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SpacePhysicsandAeronomyCollectionVolume2 GeophysicalMonograph259

MagnetospheresintheSolarSystem

RomainMaggiolo

NicolasAndré HiroshiHasegawa

DanielT.Welling

Editors

YongliangZhang

LarryJ.Paxton CollectionEditorsinChief

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Names:Maggiolo,Romain,editor.|André,Nicolas,1977– editor.| Hasegawa,Hiroshi,1974– editor.|Welling,DanielT.,editor.

Title:Magnetospheresinthesolarsystem/RomainMaggiolo,Nicolas André,HiroshiHasegawa,DanielT.Welling,editors.

Description:Hoboken,NJ:Wiley-AmericanGeophysicalUnion,[2021]| Includesbibliographicalreferencesandindex.

Identifiers:LCCN2020045732|ISBN9781119507529(cloth)|ISBN9781119829980(adobepdf)|ISBN 9781119815648(epub)

Subjects:LCSH:Magnetosphere.|Planets–Magnetospheres.

Classification:LCCQC809.M35M322021|DDC538/.766–dc23

LCrecordavailableathttps://lccn.loc.gov/2020045732

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Setin10/12ptTimesNewRomanbySPiGlobal,Pondicherry,India

10987654321

CONTENTS

ListofContributors ..................................................................................................................................................ix

Preface ...................................................................................................................................................................xvi

PartI:TheEarthMagnetosphere ...............................................................................................................................1

1ABriefHistoryoftheMagnetosphere ..............................................................................................................3 DavidJ.Southwood

2Large-ScaleStructureandDynamicsoftheMagnetosphere .........................................................................15 DavidG.SibeckandKyleR.Murphy

3TheEquationsoftheMagnetosphere .............................................................................................................37 HerbertGunell

PartII:FundamentalProcesses ...............................................................................................................................47

4MagneticReconnectionintheNear-EarthMagnetotail .................................................................................49 TsugunobuNagai

5TurbulenceandComplexityofMagnetosphericPlasmas...............................................................................67 MariusEchim,TomChang,PeterKovacs,AnnaWawrzaszek,EmiliyaYordanova,YasuhitoNarita, ZoltanVörös,RobertoBruno,WieslawMacek,KaleviMursula,andGiuseppeConsolini

6Wave–ParticleInteractionsintheEarth’sMagnetosphere ............................................................................93 RichardM.Thorne,JacobBortnik,WenLi,andQianliMa

7Cross-ScaleEnergyTransportinSpacePlasmas:ApplicationstotheMagnetopauseBoundary .................109 KatariinaNykyri,XuanyeMa,andJayJohnson

PartIII:SolarWind–MagnetosphereCoupling .....................................................................................................123

8SolarWindInteractionwithEarth’sBowShock ..........................................................................................125 Georges.K.Parks,EnsangLee,ZhongweiW.Yang,NaiguoLin,SuiyanY.Fu,andYingLiu

9TheMagnetosheath ......................................................................................................................................137 YasuhitoNarita,FerdinandPlaschke,andZoltánVörös

10DaysideMagnetopauseProcesses ................................................................................................................153 StephenA.Fuselier

11ThePolarCuspsoftheEarth’sMagnetosphere ............................................................................................163 BenoitLavraudandKarlheinzJ.Trattner

12TheEarth’sLow-LatitudeBoundaryLayer ....................................................................................................177 TakumaK.M.Nakamura

viCONTENTS

PartIV:Magnetosphere–IonosphereCoupling .....................................................................................................193

13Field-AlignedCurrentsintheMagnetosphere–Ionosphere ..........................................................................195 HermannLührandGuramKervalishvili

14IonosphericIonAccelerationandTransport ................................................................................................207 AndrewW.Yau,TakumiAbe,MatsAndré,AndrewD.Howarth,andWilliamK.Peterson

15ColdIonosphericIonsintheMagnetosphere ..............................................................................................219 MatsAndré,SergioToledo-Redondo,andAndrewW.Yau

16Magnetosphere–IonosphereCouplingofPrecipitatingElectronsandIonosphericConductance ...............229 GeorgeV.Khazanov,DavidG.Sibeck,andMikeChu

PartV:TheDynamicMagnetosphere ...................................................................................................................243

17MagnetotailProcesses ..................................................................................................................................245 JoachimBirn,AndreiRunov,andYuriKhotyaintsev

18TheActiveMagnetosphere:SubstormsandStorms .....................................................................................277 YukitoshiNishimuraandLarryR.Lyons

19TheNorthwardIMFMagnetosphere ............................................................................................................293 RobertC.Fear

20ABriefReviewoftheRingCurrentandOutstandingProblems ..................................................................311 RalucaIlie,MuhammadFrazBashir,andElenaA.Kronberg

21Source,Loss,andTransportofEnergeticParticlesDeepInsideEarth’sMagnetosphere(L<4) ..................323 XinlinLi,RichardS.Selesnick,HongZhao,DanielN.Baker,J.BernardBlake,andMichaelA.Temerin

22ThePlasmasphere:ItsInteractionsandDynamics .......................................................................................335 FabienDarrouzet,DennisL.Gallagher,andJohanDeKeyser

23ImpactofIonosphericIonsonMagnetosphericDynamics ..........................................................................353 ElinaA.Kronberg,ElenaE.Grigorenko,RalucaIlie,LynnKistler,andDanWelling

PartVI:PlanetaryMagneticFields ........................................................................................................................365

24PlanetaryMagneticFields .............................................................................................................................367 Karl-HeinzGlassmeierandDanielHeyner

PartVII:InducedMagnetospheres ........................................................................................................................391

25InducedMagnetospheres:Mars ....................................................................................................................393 JasperS.Halekas,JanetG.Luhmann,EduardDubinin,andYingjuanMa

26InducedMagnetospheres:Titan ...................................................................................................................407 CésarBertucci

27BirthofaMagnetosphere .............................................................................................................................427 HansNilsson,EtienneBehar,JamesL.Burch,ChristopherM.Carr,AndersI.Eriksson, Karl-HeinzGlassmeier,PierreHenri,MarinaGaland,CharlotteGoetz,HerbertGunell,and TomasKarlsson

28InducedMagnetospheres:AtmosphericEscape ...........................................................................................441 DavidA.Brain

PartVIII:GiantPlanetMagnetospheres ................................................................................................................453

29TheMagnetodiskRegionsofJupiterandSaturn ..........................................................................................455 NicholasAchilleos,PatickGuio,FlavienHardy,ChrisParanicas,andAriannaM.Sorba

30FastRotatingMagnetospheres:JupiterandSaturnPlasmaSources,LossandTransport ............................471 AbigailM.Rymer

31GasGiantMagnetosphere–Ionosphere–ThermosphereCoupling ................................................................485 LiciaC.RayandJaphethN.Yates

32TheRadiationBeltsofJupiterandSaturn ....................................................................................................499 EliasRoussosandPeterKollmann

33AsymmetricalMagnetospheres:UranusandNeptune .................................................................................515 ChristopherS.ArridgeandCarolPaty

PartIX:Mini-magnetospheresandMoon–MagnetosphereInteractions ...............................................................535

34ADungeyCycleintheLifeofMercury’sMagnetosphere ...........................................................................537 JamesA.Slavin,SuzanneM.Imber,andJimM.Raines

35TheMagnetosphereofGanymede ...............................................................................................................557 XianzheJiaandMargaretG.Kivelson

36OverviewofMoon–MagnetosphereInteractions .........................................................................................575 JoachimSaur

PartX:InvestigatingMagnetosphericProcesses ...................................................................................................595

37GlobalSimulations ........................................................................................................................................597 JoachimRaeder,KaiGermaschewski,WilliamD.Cramer,andJohnLyon

38KineticModelingintheMagnetosphere ......................................................................................................607 StefanoMarkidis,VyacheslavOlshevsky,GáborTóth,YuxiChen,IvyBoPeng,GiovanniLapenta,and TamasGombosi

39Data-BasedModelingoftheEarth’sMagneticField ....................................................................................617 NikolaiTsyganenko,VarvaraAndreeva,MarinaKubyshkina,MikhailSitnov,andGrantStephens

40MultispacecraftMeasurementsInTheMagnetosphere ...............................................................................637 MalcolmW.Dunlop,TieYanWang,XiangChengDong,SteinHaarland,QuanQiShi,HuiShanFu, JohanDeKeyser,ChaoShen,ZhaoJinRong,ChristophePhillippeEscoubet, ZuYinPu,andJonathanEastwood

41ExploringSmallScaleswithMMS ................................................................................................................657 JamesL.BurchandKyoung-JooHwang

42GlobalEnergeticNeutralAtom(ENA)ImagingofMagnetospheres ............................................................673 PontusC.Brandt

43LaboratoryExperiments:PuttingSpaceintotheLab ...................................................................................699 MarkKoepke

PartXI:FutureDirections .....................................................................................................................................715

44ChallengesinModelingtheOuterMagnetosphere ......................................................................................717 GáborTóth,YuxiChen,ZhenguangHuang,andBartvanderHolst

45DoesaMagnetosphereProtecttheIonosphere?..........................................................................................729 RomainMaggioloandHerbertGunell

46SomeUnsolvedProblemsofMagnetosphericPhysics .................................................................................743 MichaelH.Denton

47InstigatorsofFutureChangeinMagnetosphericResearch ..........................................................................753 MichaelW.Liemohn,AmyM.Keesee,L.Kepko,andMarkB.Moldwin Index ......................................................................................................................................................................765 viiiCONTENTS

LISTOFCONTRIBUTORS

TakumiAbe

InstituteofSpaceandAstronauticalScience JapanAerospaceExplorationAgency Sagamihara,Kanagawa,Japan

NicholasAchilleos

DepartmentofPhysicsandAstronomy/ CentreforPlanetarySciences UniversityCollegeLondon London,UK

MatsAndré SwedishInstituteofSpacePhysics Uppsala,Sweden

VarvaraAndreeva

InstituteandDepartmentofPhysics Saint-PetersburgStateUniversity Saint-Petersburg,Russia

ChristopherS.Arridge DepartmentofPhysics LancasterUniversity Bailrigg,Lancaster,UK

DanielN.Baker

LaboratoryforAtmosphericandSpacePhysics UniversityofColoradoBoulder Boulder,CO,USA

MuhammadFrazBashir

DepartmentofElectricalandComputerEngineering UniversityofIllinoisatUrbana-Champaign Urbana,IL,USA

EtienneBehar

SwedishInstituteofSpacePhysics Kiruna,Sweden; and

DepartmentofComputerScience,ElectricalandSpace Engineering

LuleåUniversityofTechnology Kiruna,Sweden

CésarBertucci

InstitutodeAstronomíayFísicadelEspacio UniversidaddeBuenosAires/CONICET BuenosAires,Argentina

JoachimBirn SpaceScienceInstitute Boulder,CO,USA; and

LosAlamosNationalLaboratory LosAlamos,NM,USA

J.BernardBlake SpaceSciencesDepartment TheAerospaceCorporation LosAngeles,CA,USA

JacobBortnik DepartmentofAtmosphericandOceanicSciences UniversityofCalifornia LosAngeles,CA,USA

DavidA.Brain LaboratoryforAtmosphericandSpacePhysics UniversityofColoradoBoulder Boulder,CO,USA

PontusC.Brandt JohnsHopkinsUniversityAppliedPhysicsLaboratory Laurel,MD,USA

RobertoBruno TheNationalInstituteforAstrophysics(INAF) Rome,Italy

JamesL.Burch SouthwestResearchInstitute SanAntonio,TX,USA

ChristopherM.Carr DepartmentofPhysics ImperialCollegeLondon London,UK

TomChang MassachusettsInstituteofTechnology Cambridge,USA

YuxiChen CenterforSpaceEnvironmentModeling UniversityofMichigan AnnArbor,MI,USA

xLISTOFCONTRIBUTORS

MikeChu

NOAA,CooperativeInstituteforResearchinthe Atmosphere ColoradoStateUniversity FortCollins,CO,USA

GiuseppeConsolini

TheNationalInstituteforAstrophysics(INAF) Rome,Italy

WilliamD.Cramer SpaceScienceCenter UniversityofNewHampshire Durham,NH,USA

FabienDarrouzet

RoyalBelgianInstituteforSpaceAeronomy Brussels,Belgium

JohanDeKeyser

RoyalBelgianInstituteforSpaceAeronomy Brussels,Belgium

Michael.H.Denton CenterforSpacePlasmaPhysics SpaceScienceInstitute Boulder,CO,USA; and

NewMexicoConsortium LosAlamos,NM,USA

XiangChengDong SchoolofSpaceandEnvironment BeihangUniversity Beijing,China

EduardDubinin

Max-Planck-InstituteforSolarSystemResearch Katlenburg-Lindau,Germany

MalcolmW.Dunlop SchoolofSpaceandEnvironment BeihangUniversity Beijing,China; and

RutherfordAppletonLaboratory Didcot,Oxfordshire,UK

JonathanEastwood

RutherfordAppletonLaboratory Didcot,Oxfordshire,UK

MariusEchim RoyalBelgianInstituteforSpaceAeronomy Brussels,Belgium; and

InstituteofSpaceScience Magurele,Romania

AndersI.Eriksson SwedishInstituteofSpacePhysics ÅngströmLaboratory Uppsala,Sweden

ChristophePhillippeEscoubet EuropeanSpaceAgency/ EuropeanSpaceResearchandTechnologyCentre Noordwijk,TheNetherlands

RobertC.Fear SchoolofPhysicsandAstronomy UniversityofSouthampton Southampton,UK

HuiShanFu SchoolofSpaceandEnvironment BeihangUniversity Beijing,China

SuiyanY.Fu GeophysicsDepartment PekingUniversity Beijing,China

StephenA.Fuselier SouthwestResearchInstitute SanAntonio,TX,USA; and UniversityofTexasatSanAntonio SanAntonio,TX,USA

MarinaGaland DepartmentofPhysics ImperialCollegeLondon London,UK

DennisL.Gallagher NASAMarshallSpaceFlightCenter Huntsville,AL,USA

KaiGermaschewski SpaceScienceCenter UniversityofNewHampshire Durham,NH,USA

Karl-HeinzGlassmeier InstitutfürGeophysikundextraterrestrischePhysik TechnischeUniversitätBraunschweig Braunschweig,Germany

CharlotteGoetz InstitutfürGeophysikundextraterrestrischePhysik TechnischeUniversitätBraunschweig Braunschweig,Germany

TamasGombosi

CenterforSpaceEnvironmentModeling UniversityofMichigan AnnArbor,MI,USA

ElenaE.Grigorenko

SpaceResearchInstituteof RussianAcademyofSciences Moscow,Russia; and

DepartmentofPhysicsoftheEarth Saint-PetersburgStateUniversity Saint-Petersburg,Russia

PatrickGuio

DepartmentofPhysicsandAstronomy/ CentreforPlanetarySciences UniversityCollegeLondon London,UK; and

DepartmentofPhysicsandTechnology ArcticUniversityofNorway Tromsø,Norway

HerbertGunell RoyalBelgianInstituteforSpaceAeronomy Brussels,Belgium; and DepartmentofPhysics UmeåUniversity Umeå,Sweden

SteinHaarland

BirkelandCentreforSpaceScience UniversityofBergen Bergen,Norway

JasperS.Halekas

DepartmentofPhysicsandAstronomy UniversityofIowa IowaCity,IA,USA

FlavienHardy

DepartmentofPhysicsandAstronomy/ CentreforPlanetarySciences UniversityCollegeLondon London,UK

PierreHenri

LaboratoiredePhysiqueetChimiedel’Environnementet del’Espace

UMR7328CNRS – Universitéd’Orléans Orléans,France

DanielHeyner InstitutfürGeophysikundextraterrestrischePhysik TechnischeUniversitätBraunschweig Braunschweig,Germany

AndrewD.Howarth DepartmentofPhysicsandAstronomy UniversityofCalgary Calgary,AB,Canada

ZhenguangHuang CenterforSpaceEnvironmentModeling UniversityofMichigan AnnArbor,MI,USA

Kyoung-JooHwang SouthwestResearchInstitute SanAntonio,TX,USA

RalucaIlie DepartmentofElectricalandComputerEngineering UniversityofIllinoisatUrbana-Champaign Urbana,IL,USA

SuzanneM.Imber DepartmentofClimateandSpaceSciencesand Engineering UniversityofMichigan AnnArbor,MI,USA; and DepartmentofPhysicsandAstronomy UniversityofLeicester Leicester,UK

XianzheJia DepartmentofClimateandSpaceSciencesand Engineering UniversityofMichigan AnnArbor,MI,USA

JayJohnson DepartmentofEngineering AndrewsUniversity BerrienSprings,MI,USA

TomasKarlsson DepartmentofSpaceandPlasmaPhysics SchoolofElectricalEngineeringand ComputerScience KTHRoyalInstituteofTechnology Stockholm,Sweden

AmyM.Keesee DepartmentofPhysicsandSpaceScienceCenter UniversityofNewHampshire Durham,NH,USA

xiiLISTOFCONTRIBUTORS

LarryKepko

SpaceWeatherLaboratory HeliophysicsScienceDivision NASAGoddardSpaceFlightCenter Greenbelt,MD,USA

GuramKervalishvili

GFZ – GermanResearchCentreforGeosciences Section2.3,Geomagnetism Potsdam,Germany

GeorgeV.Khazanov NASAGoddardSpaceFlightCenter Greenbelt,MD,USA

YuriKhotyaintsev

SwedishInstituteofSpacePhysics Uppsala,Sweden

LynnKistler SpaceScienceCenter UniversityofNewHampshire Durham,NH,USA

MargaretG.Kivelson DepartmentofClimateandSpaceSciencesand Engineering UniversityofMichigan AnnArbor,MI,USA; and

DepartmentofEarth,Planetary,andSpaceSciences UniversityofCalifornia LosAngeles,CA,USA

MarkKoepke DepartmentofPhysicsandAstronomy WestVirginiaUniversity Morgantown,WV,USA; and DepartmentofPhysics UniversityofStrathclyde Glasgow,UK

PeterKollmann

JohnsHopkinsUniversityAppliedPhysicsLaboratory Laurel,MD,USA

PeterKovacs MiningandGeologicalSurveyofHungary Budapest,Hungary

ElenaA.Kronberg MaxPlanckInstituteforSolarSystemResearch Göttingen,Germany; and

DepartmentofEarthandEnvironmentalSciences (Geophysics) LudwigMaximilianUniversityofMunich Munich,Germany

MarinaKubyshkina InstituteandDepartmentofPhysics Saint-PetersburgStateUniversity Saint-Petersburg,Russia

GiovanniLapenta DepartmentofMathematics KatholiekeUniversiteitLeuven Leuven,Belgium

BenoitLavraud InstitutdeRechercheenAstrophysiqueetPlanétologie CNRS,UPS,CNES UniversitédeToulouse Toulouse,France; and

Laboratoired'astrophysiquedeBordeaux CNRS UniversitédeBordeaux Pessac,France

EnsangLee SchoolofSpaceResearch KyungHeeUniversity Yongin,SouthKorea

WenLi CenterforSpacePhysics BostonUniversity Boston,MA,USA

XinlinLi LaboratoryforAtmosphericandSpacePhysics UniversityofColoradoBoulder Boulder,CO,USA; and

DepartmentofAerospaceEngineeringSciences UniversityofColoradoBoulder Boulder,CO,USA

MichaelW.Liemohn DepartmentofClimateandSpaceSciencesand Engineering UniversityofMichigan AnnArbor,MI,USA

NaiguoLin SpaceSciencesLaboratory UniversityofCalifornia,Berkeley Berkeley,CA,USA

YingLiu

KeyLaboratoryforSpaceWeather ChineseAcademyofSciences Beijing,China

JanetG.Luhmann

SpaceSciencesLaboratory UniversityofCalifornia Berkeley,CA,USA

HermannLühr

GFZ – GermanResearchCentreforGeosciences Section2.3,Geomagnetism Potsdam,Germany

JohnLyon DepartmentofPhysicsandAstronomy DartmouthCollege Hanover,NH,USA

LarryR.Lyons

DepartmentofAtmosphericandOceanicSciences UniversityofCalifornia LosAngeles,CA,USA

QianliMa DepartmentofAtmosphericandOceanicSciences UniversityofCalifornia LosAngeles,CA,USA; and CenterforSpacePhysics BostonUniversity Boston,MA,USA

XuanyeMa CenterforSpaceandAtmosphericResearchandPhysical SciencesDepartment Embry-RiddleAeronauticalUniversity DaytonaBeach,FL,USA

YingjuanMa Earth,PlanetaryandSpaceSciences UniversityofCalifornia LosAngeles,CA,USA

RomainMaggiolo RoyalBelgianInstituteforSpaceAeronomy Brussels,Belgium

WieslawMacek SpaceResearchCentre PolishAcademyofSciences Warsaw,Poland

StefanoMarkidis KTHRoyalInstituteofTechnology Stockholm,Sweden

MarkB.Moldwin DepartmentofClimateandSpaceSciencesand Engineering UniversityofMichigan AnnArbor,MI,USA

KyleR.Murphy NASAGoddardSpaceFlightCentre Greenbelt,MD,USA; and DepartmentofAstronomy UniversityofMaryland CollegePark,MD,USA

KaleviMursula DepartmentofPhysics UniversityofOulu Oulu,Finland

TakumaK.M.Nakamura SpaceResearchInstitute AustrianAcademyofSciences Graz,Austria; and InstituteofPhysics UniversityofGraz Graz,Austria

YasuhitoNarita SpaceResearchInstitute AustrianAcademyofSciences Graz,Austria

TsugunobuNagai InstituteofSpaceandAstronauticalScience JapanAerospaceExplorationAgency Sagamihara,Japan

HansNilsson SwedishInstituteofSpacePhysics Kiruna,Sweden

YukitoshiNishimura DepartmentofElectricalandComputerEngineeringand CenterforSpacePhysics BostonUniversity Boston,MA,USA

KatariinaNykyri CenterforSpaceandAtmosphericResearchandPhysical SciencesDepartment Embry-RiddleAeronauticalUniversity DaytonaBeach,FL,USA

xivLISTOFCONTRIBUTORS

VyacheslavOlshevsky KTHRoyalInstituteofTechnology Stockholm,Sweden

ChrisParanicas

JohnsHopkinsUniversityAppliedPhysicsLaboratory Laurel,MD,USA

Georges.K.Parks SpaceSciencesLaboratory UniversityofCalifornia,Berkeley Berkeley,CA,USA

CarolPaty DepartmentofEarthSciences UniversityofOregon Eugene,OR,USA

IvyBoPeng LawrenceLivermoreNationalLaboratory Livermore,CA,USA

WilliamK.Peterson LaboratoryofAtmosphericandSpacePhysics UniversityofColoradoBoulder Boulder,CO,USA

FerdinandPlaschke SpaceResearchInstitute AustrianAcademyofSciences Graz,Austria

ZuYinPu SchoolofEarthandSpaceSciences PekingUniversity Beijing,China

JoachimRaeder SpaceScienceCenter UniversityofNewHampshire Durham,NH,USA

JimM.Raines DepartmentofClimateandSpaceSciencesand Engineering UniversityofMichigan AnnArbor,MI,USA

LiciaC.Ray DepartmentofPhysics LancasterUniversity Lancaster,UK

ZhaoJinRong InstituteofGeologyandGeophysics ChineseAcademyofSciences Beijing,China

EliasRoussos MaxPlanckInstituteforSolarSystemResearch Goettingen,Germany

AndreiRunov DepartmentofEarth,Planetary,andSpaceSciences UniversityofCalifornia LosAngeles,CA,USA

AbigailM.Rymer JohnsHopkinsUniversityAppliedPhysicsLaboratory Laurel,MD,USA

JoachimSaur InstitutfürGeophysikundMeteorologie UniversityofCologne Cologne,Germany

RichardS.Selesnick SpaceVehiclesDirectorate AirForceResearchLaboratory KirtlandAFB,NM,USA

ChaoShen HarbinInstituteofTechnology Shenzhen,China

QuanQiShi InstituteofSpaceSciences ShandongUniversity Weihai,China

DavidG.Sibeck NASAGoddardSpaceFlightCenter Greenbelt,MD,USA

MikhailSitnov JohnsHopkinsUniversityAppliedPhysicsLaboratory Laurel,MD,USA

JamesA.Slavin DepartmentofClimateandSpaceSciencesand Engineering UniversityofMichigan AnnArbor,MI,USA

AriannaM.Sorba DepartmentofPhysicsandAstronomy/ CentreforPlanetarySciences UniversityCollegeLondon London,UK

DavidJ.Southwood SpaceandAtmosphericPhysics ImperialCollege London,UK

GrantStephens JohnsHopkinsUniversityAppliedPhysicsLaboratory Laurel,MD,USA

MichaelA.Temerin SpaceSciencesLaboratory UniversityofCalifornia Berkeley,CA,USA

RichardM.Thorne DepartmentofAtmosphericandOceanicSciences UniversityofCalifornia LosAngeles,CA,USA

SergioToledo-Redondo InstitutdeRechercheenAstrophysiqueetPlanétologie CNRS,UPS,CNES UniversitédeToulouse Toulouse,France

GáborTóth CenterforSpaceEnvironmentModeling UniversityofMichigan AnnArbor,MI,USA

KarlheinzJ.Trattner LaboratoryforAtmosphericandSpacePhysics UniversityofColoradoBoulder Boulder,CO,USA

NikolaiTsyganenko InstituteandDepartmentofPhysics Saint-PetersburgStateUniversity Saint-Petersburg,Russia

BartvanderHolst CenterforSpaceEnvironmentModeling UniversityofMichigan AnnArbor,MI,USA

ZoltánVörös SpaceResearchInstitute AustrianAcademyofSciences Graz,Austria

TieYanWang RutherfordAppletonLaboratory Didcot,Oxfordshire,UK

AnnaWawrzaszek SpaceResearchCentre PolishAcademyofSciences Warsaw,Poland

DanWelling DepartmentofPhysics UniversityofTexasatArlington Arlington,TX,USA

ZhongweiW.Yang KeyLaboratoryforSpaceWeather ChineseAcademyofSciences Beijing,China

JaphethN.Yates EuropeanSpaceAstronomyCentre EuropeanSpaceAgency Madrid,Spain

AndrewW.Yau DepartmentofPhysicsandAstronomy UniversityofCalgary Calgary,AB,Canada

EmiliyaYordanova SwedishInstituteofSpacePhysics Uppsala,Sweden

HongZhao LaboratoryforAtmosphericandSpacePhysics UniversityofColoradoBoulder Boulder,CO,USA

PREFACE

Introducedin1958,thetermmagnetosphererefersto themagneticcavitysurroundingacelestialbody.Invisible tothehumaneyes,magnetospherescanonlybeexplored throughthedevelopmentofinstruments,theoriesand numericalmodels.Withtheadventofthespaceagewe havestartedexploringtheminsituandaccumulatedan impressiveamountofdataovertheyears.Sixtyyearsafter thetermmagnetospherewasbeendefined,itischallengingtoreviewtheexistingknowledgeonsolarsystemmagnetospheresinonesinglebook.

Thisbookprovidesanoverviewofthemagnetospheresin thesolarsystem,fromthesmallinducedmagnetospheres thatformaroundunmagnetizedbodiestothelargemagnetospheresofthegiantplanets.Magnetospheresarehighly complex,structuredandtime-dependentsystemsconstantlyinteractingwiththesolarwindandthecomponents oftheplanetarysystems,suchastheirionosphere,atmosphere,surface,rings,andmoons.Eachmagnetosphereis uniqueandcontainsvariousintertwiningsubregions,particlepopulations,andplasmaprocesses.Thisexplainsthe scientificinterestofmagnetosphericphysics:magnetospheresareaccessiblenaturallaboratoriesforstudyingfundamentalphysicalprocessesofuniversalapplication. Moreover,theEarth’smagnetosphereisakeycomponent ofournear-spaceenvironmentonwhichourmodernsocietiesareincreasinglydependent.

Thebookisdividedinelevensectionsthatcoverthe currentstateofourunderstandingaswellasfuturedirectionsforscientists.PartIstartswithabriefhistoryofmagnetospheresandpresentsthebasicprinciplesand equations.PartIIaddressesthefundamentalprocesses thatgovernmagnetosphericphysics.Thethreefollowing sectionsarededicatedtotheEarth’smagnetosphere,the moststudiedandbestknownofthesolarsystemmagnetospheres.Theyrespectivelyfocusonitscouplingwiththe Earth’sionosphere(partIII),itscouplingwiththesolar wind(partIV),anditsdynamics(partV).Thenextsections areorientedtowardothersolarsystembodies.Aftera discussionaboutplanetarymagneticfieldsinpartVI,we focusontheinducedmagnetospheresinpartVII,onthe

magnetospheresofgiantplanetsinpartVIIIand,in partIX,on “minimagnetospheres”,suchasthoseof Mercuryandmagnetizedmoons.PartXconsidersthetools thatareusedtoinvestigatemagnetosphericprocesses. Finally,partXIdiscussesthekeyquestionsandchallenges tobeaddressedinthecomingyears,providingsome insightsonthefuturedevelopmentsofmagnetospheric research.Thechapterscontainedhereinincludecontributionsfromexperimentalists,theoreticians,andnumerical modelers.

Wehopethatthisbookwillbearesourceforboththe noviceresearcherandtheexperiencedscientist.Forthose lessacquaintedwithcurrenttopicsinEarthandplanetary magnetosphericresearch,thisbookwillprovidethebackgroundmaterialrequiredtobeknowledgeableonthe currentstateoftheart.Forexperts,itwillactasareferencetothemostimportantmagnetosphericsciencebreakthroughsandhelpexpandthereader’shorizonswithits coverageofthediversenear-bodyregionsinspace.With thisbook,wehopethatthereaderwillcomprehendmost ofthefeaturesofmagnetospheresandfindthekeysto delveasfaraspossibleintothem.

Wegratefullyacknowledgesupportandguidancefrom RituparnaBoseandDanielFinchofJohnWiley&Sons, Inc.throughthebookproposalprocess,theexternalpeer reviewofthechapters,andthebookproductionprocess. Wealsothankalltheauthorsfortheircontributionandall thereviewersfortheirassistance.

ThisbookisdedicatedtothememoryofRichardM. Thorne.

RomainMaggiolo RoyalBelgianInstituteforSpaceAeronomy, Belgium

NicolasAndré ResearchInstituteinAstrophysics andPlanetology,France

HiroshiHasegawa JapanAerospaceExplorationAgency,Japan

DanielT.Welling UniversityofTexasatArlington,USA

TheEarthMagnetosphere

1

ABriefHistoryoftheMagnetosphere

DavidJ.Southwood

ABSTRACT

TheearlyhistoryofthemagnetosphereistakenfromtheearliestsuggestionsofamaterialtransportbetweenSun andEarthbySabineinthenineteenthcentury,throughtheworkofbothBirkelandandChapmanandcoworkers intheearlytwentiethcenturytothenamingofthemagnetosphere,theproposaloftheopenmagnetosphere,and thediscoveriesofthefirstdecadeandahalfofthespaceage.

1.1.INTRODUCTION

Onecouldbeginahistoryofthemagnetosphereasearly as1600whenGilbertpublishedhis “DeMagnete,” which firsttreatedthemagnetismoftheEarthashavingan embeddedplanetarydipole.Alternatively,onecouldstart withthecoiningofthetermbyThomasGoldintheearly spaceagein1959.AsneitherGilbertnorGoldreallyunderstoodwhatturnedouttobethemostsensitiveandbasicscientificissues,itisprobablyagoodcompromisetostart withEdwardSabinein1852(Sabine,1852).Inhisreport totheRoyalSocietyofLondon,Sabinewasthefirstto glimpsedimlythenatureoftheelectromagneticcoupling betweentheSunandEarththatisfundamentaltoboth theformationofthemagnetosphereandalsoitsactivity.

1.2.BRITISHWORKINTHENINETEENTH CENTURY

EdwardSabinewasabothscientistandasoldier,in thelattercapacityseeingserviceinNorthAmericain theWarof1812.Hisinterestingeophysicsstemmedinitiallyfromworkingingeodesy.Hemovedfrommeasuringterrestrialgravitytothestudyoftheterrestrial magneticfield,whichherealizedneededtobesurveyed

SpaceandAtmosphericPhysics,ImperialCollege, London,UK

globally.Nodoubtafterpointingouttohissuperiorsina maritimenationwithaglobalempiretherelevanceof understandingthemagneticfieldfornavigationalpurposes,ColonelSabinesetupmagneticobservatories acrosstheglobe.His1852paperreportsresultsonthe variationofthefieldwithtimeatthewidelyseparated locationsofTorontoandHobarton(nowHobart,Tasmania).Diurnalvariationsareseenbutalsothereare disturbancesdetectedatbothsiteswidelyseparatedin longitudeandlatitude.Themostimportantcomment hemakesforourpurposeistorelatehisresultstothose ofaGermanastronomer,HeinrichSchwabe,whohad proposedfromalongrecordofsolarobservationsthat sunspotsexhibitedaregular11yearcycle.Sabinenoted thatthevariationinglobalmagneticactivityappearedto matchSchwabe’ssunspotperiod.Hefurthernotedthat Schwabehadfailedtodetectanychangeinterrestrialclimateonthesamescale.Hethengoesontomaketheprescientremark “Butitisquiteconceivablethataffections ofthegaseousenvelopeoftheSun,orcausesoccasioning thoseaffections,maygiverisetosensiblemagnetical effectsatthesurfaceofourplanet,withoutproducingsensiblethermiceffects ” Theword “sensible” hereisinthe (archaic)senseof “detectable ” . Thefirstobservationsofwhatwenowknowtobea directcorrelationbetweenasolarphenomenonandageomagneticresponsecamewithinafewyears.In1859a globalmagneticdisturbanceoccurred,nowcalledthe

SpacePhysicsandAeronomyCollectionVolume2:MagnetospheresintheSolarSystem,GeophysicalMonograph259,FirstEdition. EditedbyRomainMaggiolo,NicolasAndré,HiroshiHasegawa,andDanielT.Welling. ©2021AmericanGeophysicalUnion.Published2021byJohnWiley&Sons,Inc. DOI:10.1002/9781119815624.ch1

Carringtonstorm(Carrington,1860).Thereisanironyin thisattribution.WhatCarringtonactuallyreportedtothe RoyalAstronomicalSocietywasthefirstobservationof whitelightflaresontheSun.Inhisreporthedoesrefer toanalmostsimultaneousmagneticdisturbancefollowed about17hourslaterbylargemagneticdisturbances.The observationswouldhavebeenprovidedbyBalfourStewartandcamefromKew(nearLondon)(Stewart,1860).In thediscussionofthemagneticobservations,Carrington wasaskedwhethertherewasadirectrelationshipbetween themagneticdisturbancesandtheextremesolarevent;he repliedcautiously “…. Whilethecontemporaryoccurrence maydeservenoting,hewouldnothaveitsupposedthathe evenleanstowardshastilyconnectingthem.Oneswallow doesnotmakeasummer. ” (Carrington,1860).Balfour Stewart(1860)reportedonthemagneticeventsandhad nosuchcaution.Extendedmagneticdisturbanceswere recordedgloballybetween28Augustand2September 1859.Hepointedoutthatauroraldisplayswereseenin partsoftheBritishEmpire(e.g.intheCaribbean,in India)wheretheyhadneverbeenseenbeforeorsince. Inhisreportonthosedisturbances,hedescribedCarrington’sobservationsbutaftergentlycriticizingCarrington ’ s caution,heinvokedspecificallySabine ’searlierresult. “SinceGeneralSabinehasprovedthatarelationsubsists betweenmagneticdisturbancesandsunspots,itisnot impossibletosupposethatinthiscaseourluminarywas takenintheact ” RemovingtheBritishunderstatement, thisstatementdirectlysupportsthenotionofaSun–Earth connection.

Thequasi-instantaneoussignalwouldhavebeendueto modificationoftheionosphericconductivitybyincident X-rayandUVradiation,thusenhancingthemagneticsignalsassociatedwiththedailydynamomotionintheionosphere.Thedelayedsignalwouldhavebeentheshockof flarematerialarrivinganddisruptingthemagnetosphere. Itwouldbeyearsbeforetheseexplanationsbecamecommoncurrency.

Carrington ’scautionreflectedthetenorofthetimes.In thatera,KelvinandRayleighruledtheBritishscientific roostandneitherscientistwasinclinedtoacceptthat materialcouldmovedirectlythroughspacefromSunto Earth.DespitehisreferringdirectlytoSabine’s(1852) resultandtheeventsof1859,Kelvin’sassessmentwas madeclearinhispresidentialaddresstotheRoyalSociety in1892(Kelvin,1892).

Southwood(2015)creditsStewartwithkeepingalive theideathattheremightbeamaterialconnectionbetween theSunandEarthfollowingCarrington’sreport.Aswe seelater,itwascarriedforwardbyhisstudentArthur Schuster.Schusteralsodidmuchtoelucidatesolarand lunarpatterns.Usingfourmagneticstations,Schuster andLamb(1889)providedthebasicbreakdownofthe regularmagneticdiurnalpatternsofdisturbancefixed withrespecttotheSunandalsoalunarcomponent

originallyidentifiedbySabine(1861).However,bythe endofthenineteenthcenturythereremainedanopen questionoverthelargestglobaldisturbances,whichshow noobviouslinkwithtimeofdaybutdidvaryinintensity overthesolarcycle.Thecodificationofthelunar(L)and Solar(Sq)quietdaycurrentpatternswasundertakenby SydneyChapman(1913)usingmuchmorecoverage(21 stations)(Matsushita,1968).Theglobalmagneticpattern forthemagneticallydisturbedperiodsorgeomagnetic stormswasalsodistinctive.Thepatternwascalledthedisturbancesystem(SD or DS).Followingalargeamountof magneticsurveyworkfortheBritishRoyalObservatory, Chapman(1919)publishedapaperoutliningthemagnetic disturbancepatternsandcontainingwhatisthefirst attemptbyaBritonforatheory.However,beforewelook atwhathesaidandwhereitled,oneshouldnotethatthere hadbeenmuchearliersuggestionsconcerningthesource ofgeomagneticdisturbancesandtheauroraetheybringin theirwake.

1.3.SCANDINAVIANWORKINTHE NINEETEENTHCENTURY

TheBritishanalysisofmagn eticdisturbanceswasstatistical.Itwasassumedthatthesignalsoriginatedin motionofaconductingpartoftheatmosphere.The synchingofsignalswithlunarorsolarphasemakesa statisticalapproachnatural.Unsurprisingly,Chapman wantedtolookatthedistu rbedmagneticsignalsina similarway.ThiswasnottheapproachoftheScandinavianswholivedundertheauroraandsawitnight bynight.

KristianBirkelandisoneofNorway’sgreatestscientists.Hewasbornin1867inKristiania,latertobecome Oslo.Fromacomfortablebackground,hisexceptional natureshowedearlyon.AfteruniversityinKristiania, in1893,helefttogotoParistostudyattheEcolePolytechniquewherehisinitialinterestwasinthenewscience ofelectromagnetismcomingfromMaxwell’sunifying equations.AftertravelelsewhereinEuropehereturned toNorwaytobecometheyoungestprofessorintheuniversityinKristiania.

EvenforaNorwegianfromasfarsouthaspresent-day Oslo,theauroraisanaturalinterest.Untilthenineteenth centurytheaurorawasoftenassumedtobeanatmosphericeffect.Despitetheconcurrentauroraldisturbances inthegreatmagneticstormof1859referredtoabove,the questionofauroraloriginandanyelectromagneticeffect orlinktotheSunappearsnottohavebeenexamined muchfurtherintheUK.ItwasBirkelandwhopicked upthescientificchallengeofexplainingtheaurora.

Birkeland’slifeandworkareablydiscussedinEgeland andBurke’smonograph(EgelandandBurke,2005). WhenhereturnedtoNorway,Birkelandwasthoroughly

groundedinelectromagnetismandexperimentaltechnique.Moreover,hewaswellawareofthenewdiscovery oftheelectronbyJ.J.Thompsonin1897.Hesuspected thatthisnewphysicsmaycontainanexplanationofauroralorigin.Neveramantoshyfromexperimentalworkor observation,heorganizedaseriesofexpeditionstonorthernNorwayandarrangedsubsidiaryobservationselsewhereinRussiaandIceland.Althoughthefirst expeditionwasabandonedthroughextremeweather, theworkestablishedovertimeavastbodyofobservations documentedinaseriesofvolumes(Birkeland,1901,1908, 1913).Theheightoftheaurorawasshowntobearound 100km.Theelectromagneticnatureoftheauroraitself wasfirmlyestablishedbyshowingthathorizontalcurrents,theauroralelectrojet,flowintheactualdisplays. Birkelandspeculatedthatthesourceoftheaurorallight isduetoelectronsofextraterrestrialoriginimpacting theupperatmosphere.HehadconstructedamodelEarth inavacuumchamber(aterrella)andonexposingittoa beamofelectronssucceededincreatingaringoflight aroundthemagneticpoles,mimickingtheshapeofthe actualauroralzone.Hesentapaperto Nature advancing hisideathattheaurorarepresentsincidentbeamsofelectronsofsolarorigin.Atthispoint,fateintervenedasthe paperwassenttoArthurSchustertoreferee.Schuster recommendedrejectionashepointedoutthatthebeam ofnegativelychargedparticleswouldbequenchedby anelectricfieldastheSunwouldchargepositiveand theEarthchargenegative.Birkelandrecognizedthat theargumentwascorrectandimmediatelymodifiedthe ideatoproposeanelectricallyneutralstreamofcharged particlesfromtheSun,i.e.whatisnowcalledplasma.Possiblystungbytherejection,Birkelandneverresubmitted themodifiedideato Nature butincludeditintheformal reportsoftheexpeditions.Thereportpublishedin1908 (Birkeland,1908)includedasketchlikethatreproduced inFigure1.1(fromSouthwood,2015).Diagramssuch asthis,showingdownwardcurrententeringtheupper atmosphereatonelongitude,flowingthroughithorizontallyandleavingbyanupwardreturncurrentataseparatelongitude,arenowcommonplace.Birkelandhad madethefirstsketchofthethree-dimensionalelectrical currentsystemofanauroraldisturbance.Thesketch wouldberecognizedtoday.

1.4.SCHISM

Nature isaBritishjournaland,intheearlyyearsofthe twentiethcentury,Britainwaspossiblythemostimportantscientificnation.ItseemslikelythathadBirkeland’ s correctedideabeenpublishedintheBritishliterature,it mighthaveforestalledwhatbecameamajorschismin thesciencecommunity.PartoftheproblemwasphilosophicalbutSouthwoodandBrekke(2017)suggestthat

Figure1.1 ReproductionfromSouthwood(2015)ofthesketch onp.105ofVolume1ofBirkeland’sreportonthe1902–1903 polarexpeditions(Birkeland,1908).Itisnotquiteclearin Birkeland’stext,butthedottedanddashedlinesrepresentthe streamingchargesofoppositesigninachargeneutralstream fromtheSun.

partwaspersonalembarrassmentforamanwhowasfast becomingthedominantBritishnameinthefield.As alreadynoted,Chapman(1919)hadmadeamajoranalysisofmagneticdataassociatedwithwhathadbeenidentifiedasthedisturbedtimecurrentsystem.However,the paperincludedanappendixthatputforwardthesame ideathatBirkelandhadoriginallypropoundedmorethan adecadebefore.Chapmanproposedthatthedisturbances wereduetoelectronsincidentontheatmosphere.The errorwascaughtrapidlyafterpublicationbyLindemann (1919),whopublishedacritiqueeffectivelysuggesting,as Birkelandhaddonealready,thattheremightbeaneutral streamofpositiveandnegativelychargedparticlesfrom theSun.Southwood(2015)pointedoutthat,although ChapmanwasmostlikelyunawareofBirkeland’sidea, Schuster(1911)appearedtohavegraspedtheidea.However,after1919,Britishreferences[andevenAmerican references(e.g.Parker,1969)]attributetheneutralstream notiontoLindemann.

TheantipathybetweentheBritishandScandinavian schoolscontinuedforaround40yearsuntilsophisticated resultsfromspacebroughtittoanend.Thediscussionby Fukushima(1994)isinformative.Chapmanfeltstatistical informationwasfundamental.Healsohadamathematicalreasonforignoringthepossibilityofcurrentsflowing intoandoutoftheupperionizedatmosphere,theionosphere.Itwasauniquenesstheorem.ThemagneticperturbationsrecordedonthesurfaceoftheEarthcouldalways beattributedtoauniquesetofcurrentsintheconducting

ionosphereifitwasassumednocurrentflowedinandout ofthetopoftheionosphere.Foranygivenfieldpattern thesewerereferredtoastheequivalentcurrentsystem. Therehad,nonetheless,beenworkbyVestineandChapman(1938)thatpurportedtoshowthatthepurelyhorizontalcurrentmodelofChapmanfitteddatabetter. Fukushima(1969)showedthatthemodelproposedby VestineandChapmantorepresentthatofBirkeland wassomewhatunreasonable.Changingtheassumption tosomethingmorerationalrevealedthattherewaslittle tochoosebetweenthesystems.Fukushima(1971)further showedexplicitlythatthecurrentsystemabovetheionosphereisshieldedfromtheground,i.e.undetectable.

1.5.CHAPMAN–FERRARO:ACAVITYIN ASTREAMOFCHARGEDPARTICLESFROM THESUN

In1927,V.C.A.Ferrarobeganpostgraduatestudywith ChapmanatImperialCollegeLondon.Chapman’searlier workhadshownthatageomagneticstormbeganwithan increaseofthemagneticfieldworldwide.Thedelay betweenevidenceofanythingoccurringontheSunand thearrivalemphasizedthatthesolar–terrestrialconnection wasnotthroughelectromagneticradiationbutwastransmittedviamaterial(corpuscular)means.Chapmangave Ferrarothemagneticstormproblemtostudy(Ferraro, 1969).HewastoexaminetheeffectofaneutralunmagnetizedstreamofchargedparticlesfromtheSunimpingingon theterrestrialmagneticfield(ChapmanandFerraro,1930, 1931,1932,1933).Thetheoryprecededanynotionofmagnetohydrodynamicsandfrozen-inmagneticfield;space betweentheEarthandtheSunwastreatedasunmagnetized.Thestreamwasshowntoenclosethegeomagnetic fieldinacavity.Thiswasthefirstidentificationofaterrestrialmagneticdomainthatwouldeventuallybenamedthe magnetosphere.Thegeomagneticfieldcavitywasbounded byacurrentsheetnowcalledthemagnetopause.Theconfinementoftheterrestrialfieldwithinabubblewithinthe streamwellexplainedtheexistenceofaterrestrialmagnetic cavity,whoseinternalfieldwouldincreaseifincreasedoutflowoccurredfromtheSun.Themathematicalsolution usedtoillustratethemagneticconfinementusedatwodimensionalimagedipole,asshowninFigure1.2.30years later,JimDungeypublishedananalytictwo-dimensional solutionoftheChapman–Ferraroproblemin1961 (Dungey1961a).Bythen,computershadadvancedenough thatthree-dimensionalnumericalsolutionswereaboutto appear(SpreiterandBriggs,1962).

Unfortunately,asitstood,theChapman–Ferraro modeldidnotexplainmuchmoreaboutmagneticstorms thantheincreaseinglobalfieldatstormonset.Onefeature ofthemodelisthepointsmarkedQinFigure1.2,wherethe

Figure1.2 TheChapman–Ferrarocavity.Reproductionof ChapmanandFerraro’ssketchofthenoon–midnightmeridian oftheenclosureoftheEarth’sfieldbyaneutralstreamof solarchargedparticles.Thefieldpatternshownisproduced byanimagedipoleonthelefthandside.ThelettersQmark magneticneutralpointsontheboundary.

fieldgoestozero.Itwasrecognizedthatparticlesmight enterthecavityhereandguidedbythefieldwouldimpinge ontheatmosphereataurorallatitudes.Nevertheless, althoughthelatitudewasright,therewasnomechanism toexplainhowtheaurorawasseenonthenightside.

Asecondmajorproblemwasthataftertheinitial increaseinterrestrialfieldinthemainphaseofageomagneticstorm,thefieldwasdepressedgenerallybyamuch largeramountthantheinitialenhancement.Daglis etal.(1999)notethatthedepressionofthefieldinthe mainphasehadbeenknownsincethenineteenthcentury. (Fitzgerald,1892),Chapman(1919),and,twoyearsearlier,Schmidt(1917)hadsuggestedthatthedepression wasduetosolarchargedparticlesencirclingtheEarth. ChapmanandFerraro’stheorydidproposethatsolar particlessomehowprogressivelypenetratedtotheterrestrialmagneticcavitysothatthecurrentbuiltupbut understandingwouldreallyonlyarriveonceasignificant externalfieldwasallowedfor.

1.6.ALFVÉN:THEORYOFSTORMSANDTHE ADVENTOFMAGNETOHYDRODYNAMICS

Inthe1940s,HannesAlfvénandhisresearchgroup basedinStockholmbecamethemajorproponentsof theScandinavianschool.

Alfvén(1939,1940)proposedanewstormmodel focusedonexplainingtheaccessofchargedparticlesto maketheringcurrentandtheaurora.Itwaswrong,partly duetoacompleterejectionofChapman’sideas.The

stream of charged solar particles

theoryassumedthatamagnetizedincidentchargedparticlestreamwasabletosimplyflowontotheEarthfield.In otherwords,therewasnoallowanceforamagnetopause.

AlfvénhimselfwasagreatadmirerofBirkelandandthe modeldoesresembleadevelopmentofhisideas.Themodel alsointroducedtheimportantideaoftherebeinganelectric fieldwithintheterrestrialenvironmentduetothesolar interaction,effectivelyplacingavoltageimposedfromoutsideontheterrestrialsystem.Theinducedelectricfield meantthattherewasapotentialforthesolarmaterialto doworkontheterrestrialsystem.Inpractice,theabsence ofinclusionoftheeffectsthatcausethemagnetopauseto formmeantthatAlfvén’selectricfieldwasinthewrong direction.Nevertheless,itsintroductionwasimportant.

In1942,Alfvénmadeanenormousstepinashort Nature paper(Alfvén,1942),whichintroducedtheidea ofthemagneticfieldbeingfrozenintoaperfectlyconductingmediumlikeaplasma.Thisisseenastheinventionof magnetohydrodynamics(MHD).ItexplainedthemagnetizednatureofanyplasmaflowingfromtheSun(asAlfvén’sstormmodelrequired)butitalsogaveanintuitive waytoseetheformationofacurrentsheetormagnetopausebetweensolarandterrestrialplasma(whichAlfvén’sstormmodelhadignored).

1.7.THESPACEAGEBEGINS

TheChapman–Ferraromodelmadeitappeartoohard forsolarplasmatoentertheterrestrialmagneticenvironmentandAlfvén’sappearedtomakeittooeasy.Itwas anothertwentyyearsbeforetheseedsofwhatisnow thegenerallyacceptedmodelweresown.Bythattime thespaceagehadbegunandmuchnewinformation wasemerging.

Atthebeginningofthe1950s,Biermann(1951)had deducedthepresenceofthesolarwindfromthebehavior ofcomettails.Parker(1958)furtherexplainedthatnot onlywasitsflowsupersonicbutalsoitwouldbemagnetized.In1958also,themagnetospherereceiveditsname fromGold(1959).Gold’spaperwasmotivatedbythefirst majordiscoveryofthespaceage,theVanAllenradiation belts(VanAllenandFrank,1959).Despitethefactthat retrospectivelyitwasseenthatSputnik2hadmeasured them(Dessler,1984),thefirstreportswerefromthefirst USEarthorbitingspacecraft,Explorer1.Outinspaceit wasfoundthatthedistantmagneticdipolefieldofthe Earthwasadequatetotrapalargeamountofenergetic chargedparticles.Gold(1959)introducedaveryimportantconcept,theinterchangemotionoffluxtubes.Unfortunately,becauseheattributedthechargedparticlestoa sourcenearEarth[thecosmicrayalbedoneutrondecay theory,CRANDseee.g.Singer(1958),Vernovetal., (1959)],hispaperwasinerror.HeproposedthatthecreationofradiationbeltparticlesnearEarthwouldinducea

naturaloverturningmotioninmagnetosphericmagnetic fluxtubeswhereindensertubesmoveoutwardsandemptiertubesmovein.TheCRANDsourcecanremainrelevanttothehighestenergyparticles(seee.g.Lietal., 2017).However,mostoftheradiationbeltparticlesand thelowerenergyparticlesthatareresponsibleforcarrying theringcurrentoriginatefromthesolarenvironment. Kellogg(1959)firstsuggestedasolarsourcefortheVan Allenparticles.Theexternalsourcemeansthattheparticlesareinjectedandenergymustbesuppliedfortheinjectionprocess.Thisisadriveninterchangemotion(cf. SouthwoodandKivelson,1989).Theenergyisinpractice providedfromthesolarwindthroughpartoftheBirkelandcurrentsystemdiscussedlater.

Alsoin1959,DesslerandParker(1959)madeamajor breakthroughinunderstandingthemainphaseofgeomagneticstorms.Theyproposedthatsolarplasmaentry tothemagnetospherewasenhancedfollowingtheinitial compressionofthemagnetosphereatthestartofastorm becausetheboundaryofthemagnetospherewouldbe unstable.Theythenderivedarelationbetweenthedepressioninthefieldandtheenergyofthechargedparticles trappedinthemagnetosphericfieldfortwospecialphase spacedistributionsofparticles,whichwasgeneralizedby Sckopke(1966).Theideaofenhancedsolarparticleentry duringmainphaseproducingaringcurrentaroundthe Earthwasrightbuttheentryprocessremainedtobe identified.

Weshallreturntodiscussparticleinjectionandtransportafterintroducingtheopenmagnetosphere modelnext.

1.8.DUNGEY:THEOPENMAGNETOSPHERE

Dungeyfreelyadmittedthathisopenmagnetospheric model(Dungey1961b)wasinspiredbythesimilarity betweentheionospheric DS disturbedtimecurrentpatternandthemotioninastirredcupofcoffee(Stern, 1986).Ashestirredmilkintothecoffeebymovinghis spoonacrossthecenterofthecuphenotedthecirculation patternresembledthatinFigure1.3.

DungeyhadstudiedforaPhDtenyearsearlierworking onanideaofHoyle’sthatauroraemightoriginatefrom accelerationatmagneticneutrallinesthatwouldform betweenaterrestrialdipolefieldandauniformexterior field(Stern,1986).Cruciallyherealizedin1960thatthe magneticconfigurationwouldallowthesolarwindto drivethefamiliarDScurrentsystemintheionosphere.

By1960,MHDwasthewaypeoplethought;thefrozenfieldideaisbuiltintoDungey’smodel.However,MHDis anapproximationandwillbreakdownwhereverthefield isverysmallorvariesrapidlyonthescaleofchargedparticleLarmorradii.Reconnectioncorrespondstooneform ofbreakdown.Dungey’ s doctoralwork(Dungey,1950)

Figure1.3 TheionosphericDSflowpattern.Theantisunward motionathighlatitudesandthereturnatremindedDungey ofthepatternfromstirringcoffee.

hadintroducedtheideaofmagneticreconnection.Near neutralpointsinthemagneticfield,thefrozen-infieldis nolongervalidandfieldlinescanbe “broken.” Thefinal elementofthenewmodelwasmagneticreconnection.

Figure1.3reproducesanidealizedformoftheionosphericflowshowingthe DS pattern.Thesketchisapolar viewofthenorthernhemispherewiththedashedlines representingtheionosphericplasmastreamlinesdeduced fromthemagneticperturbationsmeasuredattheEarth’ s surface.Thereisatwinvortexflow.Thedottedboundary markswheretheflowswitchesfromsunwardontheequatorwardsidetoantisunwardpoleward.Dungeysuggested thatsunwardmomentumwastransferredalongthemagneticfieldtodrivetheantisunwardflowinthepolar region.Therewouldbeareturnsunwardflowatlowlatitudes.Theflowrepresentsequipotentialsoftheionosphericelectricfield.Itisimportanttonotethatthe electricfieldinducedinthelowlatitudesubauroral regionsisoppositetothatproposedbyAlfvén(1940) andtheflowisoppositetowhatwouldhavebeentheoverallpatternproducedbytheGold(1959)mechanism.

Figure1.4showsthecirculationoffluxtubesinthe noon–midnightmeridianintheopenmodel.Thefigure isshownwithasouthwardinterplanetaryfieldcomponent,thesimplestcaseasitissymmetric.Themagnetic fieldthreadsthemagnetopauseshownbythedashedline. Throughouttheflowismarkedbywhitearrowsinthe

Figure1.4 Dungey’sopenmagnetosphere.Thesimplestcaseofapurelysouthwardinterplanetaryfield(IMF)is assumed.Thesketchisdrawninthenoon–midnightmeridian.Thedashedcurverepresentsthemagnetopause. Thedarkarrowsrepresentthesolarwindflow,openarrowstheflowinducedintheterrestrialenvironment. DaysideandnightsidemagneticreconnectionoccursatthelocationsindicatedbyX.Thenumbersrepresent theenvisagedfieldlinemotionsequenceinsteadystate:solarwind(1),daysidereconnection(2),polarcap connection(3),tailreconnection(4),nightsideinwardmotion(5),daysideoutwardmotiontoreconnection oncemore(6).Thesketchisschematicasthetailonthenightsideextends>100RE (RE =Earthradius) (Dungey,1965).

Figure1.5 Dawn–duskmeridianviewofopenmagnetospherewithpuresouthwardexternalfield.Thesolarwind flowisintothepage.Thesolarwindelectricfieldvoltage ΔΦ isprojecteddownthe(equipotential)fieldlinesofthe polarcaptothepolarionosphere.

interiorofthemagnetosphere.Fieldlinesandplasma moveasawholeasthefieldisfrozenintothemotion. TheexceptionisinthetwoplacesmarkedbyXwhere reconnectionoccurs.Herethefieldlinesbreakandreconnect.Numbersonthefigureoutlinehowasinglefieldline evolvesinasteadyconfigurationwithreconnectionoccurringonthedayside(2),nightside(4)todaysidereconnectiononcemore(6).Plasmainflowtowardsthecenterof thetailfromeachtaillobeisbalancedbyacceleratedoutflowstowardstheEarthanddowntail.Theantisolarflow isonthefieldinthepolarcap.Theblackarrowsrepresent thesolarwindflow.Thedirectconnectionofthesolar windmagneticfieldtothepolarcapmagneticfieldiswhat causesthepolarcapantisolarflow.Atlowerlatitudesthe sunwardflowreturnsmagneticfluxtothedaysidereconnectionpoint.

Thedawn–duskelevationoftheDungeymodelis showninFigure1.5inthesimplestpurelysouthward externalfieldcase.Inthissketch,theelectricfieldconfigurationisillustrated.Inthesteadystatetheflowing plasmaandthesouthwardfieldinthesolarwindgiverise toaneastwardelectricfieldandapotentialdropalongthe neutrallinewherereconnectiontakesplace.Thatpotentialisprojectedintothepolarcapalongthefieldlines asindicatedinthesketch.

AfurthersketchisshowninFigure1.6,whichillustratestheresultingcurrentsystemintheionospheredue totheelectricpotentialimposedacrosstheionosphere

atthefeetofthefluxtubesintheionosphere.ThecontinuousarrowedthinlinesinFigure1.6representtheionosphereHallcurrent.Itisassumed,onceagainfor simplicity,thattheionospherehasauniformconductance.TheHallcurrentisinpreciselytheoppositesense tothedoublevortexflowsystemthatDungeyenvisaged wouldbeinducedbymomentumtransferfromthesolar windintheionosphere.TheHallcurrentisnondissipative.However,thereisalsoadissipativecurrent,thePedersencurrentinthedirectionoftheimposedelectricfield. ThePedersencurrentflowisindicatedbydashedarrowed lines.ItcanbeseenfromthearrowsthatthePedersencurrentchangessenseasonecrossesthelocationrepresented bythethickovalcurve.Onmagnetohydrodynamictime scales,electricalcurrentsaredivergence-free.Accordingly,thenetinfloworoutflowofhorizontalcurrentthat occursintheovalregionmeansthattherehastobecurrentflowalong(upordown)themagneticfieldhere. ThesearethecurrentspostulatedbyBirkeland(1908) andarecommonlycalledBirkelandcurrents.Localized magneticperturbationsweredirectlyobservedabove theauroralzonein1966(Zmudaetal.,1967)andlinked toBirkeland’soriginalproposalbyCummingsandDessler(1967).

ComparisonofFigures1.5and1.6showsthattheBirkelandcurrentsconnectthevoltageassociatedwiththe solarwindmotiontoanionosphericloadrepresented bythedissipativePedersenconductance.

Currents Pederen Hall Birkeland

Figure1.6 Sketchofthecurrentsinducedintheionosphereinthesimple(southwardIMF)openmagnetosphere. ThePedersencurrentsarediscontinuousattheovalcurve,whichcorrespondstotheauroralzone.Thefieldaligned Birkelandcurrentflowin/outatthediscontinuity.Thefieldlinespolewardoftheovalareopenandextendinto interplanetaryspace.Equatorwardthefieldlinesgofromnortherntosouthernhemisphereandsoareclosed. ComparingtheconfigurationsofFigures1.5and1.6showsthattheionosphereactsasaloadonthesolarwind.

MHDtreatstheelectricfieldparalleltothebackground fieldasnegligible,sotheBirkelandcurrentsmightseemto benondissipative.Thisisnotnecessarilyso.Theelectrons everywherewouldneedbeinfinitelymobile.Current (i.e.electrons)isdrawnalongthefieldsimplytoensure thatoverallcurrentsclose.Aslongasthereisareservoir ofcoldelectronssuchasintheionosphere,thiscanbe achievedwithverysmallvoltages.However,wherethe large-scalecurrentflowrequiresupwardcurrentand accordinglydownwardmotionofelectronsfroma magnetosphericsource,substantialvoltagesmaybe needed.Thebasiccalculationwassurprisinglylatein coming(Knight,1973).Theaccelerationofelectrons downintotheionosphereprovidesauroraandalsocan exciteradiowaves(auroralkilometricradiation) (Gurnett,1974).

1.9.PARTICLETRANSPORTINTHE OPENMODEL

In1963camethefirstdetectionoftheboundary ofthemagnetosphere,themagnetopause(Cahilland

Amazeen,1963).Dungey ’ ssketchinthe1961paper didnotshowasharpboundarybetweensolarandterrestrialregimesandtherewerethosewhosawthesharp boundarypredictedbyChapmanandFerraroasevidenceagainstanopenmodel,regardlessofthefactthat itwasclearthatsomeformofparticleentryhadtooccur. Ofcourse,theinterplanetaryfieldisrarelypurelysouthward.Thesimplesymmetryoftheinternalmagnetosphericcirculationintheopenmodeloutlinedin Figures1.3–1.6hereismodifiedandskewedbyaddition ofeastward,westwardorradialexternalfields(seee.g. Cowley1981a,1981b).OneshouldalsonotethatthediagraminFigure1.4isschematic.Itmaybetopologically correctbut,intruth,themagneticfieldisverydistended onthenightside,aregionknownasthegeomagnetictail withathinneutralsheetinthecenter.Nightsidereconnectiontakesplaceinthesheetandplasma,whichhas enteredbymovingalongthefieldinthepolarcap, maybeacceleratedthere.

ThefirstevidencethatDungey’smodelmagnetosphere wassoundcameinthemid-1960sfromexperimentalevidence(FairfieldandCahill,1966)thatgeomagneticactivityincreasedwithasouthwardinterplanetarymagnetic

V Dusk Sun Dawn

Ionospheric surface

fieldcomponent.However,thereconnectionmodelwas slowingainingwideacceptance.

Theopenmagnetosphereprovidedastraightforward explanationfornotonlyentryofplasmafromthesolar environmentbutalsoforaccelerationandheating.Ina steady-statepictureofacirculationofplasmawehave alreadydescribed,theplasmacontainedontheclosedflux tubesmovingtowardstheEarthfromthetailencounters fluxtubesofdecreasingvolume.Asaresult,itisheated adiabaticallyi.e.becauseitisisolatedthermally,itsaccessiblephasespacevolumeisconstant;decreasingphysical volumemeansincreasedthermalmotion.Theinward motionisthedriveninterchangemotionreferredtoearlier andtheadiabaticprocesswasdescribedbyGold(1959). Gold’senvisagedmotionwasoutwardandspontaneous. Thefactthattheinwardmovingplasmaisheatedisthe reasonthatthemotionmustbedrivenwithenergyultimatelycomingfromthesolarwind.Becausethemotion oftheplasmaiscollision-free,theenergygainasparticles aremovedtowardstheEarthispitchangledependent. Twoadiabaticinvariants,themagneticmomentandlongitudinalinvariantdescribethemotiontransversetothe fieldandalongthefieldrespectively.Thelongitudinal invariantgovernsplasmamotionalongthefield.The invariantappearsmisnamedinamagnetosphericcontext, asthecorrespondingparticlemotionisthebouncemotion betweenmagneticmirrorsbackandforthinlatitudealong themagneticfield.Itwasoriginallyderivedinthecontrollednuclearfusionprogram,wherethecorresponding motionwasalongthedevice.Detailedanalysisoftheadiabaticmotionwiththetwoinvariantsmentionedaswell asathird,thefluxinvariantassociatedwithdriftaround theEarth,wasworkedoutinthe1950s.AnexcellenttheoreticaloverviewisgivenbyNorthropandTeller(1960). Nakadaetal.(1965)organizedspacecraftenergeticparticledatatoderivethephasespacedistributionusingthe firsttwoinvariantsandshowedexplicitlythatthesource wasexternal.

Eachinvarianthasanassociatedperiodicmotion.In practice,solarwindmagnetospherecouplingisnot steady.Themagnetosphericcirculationproceedsinfits andstarts,mostlyontimescalesshortcomparedwith thetimechargedparticlestaketomovearoundtheEarth. Thismeansthattheinjectionofparticlesfromthetailin theclosedfieldregiontakesplaceinasporadicmanner. Asaresult,withintheclosedfieldregionthemotionof manyoftheenergeticparticlesthatmakeuptheringcurrentandtheradiationbeltsisbestdescribedasadiffusion. Particleradialmotionisarandomwalkasparticlesmove inoroutaccordingtowheretheyareintheirdriftphaseas solarterrestrialcouplingvaries.Anearlycomprehensive studyisgiveninSchulzandLanzerotti(1974).

Ifthefieldvariesonatimeorspacescalecomparable withtheLarmorgyrationthemomentinvariantis

violatedand,similarly,variationonthebouncetimescale willchangethelongitudinalinvariant.Itfollowsthat plasmawavesatfrequenciesneartheelectronoriongyrofrequencycanmodifythemagneticmomentandproduce scatteringinpitchangle.Withasmallenoughpitchangle, energeticchargedparticlesarelostastheirmirrorpoints becomeoflowenoughaltitudethattheycollidewith atmosphericneutrals.Anearlyanalysisofthecoupling betweenpitchanglescatteringandbackgroundwave instabilitywasdonebyKennelandPetschek(1966), whousedtheapproachtoderivealimitonstablytrapped particlefluxthatfittedwellwithenergeticparticledata fromtheearlyExplorer12and14spacecraft.

Inpractice,thesolarterrestrialinteractionoccurson severaltimescales.Asolarwindpressureincreasewill produceanincreaseintheEarth’sfieldworldwide,known asastormsuddencommencementinminutes.Subsequently,changesinthedirectionoftheinterplanetary fieldwillproduceaseriesofburstsofmagnetospherewide flowdrivenbythesolarwindfromthepolarcap,as describedintheprevioussection.Thesearealsothefits andstartsreferredtoabove.AkasofuandChapman (1961)introducedthetermsubstormtodescribethis. Theypointedoutthatthephenomenonwhosetimescale istypicallyaroundtwohourshadoriginallybeenidentifiedbyBirkeland(1908)asapolarelementarystorm. Plasmainjectionandheatingoccurwitheachsubstorm, eventuallybuildinguparingcurrentaroundEarthover adayortwo.Theringcurrentcarriedbytheinjectedparticlesprovidesthegeomagneticfielddepressionwhich characterizesthestormmainphase.

1.10.CONCLUDINGREMARKS

Byaround1970orso,notonlyhadthebasicgeography ofthemagnetospherebeenestablishedbutalsoalotofthe groundworkhadbeendoneforunderstandinghowit worked.However,anhonesthistoryneedstonotethat therewasstillalargedegreeofcontroversy.Indeed,much ofthiswasechoingtheScandinavian–Anglo-Saxon schismofthe1940sand1950s.Itwasnotgenerallyseen thatDungey’sopenmagnetospheremodelbroughtcriticalaspectsofbothmodelstogether.Forinstance,afinal importantmorphologicaldiscoveryin1971wasofmagnetosheathplasmapenetratingdeepintheterrestrialfield, thepolarcusp(HeikkilaandWinningham,1971;Frank, 1971).Despitetheknownpresenceofanexternalfield, manyimmediatelyidentifiedtheresultwiththelikely entryofplasmathroughtheChapman–Ferraroneutral points(markedQinFigure1.2).Moreover,anearly paperbyRusselletal.(1971)evencontainedthetantalizinginformationthatthecuspappearedtomoveupor downinlatitudeastheexternalfieldturnednorthward orsouthward.Nevertheless,thepapermadenoreference

totheDungeymodel.Similarly,inthepreviousyeara paperbyAubryetal.(1970)hadshownthemagnetopause erodingatlowlatitudesinthepresenceofasouthward externalfieldbutalsomentionedneitherDungeynor reconnection.Reconnectionhadbecomeacontroversial terminmagnetosphericphysicsatthistime (Southwood,2015).ThefinaldenouementoftheDungey openreconnectionmodelofthemagnetospherehadto awaitthedirecthighresolutionobservationsofheating andplasmaaccelerationinthemagnetopauseinconditionspreciselyconsistentwithreconnectionbytheISEE (InternationalSunEarthExplorer)1and2spacecraft (Paschmannetal.,1979).

ACKNOWLEDGMENTS

WorkatImperialCollegewassupportedbyUKSTFC GrantsST/K001051/1andST/N000692/1.

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