Storm track signature in total ozone during northern hemisphere winter

GEOPHYSICAL RESEARCH LETTERS, VOL. 25, NO. t3, PAGES 2413-2416, JULY 1, 1998

Storm track signature in total ozone during northern hemisphere winter Yvan J. Orsolinil, David B. Stephenson and FranciscoJ. Doblas-Reyes M6t•o-France, Centre National de RecherchesM6t•orologiques, Toulouse, France

Abstract. Total ozone has long been known to correlate with tropospheric synoptic eddy activity, with low total ozone associated with anticyclonic conditions. Synoptic eddy activity is particularly intense in the storm track regionsover the North Atlantic and Pacific oceansduring boreal winter. An Eulerian diagnostic was introduced by

Blackmonet al. [1977]to investigatestormtracks,basedon band-passfiltering the 500 mb geopotentialheight for synoptic time scales.Wintertime daily satellite observationsof total ozone have been analyzed using a similar Eulerian approach. Storm track signaturesin total ozone,referredto as ozonetracks,can be discerned.However,the North Atlantic ozone track is stronger than the North Pacific one, and this asymmetry is in part due to intense ozone mini-hole events in the Atlantic sector, causing extreme total ozone variations. During winter 1996/97, this asymmetrywas particularly marked. Furthermore, the Atlantic storm track and the corresponding ozone track were confined to the western Atlantic, due to persistentanticyclonicconditionsover western Europe in late winter and spring. Several intense

tropospheric variability is then dominated by disturbances arising from baroclinic instability of mid-latitude tropospheric westerly jets, which propagate eastwards down-

stream. Blackmonet al. [1977]introduceda widely-used Eulerian measure of storm track activity by defining the Root Mean Square (R.M.S.) deviation of 2.5-6 day bandpassfiltered daily 500 mb geopotential heights. This dispersion measure of storm activity showsclear maxima over the North Pacific and North Atlantic oceans,typically referred

to as stormtracksin the literature [Hoskinset al., 1989]. Total ozone fluctuations have been ascribed to synoptic waves

by using zonal wavenumberdecomposition[Schubertand Munteanu, 1988;Allen and Reck, 1997]. Zonal wavenumber decomposition,however, may not be the most appropriate method for identifying travelling synoptic disturbances,having maximum amplitude in preferred geographicallocations. Only a few studieshave useda time filtering approach. New-

man et al. [1988]used band-passedtotal ozoneto study the longitudinal propagation of Southern Hemisphere mini-

holes.Mote et al. [1991]examinedthe climatologicalsigna-

mini-hole events occurred in the Atlantic sector, with the

ture

strongestevent in mid-March 1997.

ozone, by regressingtotal ozone with band-pass filtered 500 mb geopotential height. ,

of baroclinic

wave trains

in the storm

tracks

on total

In this study, Northern Hemisphere(NH) total ozone

Introduction

fluctuations during winter and spring have been examined Dobsonand Harrison [1926]observedthat fluctuations by band-pass filtering to diagnose the storm track patterns in total ozone over England were correlated with travel- in total ozone, which we refer to as the ozone tracks. We ling weather systems, such as the passageof fronts, with present a 1983-1993 ozone track climatology, and compare low total ozone during anticyclonic conditions. With the it with the ozonetrack in the winter and springof 1996/97. advent of global satellite measurements, many attempts have been made to link zonal asymetries in total ozone in

the extratropicswith planetaryand synopticwaves[Allen Data and Analysis and Reck, 1997; Stephenson and Royer, 1995; Vaughan

and Price, 1988; and referencestherein]. Although the ozone partial pressure peaks near 20-25 km in the mid-

Daily, gridded NH total ozone measurements from the

Total OzoneMappingSpectrometer(TOMS) hasbeenanal-

ysed. The horizontal resolution is 1.25ø in longitude and 1ø in latitude. The climatology is based on 10 years of version tropopause/lower stratosphere regioncan stronglyaffectto- 7.0 TOMS data, from November 1983 to April 1993. During tal ozone through both vertical and meridional ozone ad- the winter 1996/97, the TOMS instrument was aboard the vection[Schoeberland Krueger, 1983]. Exceptionallylow ADEOS satellite, and near-real time data was provided by total ozone values, associatedwith travelling anticyclones NASA Goddard Space Flight Center. Missing data was inare often referred to as ozone mini-holes. terpolated linearly in time between the closest non-missing In this study, we examinein more detail the relationship dates, usually adjacent days. Statistics were compiled for betweentotal ozonefluctuationson synoptictime scales(i.e. extendedwinters (Novemberto April). Daily (12Z) geopolatitude wintertime stratosphere, transient motions in the

lessthan 10 days) during winter and spring,and travelling tential heights were retrieved from the European Centre for extratropical disturbancesin the troposphere. Mid-latitude Medium-RangeWeatherForecasts(ECMWF) globalreanali Now at NorwegianInstitute for Air Research,Kjeller, Norway.

Copyright1998by the AmericanGeophysicalUnion.

yses,at a resolution of 2.8ø Fig. la shows total ozone time series for the 180-day

extended winter 1996/97 at points in the Atlantic storm track (46.5øN, 60øW or point ATL) and Pacific storm track (46.5øN,145øEor point PAC). For comparison,daily

Papernumber98GL01852.

ground-basedtotal ozone observationsare also shown for

0094-8534/98/98GL-01852505.00

the sameperiodat Sapporo,Japan(43øN, 141øE),whichis 2413

2414

ORSOLINI 525

'

'

ET AL.'

i

,

,

STORM

TRACKS

i

i

AND

'

,

TOTAL i

'

OZONE

,

425

325

225 NOV

DEC

525

I

JAN

FEB

i

MAR

[

APR

!

i

425

-

325

225 100

....

i

PAC

,

,

t

,

,

•

,

,

•

,

,

.....

4

o

50. , , I , , I i , I , , I , , I , ,

lOO

•oo..... A-T-L .......... '-...................... i......'......'....... ' .................... '....................... i.......................

lOO

o,.,,.,,,,_, ,v.[Iv,,,., 0

30

60

,

90

v,,,..,

120

150

180

DAYS

Figure 1. (a) Time seriesof daily TOMS total ozonein Dobsonunits for the extendedwinter 1996/97 (November throughApril) overthe PAC and ATL points,and daily ground-based total ozoneat Sapporo,Japan(dottedline). (b) Corresponding TOMS time-series,alsoin DobsonUnits, after 2.5-10day band-passfiltering. Three meanabsolutedeviation limits at the PAC and ATL points are indicated by dotted horizontal lines. at the entrance of the Pacific storm track region. There is

Climatological and 1996/97 Ozone

agreementbetweenthe satellite and ground-baseddata on the amplitude and timing of many synopticfluctuations. Bandpasstime-filtering has been performedat every grid point of the TOMS data usinga 25-pointleast-squares bandpassfilter smoothedin the frequencydomainwith a Dolph-

Tracks Fig. 2a,b showsthe NH climatological M.A.D. of the filtered total ozone and 500 mb geopotential height, calculated

Chebyshev window[DoblasReyesand Deque,1997]. This over 10 winters of data (1983-1993). Elongatedregionsof filter has sharp cut-off frequenciesat 2.5 and 10 days and greatly reducedGibbs oscillations.The filtered time series shown for the ATL and PAC points in Fig. lb retain the synopticvariationsin total ozoneseenin Fig. la. The Mean AbsoluteDeviation (M.A.D.) from the mean is then computed for the 180-dayband-passed time series;the M.A.D. is a more robust statistical estimate of dispersionthan the R.M.$.

deviation.

For a time •cxi•

with a Gaussian distri-

bution, the M.A.D. to R.M.$. ratio is 0.796.

Table

1.

M.A.D.

over the extended

Geopotential height winter

1996/97 averagedover the PAC and ATL sectors, for 7 pressure

levels(in meters). Percentage relative

to

the

300

mb

value

are

given in parenthesis. mb

ATL

enhanced M.A.D. are apparent over the North Atlantic and Pacific.

The ozone M.A.D.

maximizes

at about

20 DU in the

storm track entrance regions,which are also regionsof strong meridional ozone gradient in the lower stratosphere. The ozone track and the storm track stretching toward Europe acrossthe Atlantic oceanmarkedly tilt northward, while the correspondingsignatures over the North Pacific are more zonally orientated. The climatological ozone track over the Pacific is weaker than the Atlantic one. This difference between the Atlantic and Pacific sectors is more noticeable

than in the 500 mb geopotential height storm track, especially if one considersthe spatial extent of the regionof high M.A.D.

This asymmetry is very pronouncedin the extended win-

ter 1996/97 (Fig. 2c,d). A near-zonalring of enhanced ozone M.A.D. is found, with a strong maximum over the Atlantic storm track region, but no clear signature over the North

Pacific.

The

ozone track in the North

Atlantic

re-

semblesthe one seen in the height field. In particular, both PAC

500

55.0(74%)

49.9(76%)

300 200 150 100 70 50

74.2(100%) 65.5(100ø-/o) 60.9(82%) 52.1(80%) 51.2(69%) 43.6(67%) 45.1(61%) 38.4(59%) 42.6(58%) 36.6(56%) 42.1(57%) 36.5(56%)

decayedwell before reachingEurope (see the longitudinal gradient just west of the 30øW meridian), and are hence more confined to the western Atlantic ocean. The poleward

tilt is more marked than in the climatology (Fig. 2), and is associatedwith a long-lasting anticyclonic center over the

westernEurope/Mediterraneanregion. The M.A.D. ozone is broadly reducedover southernEurope, especiallyoverthe Iberian

Peninsula.

ORSOLINI

ET AL.- STORM

TRACKS

AND TOTAL

A

OZONE

GEOP MAD -

õ00

mb

2415

B

ECMWF

,;.. ...... " r'• • ,•J i•.

,

'""

,

'

-.

EX?ENDED

TOMSOZONE(M.A.D.)

EXTENDED

WINTER

C

/ /

WINTER CLFI•[A?OLOGY

D

1996-97

Figure 2. (a) The climatological mean absolutedeviationof band-passfilteredozonetime series,basedon 10 extended wintersof TOMS data, from 1983/84to 1992/93. (b) Samefor the 500mb geopotential height. (c) Mean absolutedeviation of band-pass filteredtime seriesfor the extendedwinter 1996/97 for ozoneusingTOMS ADEOS data. (d) Samefor 500 mb geopotentialheight. Units for DobsonUnits (a,c) and meters (b,d). Latitude circlesare at 30øN and 60øN.

Ozone Mini-holes Between

and the Asymmetry

the Atlantic

and Pacific

Ozone

Tracks There is a pronouncedasymmetry between the Atlantic and Pacific ozone tracks. Previous analysesof TOMS data have also noted less high zonal-wavenumber variance over

baroclinic waves obtained from linear regressionof geopotential heights is the same in both the Pacific and Atlantic sectors. Table I showsthe geopotential M.A.D. averaged

from 40øN to 60øN, over a 60ø longitudesectorcoveringthe Atlantic and Pacific storm tracks at sevenpressurelevelsfor the extendedwinter 1996/97. The M.A.D. decaysvertically

at the same rate over the two regions above a maximum located near the tropopause. the North Pacificthan over the North Atlantic [Schubert Careful inspection of Figs. la,b shows the occurrence and Munteanu, 1988;Allen and Reck, 1997],but no explaof several extreme eventsover the ATL point during which nation has been proposed. The Atlantic storm track diagtotal ozone diminishes rapidly. Total ozone filtered fluctuanosed in the 500 mb height field, on the other hand, is only tions higher than 3 M.A.D.s occurred near January 10-15, slightly larger than the Pacific one. Although, the winterFebruary 15, and especially March 15. The ATL time series time jet over the North Pacific is climatologically stronger, the baroclinic eddy activity in the Pacific storm track dis- hasa M.A.D. of 21.9, and a R.M.$. deviation of 28.61, giving plays more intraseasonal variability, such as a recurrent de- a ratio of 0.765, and the kurtosis is 3.7; the M.A.D to R.M.$. clinein midwinter[Nakamura,1992]. Fig. lb showsindeed ratio inferior to 0.796, and the kurtosislarger than 3 indicate non-Gaussianstatistics, and a distribution with longer tails lesspronouncedozone fluctuations in January over the PAC than Gaussian. For the PAC time series,the corresponding point. Differences in the synoptic eddy vertical structure can be values are 17.18, 21.66, 0.793 and 2.8, in closer agreement ruled out as a source of this discrepancy in ozone signature. with Gaussian behavior. Hence, the ATL time series has Lim [1989]showedthat the characteristic verticalscaleof the larger dispersionthan the PAC time series,mainly because

2416

ORSOLINI

ET AL.: STORM

TRACKS

of the few extreme events. Other fluctuations apart from these few events are nearly of the same amplitude over both ATL and PAC points. The largestdeviationsover ATL occur when total ozonedecreasessignificantly,and we refer to these events as ozone mini-holes, without defining a precise threshold.

The ozone mini-holes

over the North

Atlantic

could account for the enhanced Atlantic ozone track, e.g.

in 1996/97. Large-amplitudemini-holes,characterised by a decreaseof 70 DU or more from the monthly mean to-

tal ozoneare more prominentoverthe North Atlantic than over the North Pacific, and appear predominantly in Febru-

ary. Particularlyintensemini-holesare associated with large

polewardexcursion of low-latitude,ozone-poor air [McCormackand Hood, 1997;Orsoliniet al., 1995].The persistent blocking over western Europe noted above in late winter and springin 1997 favouredstrongnorthwardexcursionsof low-latitude air to the west of the standing high anomaly.

A likely explanationfor the mini-holespreferredoccurrence in the Atlantic sector is that the stronger subtropical

jet over the Pacific prohibits large meridionalexcursionsof subtropicalair. Over the Atlantic sectorhowever,the subtropical jet is weaker and large amplitude advectionof subtropical, ozone-poorair can occur more frequently. Ozone meridional advection could also be reinforced when the po-

lar vortexis displacedtowardEurope[Orsoliniet al., 1995]. The existence of extreme ozone events in the Atlantic sector

could have impact on ozonedata assimilation. Acknowledgments. The NASA GSFC is gratefully acknowledgedfor providing the TOMS data. Ground-basedozone measurements were made available at the World Ozone Data Cen-

tre (Toronto) by the Japan MeteorologicalAgency.

References Allen, D.R., and R.A. Reck, Daily variations in TOMS total ozone data, J. Geophys. Res., 102, 13603-13608, 1997. Blackmon, M.L., et al., An observationalstudy of the Northern Hemisphere wintertime circulation, J. Arm. Sci., 34, 1040-

AND TOTAL

OZONE

Dobson, G.M.B., and D.N. Harrison, Measurements of the amount of ozone in the earth's atmosphere and its relation to other geophysicalconditions: Part I, Proc. R. Soc. London, A 110, 660-693, 1926.

Hoskins, B.J., et al., Diagnostics of the global atmospheric circulation based on ECMWF analyses 1979-1989, World Climate

ProgrammeResearch,WMO/TD-

326, 1989.

Lim, G.H., The observed three dimensional structure of baroclinic waves in the northern hemisphere winter as revealed in a linear regressionanalysis, Ph.D. thesis, Dept. of Atmospheric Sciences,University of Washington, Seattle, 1989. McCormack J.P., and L.L. Hood, The frequency and size of ozone "mini-hole" eventsat northern midlatitudes in February, Geophys. Res. Lett., œ4,2647-2650, 1997. Mote, P.W., J.R. Holton and J.M. Wallace, Variability in total ozone associatedwith baroclinic waves, J. Arm. Sci., 48, 19001903, 1991.

Nakamura, H., Midwinter suppressionof baroclinic wave activity in the Pacific, J. Arm. Sci., 48, 1900-1903, 1992. Newman, P.A., L.R. Lait and M.R Schoeberl, The morphology and meteorology of southern hemisphere spring total ozone mini-holes, Geophys. Res. Left., 15, 923-926, 1988. Orsolini, Y.J., D. Cariolle, and M. Deque, Ridge formation in the lower stratosphere and its influence on ozone transport: a GCM study during late January 1992, J. of Geophys. Res., 100, 11113-11135, 1995. Schoeberl,M.R., and A.J. Krueger, Medium scaledisturbancesin total ozone during southern hemisphere summer, Bull. Amer. Met. Soc., 64, 1358-1365, 1983. Schubert, S.D., and M-J. Munteanu, An analysis of tropopause pressure and total ozone correlations, Mon. l/Vea. Rev., 116, 569-582, 1988.

Stephenson,D.B., and J-F. Royer, Low-frequency variability of TOMS and GCM total ozone stationary waves associatedwith the E1 Nino/Southern Oscillationfor the period 1979-88, J. of Oeophys. Res., 100, 7337-7346,1995. Vaughan, G., and J.D. Price, On the relationship between total ozone and meteorology, Quart. J. Royal Met. Soc. , 117, 1281-1298, 1991.

F.J. Doblas-Reyes, Y.J. Orsolini and D.B. Stephenson, M•t•oFrance CNRM, 42 avenue G. Coriolis, 31057 Toulouse Cedex,

France. (email: [email protected])

1053, 1977.

Doblas-Reyes,F.J., M. and Deque, A flexible bandpassfiltering procedureapplied to midlatitude intraseasonalvariability, Mon.

Wea. Rev., in press, 1998.

(Received March3, 1998; acceptedMay 8, 1998.)