Decreasewinds演唱会

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doi:10,1016/SO273-1177(03)00678-lSOLARACTIVITYDEPENDENCEOFEFFECTIVEWINDSDERIVEDFROMIONOSPHERICDATAATWUHANLiboLiu,WeixingWan,XiaoliLuan,BaiqiNing,andJiuhouLeiWuhanIonosphericObservatory,WuhanInstituteofPhysicsandMathematics,ChineseAcademyofSciences,Wuhan,430071,ChinaABSTRACTThesolarcyclevariabilityofthermosphericcirculationisoneoftheoutstandingquestionsinvolvingtheupperatmosphere.
However,itneedstobeidentifiedduetothelatitudeandlongitudedependenceofneutralwinds.
Thisarticleexaminesthesolaractivitytrendsintheverticalcomponentofequivalentwinds(VEWs)derivedfromionosondedataduring1966-1985overWuhan(114.
4'E,30.
6'N,45.
2"dip)ofChina.
ThemonthlymediandataofroutineionosondemeasurementsinpublishedtablesareusedtoderiveVEWswhicharecontributionsfrombothneutralwindsandzonalelectricfields.
ThesolaractivitytrendsofVEWsoverWuhanhaveanobviouslocaltimeandseasonaldependence.
OverWuhan,themagnitudesofVEWsdecreasewithincreasingsolaractivityaroundmidnightforallseasonsandaroundmiddayinwinterandautumn.
Incontrast,littlevariationisfoundthroughoutthesolarcyclearoundmiddayinsummerandspring.
ThemagnitudesofdailymeansandamplitudesofdiurnalandsemidiurnalcomponentsofVEWsoverWuhandecreasewithsolaractivity,whichalsoconfirmsthatitisnotafeatureofaparticularlocation.
ThereisamorepronounceddecreaseindiurnalamplitudesofVEWsthanotherharmoniccomponentsoverWuhan.
Thedecreaseindiurnalamplitudeswithincreasingsolaractivitycanbereasonablyexplained,ifthegreateriondragatsolarmaximumcompensatesforpressuregradientsduetothegreaterEWinput.
02003COSPAR.
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INTRODUCTIONUnderstandingthevariationofthermosphericcirculationsisanimportantsubjectinvolvingthecouplingsystemoftheupperatmosphereandionosphere.
Thesolarcyclevariabilityofthermosphericcirculationshasbeenstudiedwithmeasurementsandtheoreticalandempiricalmodeltechniquesforyears.
Currentmodelsandmeasurementsshowthat,althoughneutralcompositionsandtemperatureinthethermosphereclearlyandstronglydependonthelevelofsolaractivity,thesolaractivityvariationsofthermosphericmeridionalwindsarecomplexanddifferentatparticularsites(Hedinetal.
,1994).
Itisreportedthat,withincreasingsolaractivity,thediurnalamplitudesofmeridionalwindsdecreaseatsomelocations.
Butoppositetrendsarefoundinsomeseasonsandsomelocations(e.
g.
,DuboinandLafeuille,1992;Aruliahetal.
,1991,1996;Arriagadaetal.
,1997).
Atahigh-latitudesite,Kiruna(67.
8'N,20.
4"E)ofSweden,ahighersolarfluxresultsinthemagnitudeoftheFPImeridionalwindsbeinglargerforeachseason(Aruliahetal.
,1991,1996).
Hedinetal.
(1994)foundthewindsatAdv.
SpaceRes.
Vol.
32,No.
9,pp.
1719-1724.
200302003COSPAR.
PublishedbyElsevierLtd.
AllrightsreservedPrintedinGreatBritain0273-l177/$30.
00+0.
001720L.
Liuetal.
mid-latitudeshavenocleardependenceonthesolaractivitylevel.
ThemeridionalneutralwindsfromtheEISCATradarshowanF107dependence:themeanwindsarelargerduringlowsolaractivityperiods,whilethetrendsareoppositeinthesemidiurnalcomponents(Witasseetal.
,1998).
Decreaseindiurnalamplitudesofthederivedwindswithsolaractivitylevelsisfoundatamid-latitudestation,Boulder(40.
0°N,254.
7'E)(Buonsanto,1991).
Whileatanothermid-latitudestationinthesouthernhemisphere,KingGeorgeIsland(62.
2'S,58.
8"W),theamplitudesofwindsdecreasefromlowtohighsolaractivitylevelsinspringandsummer,butincreaseinwinter(Arriagadaetal.
,1997).
Thusthedetailsofthesolarcycleand/orseasonalanalysesdifferfromstudytostudy(Hagan,1993)andfromlocationtolocation.
Untilnow,therearefewinvestigationsonthesolaractivitytrendofwindsinChina,andthepatternisnotclearyet.
Thusitneedstobeidentifiedduetothelatitudeandlongitudedependenceofneutralwinds.
Thisarticleinvestigatesthesolaractivityleveltrendsofverticalequivalentwindsdeducedfrommonthlymedianionosphericdataduring1966-1985overWuhan(114.
4'E,30.
6"N,dip45.
2'),China.
DATAANDMETHODOFANALYSISTheionosphereaboveWuhanhasbeenroutinelymeasuredforalongtime.
Inthiswork,themonthlymedianionosphericdatainpublishedtablesduring1966-1985isutilizedtoderivetheverticalcomponentofequivalentwinds(VEWs)aroundthepeakofF-layeroverWuhari.
Basedonthesensitivityofmagneticmeridionalwinds,theheightandcriticalfrequencyoftheFpeakcanbeusedtoestimatetheverticalcomponentofequivalentwindsalongthemagneticmeridianthroughoutdayandnight(Hedinetal.
,1994;Titheridge,1995).
Unfortunately,therearenoelectricfieldmeasurementsoverWuhan.
Toavoidintroducingfalseinformation,wedonotestimatetruewindswithacorrectionofelectricfieldsbutconductinvestigationonVEWsdirectly.
TheDudeney(1983)methodisusedforestimatinghmF2fromthemonthlymedianfoF2,M3000F2andfoE.
TheVEWsarededucedfromionosphericdatawiththemethodofLiuetal.
(2003a,2003b)andLuanetal.
(2002).
Theeffectivewindsarefoundtobewellagreeablewithactualmeasurements(e.
g.
FPI,MillstoneHillIncoherentScatterradardata)andtheservomethod.
TheneutralparametersareprovidedfromtheMSISmodel.
Thewindsareoftenrepresentedbyonemeanandthreeharmoniccomponentswithperiodsof24,12,and8hours,whichalsobecalleddiurnal,semi-andter-diurnalcomponents.
Aleast-squareharmonicanalysishasbeenperformedthederivedVEWsoverWuhanforeachmonthduring1966-1985usingthefollowingequation(e.
g.
DuboinandLafeuille,1992;Witasseetal.
,1998):w(t)=w,+4,COS[Q(t-tz4)]+A,zcos[w12(t-t,*)]+A,cos[o,(t-f8)]+C(e),wherew,=2r/n,n=24,12,8,e(e)isthecorrespondingerrorterm.
RESULTSOverWuhanthederivedVEWshavedistinctlocaltimeandseasonalvariations.
Ingeneral,theVEWsarelargerdownwardduringthedaytimeandsmallerupwardatsomeintervalsinthenighttime.
ThelocaltimepatternsareverysimilarwiththoseofhmF2.
ToinvestigatethesolarcycletrendofVEWsforseasons,thededucedVEWdatafor1966-1985aresortedintoseasonasfollows:summermonthsarefromMaytoAugust;wintermonthsareNovember,December,JanuaryandFebruary;springmonthsareMarchandApril;andautumnmonthsareSeptemberandOctober(Buonsanto,1991).
Toobtainmoredetailedinformationoftheirtrends,thedataareshownoverthef&lrangeofsolaractivityandnotsortedintotwosolaractivitylevels(solarminimumandmaximum).
Thisisdifferentfrompreviousstudies.
AninterestingandsignificantfeatureisthatthesolarcycletrendofVEWsoverWuhandependsonlocaltime.
SolarActivityDependenceofEffectiveWindsatWuhan1721Figure1illustratesthesolarcycletrendandcorrelationcoefficients(r)ofVEWsaroundmidday(localtime1l-13h)andmidnight(localtime23-1h)forfourseasonsduringtheperiodof1966-1985overWuhan.
Positivevaluescorrespondtoupwardverticalvelocities,orsouthwardneutralwinds.
AroundmidnightoverWuhan,themagnitudesofVEWstendtodecreasewithincreasingsolaractivityforfourseasons.
Thetrendwithsolaractivityisobviousaroundmidnightforallseasonsandmoresignificantisfoundinsummerandspring.
Withhighersolaractivity,themagnitudesofVEWsdecreasearoundmiddayinwinterandautumn.
Incontrast,littlechangethroughoutthesolarcycleisfoundaroundmiddayinsummerandspring(ronly-0.
16and-0.
12).
ThesolaractivitytrendsofVEWsaremostdistinctinwinteraroundbothmiddayandmidnight(Figure1).
AharmonicanalysisofVEWsisperformedasafunctionoflocaltimeforeachmonth.
Figures2-4showthedailymeansandamplitudesofthreeharmoniccomponentsofVEWsoverWuhanwithperiodsof24,12and8hasafunctionofsolaractivityforseasons.
Theharmonicresultsshowsomefeaturesofthesolaractivityvariability.
TheseasonalbehaviorofVEWsoverWuhanandhowitisinfluencedbythelevelsofsolarfluxcanbeinvestigatedwiththedailymeanvaluesdepictedinFigure2.
ThedailymeanVEWsaredownwardforallseasonsexceptinsummer(r=0.
03).
ThedownwardmeanVEWsarelargerinautumnthaninspring.
ThemagnitudesofdailymeanVEWsdecreasewithincreasingsolaractivityexceptinsummer.
ThedecreaseinmagnitudesofmeanVEWsisfoundmostobviousinautumn,muchsmallerinspring,andlittlesolaractivityvariationisfoundinsummer.
AnobviousreductionindiurnalamplitudesofVEWswithincreasingsolaractivityisfoundduringallseasons.
Thesolaractivityvariationofdiurnalamplitudesinwinterismoresignificantthanthoseinotherseasons.
Andthesolardependenceofdiurnalamplitudeinspringissmallerthaninotherseasons.
Incontrast,thesolarcyclevariationofthediurnalamplitudesinsummerissmallerthanthatinotherseasonsatBoulder(Buonsonto,1991).
ItisinterestingtonotefromFigure4thatthesemi-andter-diurnalamplitudesofVEWsalsodecreasewithincreasingsolaractivityforallseasonsexceptinwinter.
Littlechangeinsemidiurnalamplitudesisfoundinwinter.
DISCUSSIONANDSUMMARYThewindbehaviorasafunctionofsolarfluxisnotyettobeunderstoodcomprehensively.
InthisarticleVEWsderivedfromionosondemeasurementsduring1966-1985overWuhanareanalyzedtoinvestigatetheinfluenceofsolarfluxes.
SolarcyclevariabilityofVEWsfromChineseionosphericdataforsuchalongperiodisreportedforthefirsttime.
AlthoughVEWscanbededucedonlyatthepeakofFlayer,duetoveryhighviscosityataltitudesabove200km,thereshouldbesmallheightvariationofthermosphericwindsabovethatheight.
ThustheVEWsderivedatthepeakoftheionosphericF-layerwhichvarieswithsolaractivityshouldnothaveseriousinfluencesontheconclusionoftheinvestigationpresentedabove.
Asdescribedabove,therearelargelocaltimeandseasonalvariationsandrelativelysmallersolarcycledependenceintheVEWsderivedfromionosphericdataatWuhan.
ThesolaractivitytrendsofVEWsoverWuhanhaveobviouslocaltimeandseasonaldependence.
ThemagnitudesofVEWsdecreaseswithincreasingofsolaractivityaroundmidnightforallseasonsandaroundthemiddayinwinterandautumn.
Incontrast,itisnotobviousaroundmiddayinsummerandspring.
OverMillstoneHill,themagnitudesofthenighttimewindsduringsolarmaximumarealsoremarkablysmallerthanthoseofsolarminimumnighttimewinds,butthedaytimetrendisopposite(Hagan,1993).
ThereforetherearedifferenttrendsbetweendaytimewindsatWuhanandMillstoneHill.
ThedailymeanandamplitudesoftidalcomponentsofVEWsdecreasewiththeincreasingsolaractivity.
ThepresentworkshowsthattherearemorepronouncedsolartrendsofdiurnalamplitudesofVEWsthanotherharmoniccomponentsoverWuhan.
Incontrast,thesolarcyclevariabilityintheMillstoneHilldailymeanwindsismorepronounced(Hagan,1993).
AndtheseasonaldependenceofsolarcyclevariationofthediurnalamplitudeoverWuhanisalsodifferentfromthatatBoulder(Buonsanto,1991).
Consistencyisfoundbetweenthepresentresultsandpreviouslyfoundtrendsofdecreasingamplitudeofthediurnalvariationwithincreasingsolaractivitylevel.
Thisworkconfirmsthattheabovetrendisnotafeatureofaparticularlocation(Hedinetal.
,1994).
1722L.
Liuetal.
Midday340z309-40';;'40B30P-40Q40k303-4040g;O5-40Midnightr=-0.
56r=-0.
55.
:$++&-$Q.
r=-0.
65r=-0.
47!
r=0.
61WinterSummerr=-0.
16.
Springr=-0.
12r=0.
45Autumn-40g9-80402B03s-40403B035;;bo100150200100150200F107F107Fig.
1.
MiddayandmidnightVEWs(upwardpositive)versusF107forseasonsduring1966-1985overWuhan.
Thecorrelationcoefficient,r,isalsoshownineachpanel.
Theindividualpointsrepresentthevaluesforeachmonth.
0-105-203"-30-40-500.
.
.
l*l*.
*.
.
-10l-t*.
ys.
*.
r.
-0'z.
:.
*i;.
.
l-0.
'.
-.
9.
.
.
.
.
Winterl10.
'.
*S&er.
--20r,=0.
37l'ro=0.
03103-10.
'l**'l.
--3lgt-.
-20:bl.
.
3O-30.
.
-30.
Spring:'Al&13"-40ro=0.
20ro=0.
45-40-50100150200100150200-50F107F107Fig.
2.
DailymeanofVEWsversusF107forseasonsduring1966-1985.
Solidlineshowsthelinearfittingtrend.
r.
labeledineachpanelaretherelatedcorrelationcoefficients.
SolarActivityDependenceofEffectiveWindsatWuhan1723r34=-0.
89Itr,A=-0.
63Autumn'0F107F107Fig.
3.
SameasFig.
2butfortheamplitudesofdiurnal(24h)component.
ig308z20-p10cd0g30g220210(d0Summer-.
-Spring-lr-Al.
ltUrrmJ,1100150200100150200F107F107jli30201003020100Fig.
4.
SameasFig.
2butforthesemidiurnal(dotpoints)andterdiurnal(plussymbols)components.
Heavyandthinlinesarethelinearfitforsemidiurnalandterdiurnalcomponents,respectively.
r12andrsarecorrelationcoefficients.
Thethermosphericwindisprimarilydrivenbypressuregradientsgeneratedbythesolarradiations(mostlyintheequatorialregionsduringthedaytime)andaurora1heating(inauroraregions)(Titheridge,1995).
ThemotionoftheatmosphereisretardedmainlybyiondragsandCoriolisforces.
Althougheachissolarcycledependent,theeffectsofsolarheatingandiondragappeartocanceleachotherout.
Thefactorswhetherinroughbalanceornotdeterminethewindswithlittleorsignificantsolaractivity.
Theabsenceofanobvioussolarcyclevariationisexplainedbythecompetingeffectsofincreasedenergyinputandiondragatsolarmaximum.
Whilewiththedecreaseinsolaractivityitisreasonabletothinkthatthewindwillbelesspolewardasaresultofrelativelysmaller1724L.
Liuetal.
effectofpressuregradients(Witasseetal.
,1998).
Incontrast,increasediondragduringsolarmaximummayplayanimportantroleintheinterpretationofthedecreaseindiurnalamplitudeofwindswithincreasedsolaractivity.
IondragisstrongestduringdaytimewhenFregiondensitiesarehigher;thusthewindsareslowerduringthedayincomparisontonighttime.
Withtheenhancementofsolaractivity,iftheiondragincreasessogreaternotonlytocompensateforthegreaterpressuregradients,thediurnalamplitudewilldecrease.
Theoutstandinglimitationsinvolvingthisinvestigationareasfollows:(1)TheinvestigationisconductedontheVEWsratherthanthetruewindsbecauseestimatedelectricfieldsarenotsubtractedtoestimatethetruewinds.
(2)Geomagneticactivitiesmayhavesignificanteffectsonwinds.
InthepresentstudytheVEWsarederivedfromthemonthlymedianvaluesofionosphericdatawhichmaypartlyincludetheinfluenceofgeomagneticdisturbances.
HowmuchthegeomagneticstormsincludedmaydistorttheresultsoverWuhanneedsfurtherstudies.
ACKNOWLEDGMENTSThisresearchissupportedbyNaturalScienceFoundationofChina(40274054,40134020)andNationalImportantBasicResearchProject(G2000078407).
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E-mailaddressofLiboLiulliu@winm.
ac.
cnManuscriptreceived19October2002;revised31March2003;accepted29April2003