中性风对夜侧电离层纬向四峰结构的影响.pdf
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1、XiongC,RangXY,HuangYY,JiangGY,HuK,LuoWH.2024.Latitudinalfour-peakstructureofthenighttimeFregionionosphere:Possiblecon-tributionoftheneutralwind.ReviewsofGeophysicsandPlanetaryPhysics,55(1):94-108.doi:10.19975/j.dqyxx.2023-009.Latitudinal four-peak structure of the nighttime F region ionosphere:Possi
2、ble contribution of the neutral windXiongChao1,2*,RangXinyi2,HuangYuyang2,JiangGuoying3,HuKun2,LuoWeihua41HubeiLuojiaLaboratory,Wuhan430079,China2DepartmentofSpacePhysics,ElectronicInformationSchool,WuhanUniversity,Wuhan430072,China3StateKeyLaboratoryofSpaceWeather,NationalSpaceScienceCenter,Chinese
3、AcademyofSciences,Beijing100084,China4CollegeofElectronicInformationandEngineer,South-CentralUniversityforNationalities,Wuhan430074,ChinaAbstract:Inthisstudy,weprovideadetailedanalysisofthelatitudinalfour-peakstructureoftheFregionelectrondensityobservedbytheSwarmBsatelliteduringthenightofJanuary31,2
4、017.Consistingofthreesatel-litesflyingatdifferentlocaltimes,Swarmprovidesanopportunitytoinvestigatethetemporalevolutionofthenighttimelatitudinalfour-peakstructure.Forthisevent,SwarmA/Cdidnotobservethetwocrestsofequatorialionizationanomaly(EIA)at17:55/18:01LT,butSwarmB,whichflewoverthesamelongitudina
5、lsectorapproxi-mately4.5hlater,observedaclearlatitudinalfour-peakstructure.Thisprovidesdirectevidencethatthetwoinnerpeaksofthelatitudinalfour-peakstructurearenotremnantsoftheEIAcrestsfromsunset.Inaddition,simultan-eousmeasurementsoftheverticalplasmadriftfromtheincoherentscatterradaratJicamarcaandneu
6、tralwindfromtheground-basedFabryPerotinterferometer(FPI)atArecibowerecomparedtorevealthepossibledrivingmech-anisms.TheobservedFregionverticalplasmadriftwasgenerallydownwardfromsunsetthroughoutthelocalnightofJanuary31,2017,whichrevealsthatanenhancedupwardplasmadriftisnotnecessarytocausethenighttimela
7、ti-tudinalfour-peakstructure.TheneutralwindmeasurementsfromtheFPIlocatedatAreciboshowedenhancedeast-wardandsouthwardcomponentsduringthenightwhenthelatitudinalfour-peakstructurewasobservedbySwarmB,bothwithadifferenceofapproximately100m/scomparedwiththeothertwodays.Thissuggeststhattheneu-tralwindsplay
8、animportantroleinthenighttimelatitudinalfour-peakstructure.FurthersimulationsusingtheSAMI2(anothermodeloftheionosphere)modelsupporttheseobservations.Ingeneral,eastwardandequatorwardwinds from both hemispheres at night provided favorable conditions for the latitudinal four-peak structure.However,when
9、theequatorwardwindistoolarge,astronghemisphericasymmetryofthebackgroundNecanoc-cur,whichpreventsthedevelopmentofthelatitudinalfour-peakstructureatnight.Keywords:nighttimeionosphere;equatorialionizationanomaly;latitudinalfour-peakstructure;Swarmsatel-lites;neutralwind0IntroductionA well-known phenome
10、non in the low-latitudeionosphericFregionduringdaytimeistheequatorialionizationanomaly(EIA),whichischaracterizedbyanelectrondensity(Ne)troughabovethemagneticequa-toranddoublecrestsofenhancedNeatapproximately15 north and south of the magnetic equator(e.g.,Appleton,1946;Liang,1947;Namba and Maeda,Rece
11、ivedFebruary26,2023;AcceptedMay17,2023ThisresearchwassupportedbytheSpecialFundoftheHubeiLuojiaLaboratory(GrantNo.220100011),andtheNationalKeyR&DProgramofChina(GrantNo.2022YFF0503700).XiongChaoissupportedbytheDragon-5Cooperation2020-2024(ProjectNo.59236),andtheInternationalSpaceScienceInstitute(ISSI)
12、inBernandBeijingthroughISSIInternationalTeamProject#511(Multi-ScaleMagnetosphere-Ionosphere-ThermosphereInteraction).*Corresponding author.XiongC,email:第55卷第1期地球与行星物理论评(中英文)Vol.55No.12024年1月ReviewsofGeophysicsandPlanetaryPhysicsJan.,20241939).The daytime EIA is driven by the equatorialplasma fountai
13、n effect.In the equatorial region,themagneticfieldlinesareprimarilyhorizontal,pointingnorthward,and the daytime eastward electric fielddrives the plasma upward via EB drift.Owing togravitationalandpressure-gradientforces,theup-liftedplasma diffuses poleward and sediments downwardalongthe geomagnetic
14、 field lines into both hemi-spheres,formingtwodensitycrestsalongsidethemag-neticequator(Duncan,1960).ThetwoEIAcreststypi-cally appear at approximately 09:00 local time(LT)andmovepolewardataspeedofapproximately1oflatitudeperhourforthenextfewhours(Yehetal.,2001).TheEIAintensity,representedbythecrest-t
15、o-trough ratio(CTR)of the EIA,gradually increasesfrommorningtonoon,thenslightlydecreasesintheafternoon,and finally reaches its maximum valuebetween18:00and20:00LT;thismaximumisalmosttwicethedaytimelevel(e.g.,Liuetal.,2007;Xiongetal.,2013).TherapidlyincreasingCTRvalueaftersun-setisprimarilyrelatedtot
16、heprereversalenhancement(PRE),whichisdefinedasasharpincreaseinplasmaverticaldriftaftersunsetviaenhancementoftheeast-wardelectricfieldintheionosphericFregion.TheFregiondynamo,drivenbytheFregionneutralwindincombinationwiththeconductivitycontrastacrosstheday-night terminator,is accepted to cause the PR
17、E(e.g.,Ecclesetal.,2015;Kelley,2009).PreviousstudiesrelatedtotheEIAhavefocusedmainly on its morphology during the daytime andshortlyaftersunset,whileitsappearanceandrelatedmechanism around midnight have not been welladdressed.Woodman(1970)usedradarobservationstoreportthepost-midnightEIAfeaturesdurin
18、gmag-netically disturbed periods.Wang et al.(2008)sug-gested that disturbed electric fields during storm orsubstorm periods can produce upward plasma drift,formingtheEIAduringlate-nighthours.Inaddition,McDonaldetal.(2008)foundthatduringgeomagneti-cally quiet periods,the enhanced EIA during PREhours
19、can sometimes last until post-midnight hours.However,Yizengawetal.(2009)arguedthatthetwopeaksoftheEIAduringpost-midnighthoursinquietperiods are not the remains of the EIA from sunsethours;instead,they are caused by reversed verticalupwarddriftsrelatedtotheFregionwinddynamodur-ingpost-midnighthours.T
20、herefore,thegenerationofthepost-midnightEIA,especiallyduringmagneticallyquietperiods,remainsanopenissue.Usingoccultation measurements from the Con-stellationObserving System for Meteorology,Iono-sphere,andClimate(COSMIC)satellites,Zhongetal.(2019)showedthatthenighttimeelectrondensitiesat40 magnetic
21、latitude(Mlat)are generally greaterduringequinoxes,formingtwobandsatalllongitudes;duringsolsticesthemiddlelatitudebandinthewinterhemisphereismuchmoreprominent.ThisnighttimeionosphericbandstructureatmiddlelatitudesshouldrepresentthesamephenomenaaspreviouslyreportedfornighttimeenhancementsoftheF2elect
22、rondensitypeak,NmF2(e.g.,Arendt and Soicher,1964;Balanand Rao,1987;Jakowski and Frster,1995).Theseenhancementsarealsomoreoftenobservedinthewin-terhemisphereandaresuggestedtobecausedbytheenhancedequatorward meridional wind and down-ward diffusion from the plasmasphere at night(Mikhailovetal.,2000;Zho
23、ngetal.,2019).Comparedtoground-basedandCOSMICobser-vations,insituNemeasurementsfromlowEarthorbit-ing(LEO)satellitesflyinginnear-circularandpolarorbits,e.g.,the Swarm satellites,provide a goodopportunitytoinvestigatethelatitudinaldistributionoftheionosphere.With an orbital velocity of approxi-mately
24、7.5 km/s,the Swarm satellites travel alongalmostthesamemagneticmeridian,withlessthan30minfromonehemispheretotheotheratlowandmid-dlelatitudes.Withinsuchaperiod,large-scaleiono-sphericstructuressuchastheEIAarenotexpectedtochangesignificantly.Xiongetal.(2019)reportedthatthe two Ne peaks at low latitude
25、s could still beobservedbySwarmduringpost-midnighthours,andtwoadditionalpeaksweresometimesalsoobservedatnorthernandsouthernmiddlelatitudes,formingalati-tudinalfour-peakstructureinthenightsideionosphere.Onaverage,suchlatitudinalfour-peakstructureshaveverylowoccurrencerates,accountingforonly4%of第55卷第1
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