JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 90, NO. A7, PAGES 6395-6407,JULY 1, 1985
Long-Term (Solar Cycle) and SeasonalVariations of Upflowing Ionospheric Ion Events at DE 1 Altitudes A. W. YAU AND P. H. BECKWITH! Herzberg Institute of Astrophysics,National ResearchCouncil Canada, Ottawa, Ontario W. K. PETERSON AND E.G.
SHELLEY
LockheedPalo Alto ResearchLaboratory,Palo Alto, California A statistical analysis is presented of the long-term variations of upflowing ionospheric ion (UFI) occurrencemorphology in the high-altitude (8000-23,300 km) auroral and polar cap ionosphere,using data from the Dynamics Explorer 1 Energetic Ion Composition Spectrometer from 1981 to 1984. The studyis basedon over 100,000data samples,eachconsistingof pitch angledistributionsof H + and O + intensitiesat 0.01-1, 1-4, and 4-17 keV/e. The data sampleswere grouped into 91-day intervals (seasons). Within each interval they were sorted into altitude, invariant latitude, magnetic local time, and magnetic activity(Kp index)bins,and the occurrencefrequencyand intensitycharacteristics of H + and O + UFI in
the respective binsweredetermined. The September1981to May 1984periodcoincides with the declining phaseof solar cycle 21, when the solar radio flux at 10.7 cm, Fxo.7,decreasedfrom a high of 222 ( x 10-22 W m -2 Hz -x) in September1981to a low of 93 in November1983.The observedoccurrence frequency,intensity,and angularcharacteristics of O + UFI exhibitedmarked variationswhich correlate with variations in the solar radio flux (and which envelop those of magnetic activity and seasonal origins).In contrast,the H + UFI morphologydid not displayany observablelong-termvariations.At both quiet (Kp _80
Low High Low
(150) C
0900-1500
High
(193) 278
Invariant Latitude,deg
373
3929
(478)
(254) (133) 2046 564
187 16
332 170
866 906 269 338 156
416 268
137 108
96
3450 4278 2625 1925 2194
(25) 410
(46)
(142) 2354
(259)
(133)
672 206
509 217
The two figuresin eachMLT or invariantlatitudeentryare the numberof low- and high-altitude(8000-16,000km, 16,000-23,300 km) data samples,respectively. Figuresin parentheses, whereindicated,are corresponding numbersof samplesin the oppositehemisphere. *Read the period as,for example,day 209, 1981,to day 309, 1981.
1-4, and 4-17 keV/e) and nine pitch anglebins of 20ø each.By taking advantageof judicious energysettingselectionsin the respectiveinstrumentmodes,the averagedcountsper sample over the selectedenergystepsin a given mass-energyangular bin, C(m, E,/•), is approximatelyproportionalto the integrated ion flux l(m, E, l•). The angularbins are approximatepitch angle bins in that the pitch angle values used in the data sorting are only approximate and are typically in error by
the four MLT sectors(night:dawn:noon:dusk) are approximately 1:0.9: 1.1:0.6 and 1:0.6: 1.0:0.2, respectively.Likewise,the ratio of data samplesin the three ILA regionsare
1: 1.8:1.5 in A, comparedwith 1: 1.6:2.1in A'. This similarity greatly facilitatesdirect comparisonbetweenUFI occurrence morphologywithin respectiveseasonpairs, as it minimizes relative statisticalbias betweenthe two periods of a season pair due to nonuniformdata sampling. •-, 10 ø or less. Overall,data werefairly evenlydistributedin termsof magThe full data setwasdividedinto 12 subsetscoveringspecif- netic activity. The period September1981 to May 1984 was ic time periods (seasons).Within each subset the summary relativelyquiet magnetically.In the period September1981 to data for each of the six mass-energychannelsabove 8000 km January 1983, Kp was __6-- in 41%, 54%, altitude and 56 ø invariant were sorted into 4096 fourand 5% of the time. The data distributionsin the three Kp dimensionalunit bins (z, ILA, MLT, Kp): eight 2000 km alti- regimes were 42%, 53%, and 5%, respectively.The corretude bins by 16 2ø invariant latitude bins by eight 3-hour spondingKp distributionin the period February 1983 to May magnetic local time bins by four Kp index bins. The MLT 1984 was 43%, 53%, and 4%, respectively.The data districoordinate was defined with respect to the magnetic north bution was 45%, 51%, and 4%, respectively. pole (78.8øN, 289.25øE).The ILA coordinate up to •85 ø was
derivedusingthe ILA = arccos(1/L1/2)relationshipand the latest MAGSAT model; data in the ILA > 85ø regionwere all grouped into the highestILA bin. Data in a given year are groupedinto one 92-day and three 91-day periods centeredat the spring equinox, summersolstice, fall equinox, and winter solstice, respectively.Over 100,000 data samplesacquired between September 15, 1981, and May 31, 1984, were included in this study. Table 1 summarizesthe altitude, MLT, and ILA coveragesin the respective data periods.In A, data were available only from day 81258 on; in F, they were available up to day 84152. Data coveragewas most extensivein the early periods(A, B, and C) and relatively scanty in the late periods (E' and F'). Also, within a period, coverageis typically concentratedon two of the four MLT sectors;in periodsD and D' there were hardly any data in the night and dawn sectors(2100-0900 MLT) and at high-altitudepolar cap (> 80ø invariant).However, the relative distributionof data coverageis similarbetweenrespective seasonpairs. For example,in A and A', data coverageratios in
ANALYSIS
Following paper I, UFI eventsare definedin terms of the pitch angle characteristicsof the ion flux distribution l(rn, E, /•) and are referredto as follows:(1) 100ø-180ø ions, (2) 100ø160ø ions, and (3) at the low-energy (0.01-1 keV/e) channel only, 80ø-100ø ions. Type 1 eventsare UFI with peak flux in pitch angle bins 6 to 9 (1 to 4 in southern hemisphere events).
Type 2 eventsare a subsetof type 1. Type 3 eventsrepresenta realistic estimate of transverselyaccelerated ion events. No distinction
is made between ion beams and
> 160 ø conics in
type 1 (in the conventional sense), since the data were averaged over 20ø pitch angle bins, the pitch angle calculations were approximate, and the actual measurementsdid not always extend to 180ø. However, the differencebetweentypes 1 and 2 provides an upper limit of ion beam occurrencefrequency.
Each 96-s distribution in the data base within bin (z, ILA, MLT, Kp) is countedas a sample.A sampleis classifiedas an
YAU ET AL.' SOLAR CYCLE VARIATIONS OF UPFLOWING IONS
A z 80 ø I
I
I
!
Kp80 ø
invariant,left panels)and (b) auroral latitudes(56o-80ø invariant,right panels).Top panels:H + data; middlepanels:O + data; bottom panels: year, season,and hemisphereof sampled data, mean solar radio flux of season,and mean Kp value of data samples.Left to right panels:seasonpairs A-A', B-B', and F-F' in Figure 3a; A-A', B-B', and E-E' in Figure 3b (see Table 1).
event if the flux in the peak pitch angle bin l(m, E, Pmax) exceeds(1) a specificthresholdlthrcs(m, E) and (2) the fluxesin the opposinghemisphericbins by a least ltr. Within each bin the occurrencefrequency of a UFI type x in mass-energy channel(m, E) is definedby
f(z, ILA, MLT, Kp; m, E, x) =
n(z, ILA, MLT, Kp; m, E, x) N(z, ILA, MLT, Kp; m, E)
ing f(z, ILA, MLT, Kp; m, E, x) over all z, ILA and MLT resultsin the averaged occurrenceprobability f(Kp) in a given Kp bin. Likewise, averaging over z gives the corresponding invariant latitude-local time distribution f(ILA, MLT, Kp). Note that the average frequency over a limited range of a particular dimension (e.g., invariant latitude) may be determined by restrictingthe summationsin (3) and (4) to sampled binswithin the specifiedrange. RESULTS
where N is the number of samplesand n the number of type x
In Figure 3 the average occurrencefrequencyof a specific UFI event type in a given 91-day period over a specificina(z,ILA, MLT, Kp; m, E, x)= If(1 --f)/(N -- 1)J•/2 (2) variant latitude range is computed. Figure 3a shows the averagedquiet time (Kp _ 80ø invariant) as j, k, and I is computedusingthe expression a function of peak ion flux for periodsA and A' (northern fall equinox in 1981 and southern fall equinox in 1983), B and B' j,k,l Ij,k,l (northern winter solsticein 1981 and southern winter solstice in 1983), and F and F' (southernsummersolsticein 1982 and The standard error is northern summer solsticein 1984), respectively.In all of the figures, f(> I) denotes the occurrencefrequency of all events (4) tr(i;m,E,x)= • tr(i,j, l; m,E, x)2 exceedingion flux I. Figure 3b compares the corresponding ,k,l I frequenciesat auroral latitudes (56o-80ø invariant) between periods A and A', B and B', E and E'. In each figure, triangles where j, k, and I can be any of the four dimensionsz, ILA, MLT, and Kp' i denotes the remaining dimension, and the denote data in the unprimed (early) periods; the circles are summation • is overthe sampledbinsin the unwanteddi- data in the primed (later) periods. The year (Yr), season(Sn), mensions(thosefor which N(i, j, k, l; m, E) > 1). Thus averag- and hemisphere(Hs) of sampleddata in each period are given events. The standard
deviation
estimate is
f(i;m, E,x)=• f(i,j,k,l;m, E,x)/•
(3)
6400
YAU ET AL.' SOLARCYCLE VARIATIONSOF UPFLOWING IONS
a, Sep 81- Jan 83
56ø-
107 fluxes.As in Figure 1, the differentcircle the mean occurrencefrequencydue to data sampling nonunitypes are intended to indicate the different seasonsbetween successiveperiods in the series.The solid circles symbolize winter (periodsB and B'); the open circles,summer(F and F'). The semi-opencircles on the left denote fall (A and A'); the ones on the right denote spring (C and C', E and E'); and the ones in the upper hemispherecorrespond to periods of equa-
formity should not be a problem. The solar fluxes in the two periodsare comparable,being 134 and 126, respectively.Yet,
torial apogeeand comparable data samplingin both terrestrial hemispheres(D and D'). Figure 8f shows the monthly mean 10.7-cm solar radio fluxesat 1 AU in the 91-day periods. A number of trends are apparent in Figures 8a, 8c, and 8e.
stice.
At both quiet and activetimesthe O + UFI occurrence frequency displaysa continual trend of overall decrease.The
decrease is mostapparentamongthe moreintense(> 107 flux) events.Superimposedon the long-term decreasingtrend are short-term increasesat periods E, F, E' and F'. In contrast,no
the O + frequencyin the summerperiodis significantlyhigher than the correspondingwinter period value. On the basis of
the two comparisonsthe data appear to indicatea seasonal variation of O + UFI
occurrence in favor of the summer sol-
SUMMARY AND DISCUSSION
A statistical analysis has been presented of the long-term variations of upflowing ionosphericion occurrencemorphology in the high-altitude (8000-23,300 km) auroral and polar cap ionosphere,using data from the Dynamics Explorer 1 Energetic Ion Composition Spectrometerfrom 1981 to 1984. The study was based on over 100,000 data samples,each con-
long-termtrendof decrease is apparentin H + UFI. The long- sistingof pitchangledistributionsof H + and O + intensitiesat term averagedH + occurrencefrequencyin the 1981-1982 0.01-1, 1-4, and 4-17 keV/e. The data sampleswere grouped period is comparableto the 1983-1984 average.Also, the two periodshave similar trendsof apparent short-termvariations. Since the data in individual 91-day periods fall into a particular season(except for periods D and D' (see Table 1)), it may be tempting to interpret the apparent short-term variations in Figure 8 as seasonalvariations. However, such an interpretation is complicatedby the relative bias of the computed occurrencefrequenciesin different periodsdue to relative nonuniformity in MLT-invariant latitude coverage between periods.In particular, the coveragein periodsD and D' was extremely nonuniform. Consequently,the computed frequenciesfor these periods are more biased relative to other periods and may not be compared with the corresponding data for their neighboringperiods; they are includedin the
into 91-day intervals (seasons).Within each interval they were sorted into altitude, invariant latitude, magnetic local time, and magnetic activity (Kp index) bins, and the occurrence
frequency and intensitycharacteristics of H + and O + UFI in the respectivebins were determined. The September1981 to May 1984 period coincidedwith the decliningphaseof solar cycle21, when the solar radio flux at
10.7cm,Flo.7,decreased froma highof 222( x 10-22 W m-2 Hz-1) in September1981to a low of 93 in November1983. The observed occurrence frequency, intensity, and angular characteristics of O + UFI exhibited marked variations which
correlated with variations in the solar radio flux (and which envelop those of magnetic activity and seasonalorigins). In
contrast,the H + UFI morphologydid not displayany observ-
figure only for completeness. In the caseof H + the lower able long-termvariations. frequenciesin periodsC and C' are attributed,at leastin part,
At both quiet (Kp _n(O)t• l,o+
Lt.I
summer
•---
SOLAR
solstice
w•nter
MINIMUM
SOLAR
solstice
MAXIMUM
Fig. 9. Schematicdiagram depictingthe observedsolar cycle and seasonaldependences of upflowingionosphericion
occurrence morphology.The sourceregionsof O + and H + UFI are indicatedby the shadedareas.Increasedintensity (darkness) of shadingdepictsincreasein occurrence frequency. O + UFI occurrence frequency increases with solaractivity and in summerrelativeto winter; the sourceregionconcurrentlyshiftsto higheraltitude.In contrast,H + UFI do not displayany significantvariationswith solar cycleor season.O + is more abundantnear solar maximum.Near solar minimum,H + and O + arecomparablein abundance.
he found that the occurrenceprobability of TAI peaked at the winter midnight sector.Yet, from the ISIS 1 data above 2700 km altitude, Klumpar found that the majority of events occurred in the daysideand near summersolstice.Klumpar and coworkers [Ungstrup et al., 1979] postulated current-driven electrostaticion cyclotron instability as the sourcemechanism of the observedTAI and attributed the apparent contrast in local time and seasonal dependencesof observed TAI occurrence
at the two
altitudes
to variation
of the lower
TAI
sourcealtitude resulting from seasonaland diurnal variations of the ambientdensity.Specifically,in the winter and nightside ionospherethe ambient electron density is low, and the theoretical threshold for electrostaticion cyclotron instability is exceededat lower altitudes for a given current density (assuming that the ambient plasma is the current carrier). In the illuminated summer and dayside ionosphere the plasma density is high, and the onsetfor the instability is shiftedto higher altitudes,and hencethe TAI sourceregion is shiftedto higher altitudes in the summerand in the dayside. A. G. Ghielmetti et al. (unpublished manuscript, 1984)
active times, for which the observedsolar activity dependence in the DE 1 data is strongest.The factor of 3 increaseof TAI occurrencebetween 8000 and 14,000 km (Figure 5) at solar maximum
and the increase in conic abundance
in the 8000-
23,300km rangeindicatean upwardshiftin the perpendicular accelerationregion. Since, as noted above, the average UFI energy increaseswith altitude, the present result suggestsa corresponding decrease in both overall occurrence and averageenergyof UFI below 8000 km. In view of the > 500 eV energythresholdof the S3-3 ion compositionspectrometer, a several-fold
decrease in observed UFI
occurrence
at solar
maximum would likely result in the S3-3 data. A. G. Ghielmetti et al. interpreted their observation of decreasedUFI activity below 8000 km at solar maximum in terms of an upward shift of the accelerationregion. The present result supportstheir interpretation. The existence of secular variation
in the level of auroral
activity has been known sincethe early 1700's.Siscoe[19803 reviewed catalogs of oriental and European auroral records coveringthe period from 480 B.C. to A.D. 1700 and inferred found a factor of 5-10 decrease in observed UFI occurrence the existenceof a quasi-80-year periodicity in the recorded above 500 eV/e below 8000 km altitude during the rising auroral frequency.Siscoealso reviewed the early works of phase of the current solar cycle (from 1977 to 1979), when Harang [19513 and Loomis [18733, which independentlyesEl0.7 increasedfrom 80 to 195. The observedoverall decrease tablished the systematic correlations between auroral ocwas accompanied by an increase in conic abundance. Their currencefrequencyand the ll-year sunspotvariations in the result may be qualitatively understoodin terms of the present nineteenthcentury.Deehr 1-19833analyzeddata setsof auroral observation of increased TAI occurrence and conic abundance heightmeasurements from differentperiodsbetween1910 and at DE 1 altitudes during solar maximum. Note that the S3-3 1970 and found the altitude of aurora to anticorrelate with the analysis is limited to higher-intensity and more energetic recurrenceprobability index of geomagneticstorms.Basedon events(> 500 eV/e and > 2 x 106 cm-2 s-1 sr-• flux) at the anticorrelation betweenthe index and the 11-year sunspot
YAU ET AL.: SOLARCYCLE VARIATIONSOF UPFLOWING IONS
cycle,Deehr concludedan 11-yearcycle of auroral height variation, peaking at solar maximum. Feynman and FoutIere 1-1984]spectral-analyzedone of the auroral catalogs(the medieval set) reviewed by Siscoe and establishedthe quasi-80year period noted by Siscoe1-1980]to be 88.4 years.Feynman and Fougere concludedthat the 88-year auroral variation is related to the secular variation (the "long cycle") of the sun and arguedthat the changesin solar outputs connectedto the long cycleare differentfrom thoseassociatedwith the 11-year cycle. On the basisof the present and earlier data it is reason-
6407
Lennartsson,W., E.G. Shelley, R. D. Sharp, R. G. Johnson,and H. Balsiger, Some initial ISEE-1 results on the ring current compositions and dynamicsduring the magnetic storm of December 11, 1977, Geophys.Res. Lett., 6, 483, 1979. Lennartsson, W., R. D. Sharp, E.G. Shelley, R. G. Johnson, and H. Balsiger,Ion compositionand energy distribution during 10 magnetic storms, J. Geophys.Res.,86, 4628, 1981. Lockwood, M., Thermosphericcontrol of the auroral sourceof O + ions for the magnetosphere,J. Geophys.Res.,89, 301, 1984. Lockwood, M., and J. E. Titheridge, Ionospheric origin of mag-
netospheric O + ions,Geophys. Res.Lett.,8, 381, 1981. Lockwood, M., J. H. Waite, Jr., T. E. Moore, J. F. E. Johnson,and C.
able to think of the observed variations of UFI activities as an R. Chappell,A new sourceof suprathermalO + ions near the daysidepolar cap boundary,J. Geophys.Res.,90, 4099, 1985. integral part of the solar cyclevariation of the overall auroralLoomis, E., Comparison of the mean daily range of the magnetic magnetosphericsystem. declination and the number of auroras observedeach year, with the In conclusion,the observedsolar cycle and seasonaldepenextent of the black spotson the surfaceof the sun, Am. J. Sci., Ser. 3, 5, 245, 1873. dencesof upflowing ionosphericion occurrencemorphology Lundin, R., L. R. Lyons,and N. Pissarenko,Observationsof the ring are summarizedschematicallyin Figure 9 and are as follows. current compositionat L -- 4, Geophys.Res. Lett., 7, 425, 1980. 1. The accelerationaltitude of O + UFI is modulatedby Lundin, R., B. Hultqvist, E. Dubinin, A. Zackarov, and N. Pissthe atmosphericscaleheight, which increaseswith increasing arenko, Observationsof outflowing ion beamson auroral field lines solar activity (EUV flux). at altitudesof many earth radii, Planet.SpaceSci.,80, 715, 1982.
2. O + UFI occurrence frequency(and henceO + outflow) Moore, T. E., Modulation of terrestrialion escapeflux composition (by low-altitude accelerationand charge exchangechemistry),J.
increases at solar maximum.
Geophys.Res., 85, 2011, 1980.
3. The sourceregion of O + is shifted upwardsat solar Moore, T. E., Superthermalionosphericoutflows, Rev. Geophys.,22,
maximum.
4.
O + UFI
264, 1984.
occurrence exhibits seasonal variations
favor of the summer solstice over the winter
in
solstice.
5. There are no significant solar cycle or seasonalvariations in H + UFI occurrence and source altitude. 6. UFI is O + dominant near solar maximum
and com-
parablein H + and O + near solarminimum. Acknowledgments. This research was partially NASA
under contract
NAS5-25694.
The authors
thank
supported by A. G. Ghiel-
Peterson, W. K., R. D. Sharp, E.G. Shelley, and R. G. Johnson, Energeticion compositionof the plasma sheet,J. Geophys.Res.,86, 761, 1981.
Sharp, R. D., D. L. Carr, W. K. Peterson, and E.G. Shelley, Ion streams in the magnetotail, J. Geophys.Res., 86, 4639, 1981. Shelley,E.G., Circulation of energeticions of terrestrialorigin in the magnetosphere,Adv. SpaceRes.,in press,1984. Shelley,E.G., R. G. Johnson,and R. D. Sharp, Satellite observations of energeticheavy ions during a geomagneticstorm, J. Geophys. Res., 77, 6104, 1972.
metti for valuable discussionsof preprint data. They also thank R. Shelley,E.G., R. D. Sharp, and R. G. Johnson,Satellite observations of an ionosphericaccelerationmechanism,Geophys.Res. Lett., 3, Vondrak and B. A. Whalen for suggestionsand comments. 654, 1976. The Editor thanks R. Lundin and C. Gurgiolo for their assistance Shelley,E.G., D. A. Simpson,T. C. Sanders,E. Hertzberg, H. Balsiin evaluating this paper. ger, and A. Ghielmetti,The energeticion compositionspectrometer REFERENCES (EICS) for the Dynamics Explorer-A, Space Sci. lnstrum., 5, 443, 1981. Balsiger,H., P. Eberhardt,J. Geiss,and D. T. Young, Magnetic storm injection of 0.9-16keV/e solar and terrestrial ions into the high- Shelley, E.G., W. K. Peterson, A. G Ghielmetti, and J. Geiss, The altitudemagnetosphere, J. Geophys.Res.,85, 1645, 1980. polar ionosphereas a sourceof energeticmagnetosphericplasma, Chappell, C. R., J. L Green, J. F. E. Johnson, and J. H. Waite, Jr., Geophys.Res. Lett., 9, 941, 1982. Pitch-anglevariationsin magnetospheric thermal plasma--Initial Siscoe, G. L., Evidence in the auroal record for secular solar variability, Rev. Geophys.,18, 647, 1980. observationsfrom Dynamics Explorer-l, Geophys.Res. Lett., 9, 933, 1982. Ungstrup, E., D. M. Klumpar, and W. J. Heikkila, Heating of ions to Deehr, C. S., A relation between the altitude of the aurora and solar superthermalenergiesin the topsideionosphereby electrostaticion activity, J. Geophys.Res.,88, 395, 1983. cyclotron waves,J. Geophys.Res.,84, 4289, 1979. Feynman,J., and P. F. Fougere,Eighty-eight-year periodicityin Waite, J. H., Jr., T. Nagai, J. F. E. Johnson,C. R. Chappell, J. L. solar-terrestrialphenomenaconfirmed,J. Geophys.Res., 89, 3023, Burch,T. L. Killeen, P. B. Hays, G. R. Carignan,W. K. Peterson, 1984. and E.G. Shelley,Escapeof suprathermalO + ions in the polar cap, J. Geophys.Res. 90, 1619, 1985. Geiss,J., H. Balsiger,P. Eberhardt, H. P. Walker, L. Weber, D. T. Young,and H. Rosenbauer,Dynamicsof magnetospheric ion com- Whalen, B. A., W. Bernstein,and P. W. Daly, Low altitude acceleration of ionosphericions, Geophys.Res.Lett., 5, 55, 1978. position as observedby the GEOS mass spectrometer,SpaceSci. Rev., 22, 537, 1978. Yau, A. W., B. A. Whalen, A. G. McNamara, P. J. Kellogg, and W. Bernstein, Particle and wave observations of low-altitude ionoGhielmetti, A. G., and R. G. Johnson,Variations in the occurrence sphericion accelerationevents,J. Geophys.Res.,88, 341, 1983. frequencyof UFI eventsfrom July 1976 to April 1979(abstract), Eos Trans. AGU, 64, 807, 1983. Yau, A. W., B. A. Whalen, W. K. Peterson,and E.G. Shelley,Distribution of upflowingionosphericions in the high-altitudepolar cap Ghielmetti,A. G., R. G. Johnson,R. D. Sharp,and E.G. Shelley,The and auroral ionosphere,J. Geophys.Res.,89, 5507, 1984. latitudinal,diurnal,and altitudinaldistributions of upwardflowing energeticions of ionosphericorigin,Geophys.Res.Lett., 5, 59, 1978. Young, D. T., H. Balsiger, and J. Geiss, Correlations of magGorney,D. J., A. Clarke, D. Croley,J. F. Fennell,J. Luhmann,and P. netosphericion compositionwith geomagneticand solar activity,J. Mizera, The distribution of ion beams and conicsbelow 8000 km, Geophys.Res.,87, 9077, 1982. J. Geophys.Res., 86, 83, 1981.
Gurgiolo, C., and J. L. Burch, DE-1 observationsof the polar wind--A heated and unheatedcomponent,Geophys.Res. Lett., 9, 945, 1982.
Harang, L., The Aurorae,Chapman and Hall, London, 1951.
Hultqvist,B., On the originof the hot ionsin the disturbeddayside magnetosphere,Planet. SpaceSci., 31, 173, 1983.
Klumpar, D. M., Transverselyacceleratedions: An ionospheric sourceof hot magnetospheric ions,J. Geophys. Res.,84, 4229, 1979. Klumpar, D. M., W. K. Peterson,E.G. Shelley,Direct evidencefor two-stage(bimodal)accelerationof ionosphericions, J. Geophys. Res., 89, 10,779, 1984.
P. H. Beckwith,PhysicsDepartment,McMaster University,Hamilton, Ont., Canada L85 4M1.
W. K. Peterson and E.G. Shelley, Lockheed Palo Alto Research Laboratory, Palo Alto, CA 94304. A. W. Yau, Herzberg Institute, 100 SussexDrive, Ottawa, Canada K1A 0R6.
(ReceivedDecember 3, 1984; revisedFebruary 25, 1985; acceptedFebruary 27, 1985.)
