of periods of a tenth of a second can occur in the electron flux (Winckler et al., 1962). No systematic over

periods

the Injuns

as

as

flux

tc_ be

earth

sary

for

(c)

O'Brien

(1962a, angle

flux

made

also

tendency

of precipitation

electrons

..;_ of the

however,

variation

neces-

curves.

earth's

important.

by

has

becomes

has

electrons

of E

in the

been

> 40

higher

by

key

of strong

et al.

(1962)

in which

the

than

the

of intense

in regions

found

mentioned

the

found

regions

Krasovskii been

over

been

is

equal

the

at an direc-

correspond-

observations

were

atmosphere.

seems

to indicate

along This,

of electrons of the

that

distribution

have

The

the precipitation

is increased

rule

isotropy

electrons

atmosphere.

the role

is not

polarof the

variability

electrons

also

angle

cases

to isotropy

tions

that

oriented

seems,

diurnal

daytime

kev--as

._,o_

where

that for

observed

No

it is directed

from

which a general

electrons.

to the

away

suggest

than

distribution

of data

aurora,

pitch

been

i0 kev.

close

the

the

approaches

isotropic

trapped

electrons--if

of an

from

for trapped

0.08--Z4

enormous

of precipitated

namely

of precipitated

fairly

The the

has

for

the

amount

(1964) case

nighttime

_h_,_ _,,__

significant

electrons,

b, 1964)

of about

ing value

flux

i illustrates

An

precipitation

the

range

lifetime

With

that over

distribution

precipitation.

a higher

th_ _ay_

1964).

O'Brien

with

the energy

precipitation

Distribution

of trapped

Figure

found

a large

directional

aurora.

tional

on

by

energy

5 days

also

statistically

i shows

to the flux

the

They

et al.,

Angle

the

energy

in the

phenomenon

Figure intense

pitch

observed

deducting

Pitch

be found

of electron

in contrast

of electrons

harder

(Johnson

precipitation

could

et al. (1964)

satellite.

elect_nnq

intensity

as a day

of protons--during

orbiting

in the

3 measurements,

Sharp

precipitation well

long

! and

electrons.

variation

that the

acceleration

the field lines--takes as well

from

ionosphere O'Brien

above

mentioned

i000

km

in the production (1964)

75

as the

found

place

of

far

observa-

in auroras, of the

a flux upwards

energetic along

the field lines, which was some 10%of the precipitated electron flux. He interpreted these observations as backscattering of electrons from the atmosphere.

(d) Kp - Dependence of Precipitation The Kp dependence of the precipitation of electrons of energy above 40 key is illustrated in Fig. 4.3. The average intensity was ten times higher near the auroral zone when Kpwas above 4 than when it was below 4 • The data material for the higher Kp range in Fig. 4.3 does not

contain

may

be

data

O'Brien 40

kev

A

close

for

any

(1964)

increased

strong

found on

magnetic

the

0.08-Z4

together

with

observed

storm,

range

Injun

3

in

the dependence

1963).

close

to the

by

so

still higher

of precipitated a factor

precipitation

energy

on

in the

(Freeman, larger

average

between

kev

obtained

that the flux

the

correlation

results,

as

from

values

expected.

by a

intensity

Sharp

low

are

of the

omnidirectional

plane

far

As

seen,

can

be

(at one

from

the

end

preferentially

parallel

was

in

Fig.

above

by

Kp dependence

of Kp.

observed

O'Brien's

shown

earth

above

step

also

flux

the

4.6

40

key

Explorer

is very

of the field line) than

torial plane (at the middle of the field line). increases are due to a common acceleration it acts

every

et al. (1964).

orbit,

equatorial

earth

electrons

of 5 for

IZ

much

in the

equa-

If one assumes that both mechanism it follows that

to the geomagnetic

field lines

(O'Brien,

1964).

The Fig.

change

4.6b,

of E _> 2 Mev

The

of omnidirectional

is opposite (Arnoldy

dependence

activity

has

used

data for

trapped

of the terms

was

of energy For

studied

has

above

this boundary,

40

kev

Maehlum but

(1963)

boundary could

measured

their

found of the

be

observed

in L,

they

76

shown

in

electrons

of precipitation O'Brien

O'Brien

close

on

(1963).

(1964)

to the

results

of precipitated

Kp,

for

et al., 196Z).

and

since

with

observed

boundary

electrons,

O'Brien sharp

40 kev

been

Hoffman

its maximum

extension

and a very

by

electrons,

of trapped

of possible Maehlum

there

been

above

mostly

et al., 1960;

precipitation

region

flux

has

of the poleward

netic

that the

to what

has

be

They shown

poleward

may

mag-

boundary

interpreted

in

electrons.

that during region

at about used

magnetic

where

the

storms

trapped

I000 symbol

km

electrons altitude.

L n.

It can

be

seen 4.7. value

as

a function of the Kp index during one geomagnetic Kp reached its maximum value of 9, L had of 4. Maehlum and O'Brien (1963) also found that

edge during

of

storm in Fig. its minimum the poleward

When

strong radio the storm.

wave

absorption

followed

the

L n quite

closely

The effect of Kp on L n is similar to the equatorward movement of the region of visual aurora during strong magnetic storms, which has been studied in the last few years in detail for some storms by Akasofu (1962, 1963a,b) Akasofu and Chapman (1962) and Davis and Kimball (1962).

(e)

The

Spectrum

of Precipitated

Up to now of the precipitated proposed spectra

only

rough electrons have been

Electrons

measurements of have been reported. obtained from two

the

energy In most instruments

spectrum cases the with differ-

ent energy characteristics. They thus are to be considered as rough equivalent spectra for measurements made in a defined way. In addition, it has been found that the equivalent spectrum is highly variable both in space and time (cf. O'Brien et al., 1962). Nonetheless the available spectral

data

are

the field, and they conclusions about Section 3). Most two

spectra

categories

hand,

the

steep

interest

even make ionospheric

that

have

if they e-folding

written in the key (McIlwain, very

of great

are

spectrum,

been b,

reported

even

has 1963; steeper

Krassovskii

cipitated 14 key.

electrons

The Geiger about much

majority

et al.

(196Z)

with

a most

of the

existing

has common

of knowledge

in

interesting electrons

be

(see

divided

form.

On

of precipitated

in one

electrons,

been found often to be in the range2-8 Sharp et al. 1964 a,b,c.) This is ones

have

been

observed.

Mc-

in a strong aurora as with an energy of about

observed

steep

equivalent

measurements

tubes, for which the minimum detectable 40 key. These measurements have mostly higher than those mentioned above, namely

77

can

exponential

spectrum

Ilwain interpreted his rocket measurements indicating a monoenergetic flux of electrons 6 key.

stage

hitherto

in an

in the

exp (-E/b), Stilwell, but

present

it possible to draw some effects of the precipitated

expressed

value,

form _ 1960;

at the

spectra energy

have

been

for

pre-

value

of

made

with

electron energy given e-folding between Z0 and

is values 45 kev.

a

(Davis et al. 1960; McDiarmid et al. 1960; et al. 1963; McDiarmid et al. 1963; O'Brien et al. (1963) the values 42

found

from

within

measurements

this range

were

O'Brien et al. 1962; and Taylor, 1964).

during grouped

only

in two

some

Z0

classes,

Mann Mann

orbits

Z5

that

+ 5 key

and

+ 3 key. The

balloon

general,

give

energies

in the

Enemark,

measurements

spectra range

1960),

observations

better

with

seems

crease

fast below

type

the

dayside

with

low

lower

Of

that the

1 kev,

which

reported

riometer

down

special

to e-folding

are

found

and to fit the

of precipitated

electrons

et al. 1963,

1964c;

Evans

(O'Brien

spectrum, means

and

Taylor,

in general,

that

1964).

does

it is not of the

not

in-

power

energies.

et al. (1964)

located

in

spectra.

(Sharp

in aurora

on the nightside

multifrequency

Lerfald

also,

e.g., Anderson

often

measurements

height

et al. (1964c) than

(see

exponential

reported

altitude

corresponding

spectra

than

been

probable

at these

Sharp

law

km

showed that there is generally not very much energy This is also evident from observations of the lumi-

It therefore very

power

have

distribution

law

mentioned

key

first direct

energy

et al. 1964). They flux below 1 key. nosity

flat type,

20-45

although

the

1 key

at 30-35

of a fairly

somewhat

Recently below

of x-rays

interest

to which

atmosphere

are

earth.

measurements

according in the

a significantly of the

the

harder This

spectrum

of auroral the

in the

statistical

data

by

ionization

than

on

agrees

absorption

absorbing day

on

observation

in the

electron

is

night.

precipitation,

published recently. As mentioned earlier the precipitation is most intense near the auroral zone. O'Brien (1964) found an average flux of 4.10 s electrons/cm

2 sec

in the precipitation

tude

of 65 °.

Injun

1 had

above

about

1 key

(O'Brien,

that the

a CdS

detector, 196Zb).

flux of 4.10 s electrons/cm

was associated with an energy E >_ 1 kev. These data should about

three.

in the range e-E/S ._

been

Using 1-40

electrons

these key (cm

For the energy obtained from

et al. (1963).

While

can

O'Brien 2sec

values

be

deduced.

an

equivalent It is found

invariant

electrons Taylor

(1964)

greater

than

stated 40 key

electrons to a factor

electron to be

lati-

of energy

n(E)

of of

spectrum = 7.8 • 107

key) -I .

values 40 and Z50 key the Alouette measurements the

and

of energy

at an

flux of 4 erg/cm 2 sec for be considered as accurate

two

2 sec

cone

measuring

flux

above

40

78

key

similar average reported by had

its

maximum

fluxes have McDiarmid at

an

invariant latitude of 65 degrees, the flux above 250 key was maximal at about 60 degrees. McDiarmid et al. (1963) did not present any details for the latitudinal variation of this latter integral flux. By applying a rough correction factor of 0.i for the latitude variation of the average flux above 250 key from 60 to 65 degrees invariant latitude the following approximate equivalent spectra for the energy range 40-250 key can be derived for two ranges of magnetic activity in the auroral zone, if isotropy is assumed for the upper hemisphere: Kp




4:

n(E)

=

l .Z

n(E)

= Z.4

•

10 4

e -E/41

electrons

(cm 2 sec

key)-1

•

l0 s

e -E/3°

electrons

(cm

kev)-1

2 sec

P

(cf.

Hultqvist,

large

and

As

1964b). the

mentioned,

There

is

with

O'Brien,

1964). (O'Brien,

given

above

fluxes.

With

sity

produced defined

not

identical

for

electron

the

the

average only

Observed

The

or from ditions

Into of

is

much

in

passing

launchings with no auroral

in

measured

energy been

on

Spectra

less

made

be

fluxes

are

electron

den-

density of

the

shown

the

measured may

electron

is

averaging

is

ionospheric

that

the

average

can

satellites

of

spectra of

integral

method

values

precip-

be

expressed

(Hultqvist, are

available

average

flux

1964b). one to

has

these

ex-

Protons

Atmosphere

observations

of

than

through

flux

of

averages

electrons

relation for done above.

Energy the

be

significant

average

measuring

precipitated

1963;

equivalent of

the

this

however,

which al.

number

average

and

integral

and

number

atmosphere observed

has

Fluxes

Precipitated

the

fluxes

experimental as

can,

by

integral two

to fit a two-parameter perimental data,

3.

it

produced

The

process, made

the use

in

no

flat.

variable.

intensity

average is

influx.

averaging

instance,

density

Since

particle

be

a large

l0 s the

interest

very et

the

which

whether

the

averaging

with

on of

to on

too too

steepness

McDiarmid

or

over

a factor

when

the the

averaging made

the

seems

angle

than

are

in

1962;

there

questionable

use

by

al.

probably

rather

electrons

pitch

been of

also

to

by

absorption, in

is

values

then

has

a variation It

best

hand on

is

steep

variation et

The

based

too

precipitated

other

1964). are

questioned. the

the spectrum

correction

thus

latitude (O'Brien

On the

latitude are

of

important

latitude

of

itation

spectra

an

increases

applied

spectra

the also

dependence

The

resulting

that

protons for

aurora

under information

or quite

their

electrons. close

disturbed available,

79

on

way Some

to

distinct are

down rocket auroral

upper atmosphere collected in

into

the

results forms, Table

conZ.

While case

electrons

of no.

flights

la, protons

ib,

electrons

were

c,

and

were

amounts. and

show.

This

may

possibly

the

atmosphere.

field lines the

and

Z in which of the

greater

of that

say,

could,

flux,

is as

the

spread

basis

mostly

of

ground

diffuse

and

standard

ground

tribution

of

There

are

two

relations

between

discussed

here,

(1964). on

that

i/5

of the

Dalgarno,

I/5

of

normal

the or

l

energy

more,

as

the

to

for

height

Rocket

measurements be

Electron

and

those

to compare

flux

the

on

electron

these

things

emissions

of

are with

the

height

dis-

valuable.

(1960) results

and

of the

emission

their

aurora.

protons

determination

reported photon

and

ordinary the

Precipitation

of McIlwain

energy

measurements.

than

unsuitable

possi-

heights

judge

hydrogen

radi-

about

same

Injun

surface

would

in

energy

auroral as

difficult

auroral The

an

the

above

measurements

did not use the

any

filter,

transmission light was

to an emission fraction

before

of Tables

quantitative

which and

will be

O'Brien

with

what

and

Taylor

is expected

grounds.

Mcllwain over

also to the

out

the

the

precipitation namely

It is of interest

theoretical

grated

direct

basis

larger

seems

Between Aurora

in

that

generally

locked

1964}.

especially

emissions

Relations Emission

Taylor,

well

observations,

hydrogen

in

electron

any constituent

with

the

a much It

therefore

found to have

measured,

with

the

weak,

techniques.

the

Quantitative Photon

on

emissions over

an

spread

not measure dominant

and

above

quite

above.

up

of magnitude,

protons/cm2sec

excluded

out

were

orders

Injun 3 did were not the

stopped be

seems

no

emissions

In all cases

electrons/cm2sec

hydrogen

mentioned

protons

were

it is not

be

In the

and

flux.

many

be be

however,

generally

4.

were

thus

taking

1958).

(O'Brien

there

expect

could,

1 and

ions)

atom

in the

volumes.

hydrogen

flux may

two

energy

as

would

would

They

and

about

were

not

protons

one

was

Injun electrons

however,

Such

on

as

a neutral

particle

penetrability

there

to protons

As

(Shklovskii,

the proton

a given

kev,

the

heavier

the

form

penetrated

precipitation that

auroral

larger

was

due

electrons

The satellites in which the

bility 40

both

electrons

than

ation

and

be

atmosphere

flux

proton

the

much

form

(and/or

character

outside

reaching

event

The

within

over

auroral

protons

diffuse

magnetic

only

found

no

recorded,

appreciable

well

were

d, when

wide

spread

observed

rate is fairly

1964)

and

curve {}

h.3914

of about

A,

but

measured

of the the

measured

3 kilorayleigh

arbitrary, is probably

but

8O

photon

flux If we

by

reasonable less

than

inteassume

flux corresponds

at this wavelength.

it seems

in error

the photon

photomultiplier.

(cf. a factor

The e.g. of Z and

1/2, respectively, measured electron sec

if the

for an ordinary flux corresponds

spectrum

obtained

auroral-zone to an

was

energy

extrapolated

aurora. flux

McIlwain's of 20 erg/cm

to E = 0.

Thus,

(1960) 2

the

O

resulting electron energy rate is 7 ergs crn -2 sec O'Brien

and

of Z (+_.5) kR auroral zone.

Taylor

average

sec -landan

average

values to get

have

ergs

the

sec'l

zation

as

energy

this.

kR.

(1963)

It has been cross section

cross

section

of

k3914

average

A emission

k3914

_

flux

40

to a factor with that

intensity

key

from

in the gave

of 4.

this

the is

1 kev

down

does one processes?

expect

Dalgarno

shown for the

to E = 0 and spectrum, give 2.5

in measurements

on the basis Omholt (1957,

(1964),

among

others,

of existing 1959) Chamberhave

dis-

at

least

up

to 200

ev

energy

and

has an energy of 3.2 into 3914 A radiation

_ sec,

(1964) has used find the energy agreement (1960) the

if the the flux

between and

O'Brien

uncertainties

ev, is

the

has

over the whole energy pairs are produced expended by fast electrons

in nitrogen per electron ion pair is 35 ev (at least for energies a few hundred ev; it is assumed the figure is correct down to zero we find that 50 x 35 = 1750 ev is dissipated per 3914 _photon.

erg/cm

In would

by Stewart (1956) that the ratio between + _3914 _ band of_I 2 and the total ioni-

is constant

energies of the fast cies must decrease 1964). 1 kR of 3914

,

agreement.

the value 0.02. Assuming that this value is true range of interest, one finds that 50 electrons-ions for each 3914 /_ photon. Since the mean energy

each photon is converted

-2

sec-'

of about three. of Mcllwain one

uncertainties

a good

10Scm

cm -2

Using the =_l_l"-'_lv,_e,,_-+_,_,,,,_,,_,_+_1 E > 0. Thus the Injun 3 results

Considering

and

above

E _>1 kevofabout4ergs

spectrum

flux per kR the emission

Rees

for

accurate comparable

of evaluation,

energy about

(1961),

cussed excitation

per

method

What knowledge lain

the

unit

an

electron

the total energy flux. 5 ergs cm -2 sec -1 for

cm "2

and

reported

flux

they consider a value directly

per

of the latitude distribution i.e. before the electron measurements

of the

energy

to extrapolate

evaluate we find

(1964)

at the maximum As mentioned

a corresponding which order

flux required per kR.

the efficiency 1.80" 10 "_

down to energy) Since

with which energy When the initial

electrons fall below perhaps 100 ev, these efficiensharply (Dalgarno and Griffing, 1958; Dalgarno, O Aphotons corresponds to an energy influx of Z.8 efficiency

figure

1.8"10

-3

is employed.

value 1 • 10-3. requirement

With this conversion to be 5.1 erg cm -2

these

and

and in the

values Taylor analysis

(1964) are

the is taken

experimental much into

better acco_ut.

Dalgarno

efficiency sec -1 per ones than

we kR.

The

of McIlwain expected,

when

The any

total

energy

lain,

efficiency

1961).

only

while

Taylor,

1964).

5.

Relation

of

into

about

the in

ago,

was

large

storage

belt, and

by

in the

has

loss

only

been

(196Zb)

outer

hours.

Similar

x-ray

measurements

(cm I00

zone

are

precipi-

(cf.

than

I000

O'Brien

et al. (1962)

and

at the beyond

in the field tube

same L

e.g.

the particles

in half

et al. orders have

196Z, an

used

a second,

seconds.

82

burst

but

by

but

in

the

Injun

i.

He

of electrons evaluated

et al.,

1964).

above

observed

in

from

Anderson,

of magnitude been

up

electrons

empty

and

1 fluxes

1964).

stopped

been

1962

Winckler

electron

have

of Injun

observed

also

investi-

of x-ray

Anderson,

drain

have

2 sec)

Laughlin,

would

as

assumed

the

of the trapped

_ 2 would

several

ergs/cm

results

was

of

radiation.

through

studies

source

ob-

in the

to be

of the trapped

rate

Winckler

rates

processes

is necessary

recently,

lifetimes

recorded

2 sec) -I , a flux which

independent

lifetime

as, for particles

perhaps

et al., 1962;

the through

plasma,

of trapped

of balloon

years

from

magnetosphere

number

that the

two

dumped

solar

of the measuring

the

rates

the

the

trapped or

the precipitation

a number

average

precipitation (more

particles

of

(O'Brien

the

one

to allow

existence

(Winckler

operated

in

changed

1964)

and

to replenish

the

estimated

that the

Winckler

a value I%

that

were

by

of which

belt assuming

a few

1961;

and

completely

through

found

et al.

electrons

prevailing

The

large

required

atmosphere

mechanisms

average

the

particles

weak

(1962b,

also

radiation

Sometimes

Outer

of

(cf. Chamber-

towards

elsewhere

caused

the occurrence

O'Brien 3 and

lower

outer

point

particles

effects

for understanding

O'Brien the

into photons basis

measurements

the

was

precipitated

acceleration

picture

and

which

disturbances.

with

and

Injun

auroras

sufficiently

radiation

gations

to

trapped

magnetic

injection

and

the

energetic

to be

case

rocket

3 results

between

belts,

that

to occur

This

in

radiation of

the

in any

his

Injun

relations

of disturbing

thought

served

the

roughly

example

from

energy

on theoretical

Electrons

atmosphere the

the influence

was

particle I%

Belt

idea

radiation

found

Precipitated

Radiation

about

preliminary

and

tated

to be

McIlwain

0.2%,

The

of converting

is expected

the

(Krasovskii 196Z).

Thus

1011

electrons

reaching

the total energy yet it persisted

of trapped for

about

O'Brien creases

(1964)

when

would

be

expected

atmosphere. and

change

Taken are

such

of

be a

than

10%

energy tron

one when

above flux

this

new

above

of

trapped

of

radiation

diminishing,

were

simply

seems

to

in-

which

dumped influence

into

the

precipitated

can it the

act

with not

evidence

full

is key

aurora

more

strength the

changes

three

83

due

the whole

Mev

trapped the

orders

This (in electrons electrons

precipitated of

simply

spectrum.

ionization into

quickly of

40

.L-._.=,.L_.e

ionospheric

involved.

very

of

be

ob-

above

in the geomagnetic

electrons

flux for

and

than

not

over

and be

i. 5 Mev

demonstrates

of trapped

a hundredfold, is

u_e,_j:xy .......

change

than

is

precipitation

of energy

could

active

must

simultaneous

greater

a decrease

be

dumping

should

key 40

through

would

(< i0%)

of electrons

precipitation

mechanism

and

that the precipitation

significant

of energy

produce

simple

that

no

burst

point

which by

40

was

that the

acceleration

second)

flux

demonstrated

of a strong

together,

An

has

There

a mechanism

produced

phere.

particles

flux of electrons

electrons

not

must

(1964)

of the mirror

precipitated

the instead

mechanism

demonstrates

since

that place

simultaneously,

middle

to a lowering field,

acceleration

in the

This

shown

trapped

dependent.

in the

key.

the

O'Brien

energy

served

also

takes

particles

Finally, or

if

An

trapped

highly

has

precipitation

magnitude.

the

atmos-

mechanism a fraction more of elec-

Table Precipitated

1 Electrons

60_R

84

Table

Flu,

(ol.o+,

I (Continued)

Villbllmm

m, ot_l_we) plot,

Ho

o+ mol.. 4_.m+b.

R,_ _l_c_e_

_ I_2_

_

0t_

I+(E_

_Mt

151_ UT

_p

.+._l+ ) _130 UT

(cm2 l_

2105

T_

,tw) -I

_l

1/4 _

I/3

oflr_ clrcll;

i.

C_ml.

o(

wlm

N (E) (-E/25 * 5) _d Hp

I

with d_,_b

N (E).._p (-E/_*3)

E>

(1963)

10k_

'

iK E>

,+.@'1 10_..

A_

_lu.

_

(-E/4) E> 10k+v

Aln_llk+tlield I_I ,mell. il

0721 UT LT-_

l+me

+O_

_k,+

_,poml w._,;ol

_

_+.ol. i+_cu

2+6.10_ (cm_ ,_ +or E > 250 k..

,_)-I

c_-

E_+v.

_-

m

,l_+m.m A_ °

_ 0+

_

N(>E)_4 .-E/_o .I

K_ • 4" o

+10 a (+.,_

A =65"

_

O+3 _g (_.Z +_)-I

N(>E) _4.4. 1011.E-_ 9 .I

,_,. k_)-I

(_o+ 40
4 ÷

E < 2_0

k.v)

•_-+

_

E > 4O k_

=m-_

s_ +1 Iw

,_ E)=I+4+ 10+ £-1_ ._.

I%

_p+t

oi,

M,o_. 10 | +l/cm 2 .+c s,_

,, .I+

(I_)

M+_. olm_.

6+10+ .I/era

iK-I

I
-_

v,=

_q

,..,.o.

zR

,

I

•

,

_.-= '°"

I

*

:

I

•

"

•

|

ii

O

|

':'

':;1!

, ,,,,

";'1

!i

II • " - .,I:." ' :. t .;.i: •

.._

:

ill

|

"I'::;" 1

'

I ,:,"

: .l

• "'i

I '

'

/

42

44

41

L-/ DETECTA_: IUTY 55"

34

a8

14

S

2

I

THRES,HOLD

60"

65"

70"

75"

INVARIANT LATTITUDE A (L COS2 A • I) o

Fig. aged

4.4-Intensity over

4

of 3914 sec

A auroral

at half-integral

about fifty passes of Injun 3 early O'Brien and Taylor, 1964.)

light values in 1963.

averof L in (After

I

107!-

INJUN ]][ COMPARISONOF LATITUDE PROFILES OF PRECIPITATED ELECTRONS El

mq-i If_s :r

,%

" ,o.-i!1

J _'_'_

,_

-

II

,,; . : I1

#

_,o- _ il _ , _

li

_1o31--

"J"

_

It M

"

! /v_ /

"_,.,_,_u:r.uulx. _, im

-

I ;I

_

,_-