Solar Dynamics and Magnetism from the Interior to the Atmosphere PDF
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Solar Dynamics and Magnetism from the Interior to the Atmosphere Nagi N. Mansour (cid:2) Alexander G. Kosovichev (cid:2) Rudolf Komm (cid:2) Dana Longcope Editors Solar Dynamics and Magnetism from the Interior to the Atmosphere Previously published in Solar Physics Volume 287, Issues 1–2, 2013 Editors NagiN.Mansour RudolfKomm NASAAmesResearchCenter NationalSolarObservatory MoffettField,CA,USA Tucson,AZ,USA AlexanderG.Kosovichev DanaLongcope StanfordUniversity MontanaStateUniversity Stanford,CA,USA Bozeman,MT,USA ISBN978-1-4899-8004-5 ISBN978-1-4899-8005-2(eBook) DOI10.1007/978-1-4899-8005-2 SpringerNewYorkHeidelbergDordrechtLondon LibraryofCongressControlNumber:2013953962 ©SpringerScience+BusinessMediaNewYork2014 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpartofthe materialisconcerned,specificallytherightsoftranslation,reprinting,reuseofillustrations,recitation,broad- casting,reproductiononmicrofilmsorinanyotherphysicalway,andtransmissionorinformationstorage andretrieval,electronicadaptation,computersoftware,orbysimilarordissimilarmethodologynowknown orhereafterdeveloped.Exemptedfromthislegalreservationarebriefexcerptsinconnectionwithreviews orscholarlyanalysisormaterialsuppliedspecificallyforthepurposeofbeingenteredandexecutedona computersystem,forexclusiveusebythepurchaserofthework.Duplicationofthispublicationorparts thereofispermittedonlyundertheprovisionsoftheCopyrightLawofthePublisher’slocation,initscur- rentversion,andpermissionforusemustalwaysbeobtainedfromSpringer.Permissionsforusemaybe obtainedthroughRightsLinkattheCopyrightClearanceCenter.Violationsareliabletoprosecutionunder therespectiveCopyrightLaw. Theuseofgeneraldescriptivenames,registerednames,trademarks,servicemarks,etc.inthispublication doesnotimply,evenintheabsenceofaspecificstatement,thatsuchnamesareexemptfromtherelevant protectivelawsandregulationsandthereforefreeforgeneraluse. Whiletheadviceandinformationinthisbookarebelievedtobetrueandaccurateatthedateofpublication, neitherthe authors nor theeditors nor the publisher canacceptanylegalresponsibility for anyerrors or omissionsthatmaybemade.Thepublishermakesnowarranty,expressorimplied,withrespecttothematerial containedherein. Coverillustration:NASA Printedonacid-freepaper SpringerispartofSpringerScience+BusinessMedia(www.springer.com) Contents Preface (cid:3) (cid:3) (cid:3) (cid:3) N.N.Mansour A.G.Kosovichev R.Komm D.Longcope J.W.Leibacher 1 LOCALANDGLOBALHELIOSEISMOLOGY WhatHaveWeLearnedfromHelioseismology,WhatHaveWeReallyLearned, andWhatDoWeAspiretoLearn? D.Gough 9 TheDynamicsoftheSolarRadiativeZone (cid:3) A.Eff-Darwich S.G.Korzennik 43 LatestResultsFoundwithRing-DiagramAnalysis (cid:3) (cid:3) (cid:3) (cid:3) (cid:3) (cid:3) C.S.Baldner S.Basu R.S.Bogart O.Burtseva I.GonzálezHernández D.Haber (cid:3) (cid:3) (cid:3) (cid:3) (cid:3) F.Hill R.Howe K.Jain R.W.Komm M.C.Rabello-Soares S.Tripathy 57 SubsurfaceSupergranularVerticalFlowsasMeasuredUsingLargeDistance SeparationsinTime–DistanceHelioseismology (cid:3) T.L.DuvallJr. S.M.Hanasoge 71 SubsurfaceMeridionalFlowfromHMIUsingtheRing-DiagramPipeline (cid:3) (cid:3) (cid:3) (cid:3) (cid:3) R.Komm I.GonzálezHernández F.Hill R.Bogart M.C.Rabello-Soares D.Haber 85 PropertiesofHigh-FrequencyWavePowerHalosAroundActiveRegions: AnAnalysisofMulti-heightDatafromHMIandAIAOnboardSDO (cid:3) (cid:3) (cid:3) (cid:3) S.P.Rajaguru S.Couvidat X.Sun K.Hayashi H.Schunker 107 Global-OscillationEigenfunctionMeasurementsofSolarMeridionalFlow (cid:3) (cid:3) (cid:3) M.Woodard J.Schou A.C.Birch T.P.Larson 129 AnalysisoftheHelioseismicPower-SpectrumDiagramofaSunspot (cid:3) J.Zhao D.-Y.Chou 149 SOURCESOFSOLARSHAPEANDIRRADIANCEVARIATIONS RevisitingtheSolarOblateness:IsRelevantAstrophysicsPossible? (cid:3) J.P.Rozelot Z.Fazel 161 VariabilityofSolarFive-MinuteOscillationsintheCoronaasObserved bytheExtremeUltravioletSpectrophotometer(ESP)ontheSolarDynamics Observatory/ExtremeUltravioletVariabilityExperiment(SDO/EVE) (cid:3) (cid:3) (cid:3) (cid:3) L.Didkovsky A.Kosovichev D.Judge S.Wieman T.Woods 171 LARGE-SCALEDYNAMICS,MAGNETISM,ANDDYNAMO SolarDynamoandToroidalFieldInstabilities A.Bonanno 185 AComparisonofSolarCycleVariationsintheEquatorialRotationRatesoftheSun’s Subsurface,Surface,Corona,andSunspotGroups J.Javaraiah 197 RecoveringJoy’sLawasaFunctionofSolarCycle,Hemisphere,andLongitude (cid:3) B.H.McClintock A.A.Norton 215 EMERGINGMAGNETICFLUXANDSUBSURFACEDYNAMICS ASearchforHelioseismicSignatureofEmergingActiveRegions S.Kholikov 229 ComparingSimulationsofRisingFluxTubesThroughtheSolarConvectionZone withObservationsofSolarActiveRegions:ConstrainingtheDynamoFieldStrength (cid:3) (cid:3) M.A.Weber Y.Fan M.S.Miesch 239 FORMATION,STRUCTURE,ANDEVOLUTIONOFSUNSPOTSANDACTIVEREGIONS TheSub-surfaceStructureofaLargeSampleofActiveRegions (cid:3) (cid:3) C.S.Baldner R.S.Bogart S.Basu 265 HorizontalFlowsinthePhotosphereandSubphotosphereofTwoActiveRegions (cid:3) (cid:3) Y.Liu J.Zhao P.W.Schuck 279 ActiveRegionFormationthroughtheNegativeEffectiveMagneticPressureInstability (cid:3) (cid:3) (cid:3) (cid:3) K.Kemel A.Brandenburg N.Kleeorin D.Mitra I.Rogachevskii 293 MAGNETICTOPOLOGYANDDYNAMICSOFTHESOLARATMOSPHERE InfraredObservationsfromtheNewSolarTelescopeatBigBear (cid:3) P.R.Goode W.Cao 315 ANonlinearForce-FreeMagneticFieldApproximationSuitableforFast Forward-FittingtoCoronalLoops.I.Theory M.J.Aschwanden 323 ANonlinearForce-FreeMagneticFieldApproximationSuitableforFast Forward-FittingtoCoronalLoops.II.NumericCodeandTests (cid:3) M.J.Aschwanden A.Malanushenko 345 ANonlinearForce-FreeMagneticFieldApproximationSuitableforFast Forward-FittingtoCoronalLoops.III.TheFreeEnergy M.J.Aschwanden 369 OriginsofRolling,Twisting,andNon-radialPropagationofEruptiveSolarEvents (cid:3) (cid:3) (cid:3) O.Panasenco S.F.Martin M.Velli A.Vourlidas 391 ASpatio-temporalDescriptionoftheAbruptChangesinthePhotosphericMagnetic andLorentz-ForceVectorsDuringthe15February2011X2.2Flare G.J.D.Petrie 415 TheWave–DriverSystemoftheOff-DiskCoronalWaveof17January2010 (cid:3) (cid:3) M.Temmer B.Vrsnak A.M.Veronig 441 DOI10.1007/978-1-4899-8005-2_1 ReprintedfromSolarPhysicsJournal,DOI10.1007/s11207-013-0377-6 SOLAR DYNAMICS AND MAGNETISM Preface NagiN.Mansour·AlexanderG.Kosovichev· RudolfKomm·DanaLongcope·JohnW.Leibacher Publishedonline:27August2013 ©Springer2013 ThisvolumecontainsacollectionofarticlesonthetopicofSolarDynamicsandMagnetism fromtheInteriortotheAtmospherestimulatedbytheLWS/SDO-3/SOHO-26/GONG-2011 workshopofthesamename,whichwasheld31October–4November2011,atStanford, California,USA. Thegoaloftheworkshopwastodiscussrecentadvancesandnewproblemsintheexplo- rationoftheSun’sinteriorstructure,solardynamicsanddynamo,mechanismsofsunspot andactiveregionsformation,sourcesofsolarirradiancevariations,linksbetweenthesub- surface dynamics, and flaring and CME activity. NASA’s Solar Dynamics Observatory SolarDynamicsandMagnetismfromtheInteriortotheAtmosphere GuestEditors:R.Komm,A.Kosovichev,D.Longcope,andN.Mansour N.N.Mansour(B) NASAAmesResearchCenter,NASAAdvancedSupercomputingDivision,MoffettField,CA,USA e-mail:[email protected] A.G.Kosovichev StanfordUniversity,Stanford,CA,USA e-mail:[email protected] R.Komm·J.W.Leibacher NationalSolarObservatory,Tucson,AZ,USA R.Komm e-mail:[email protected] J.W.Leibacher e-mail:[email protected] D.Longcope MontanaStateUniversity,Bozeman,MT,USA e-mail:[email protected] J.W.Leibacher Institutd’AstrophysiqueSpatial,Orsay,France 1 Reprintedfromthejournal N.N.Mansouretal. (SDO)missionhasbeenprovidingalargeamountofnewdataonsolardynamicsandmag- neticactivitiesduringtherisingphaseofthehighlyunusualSolarCycle24.Thesedataare complementedbytheSolarandHeliosphericObservatory(SOHO)missionandbyground- basedobservatories,whichincludetheGlobalOscillationNetworkGroup(GONG)helio- seismologynetworkandtheNewSolarTelescope(NST).Inaddition,theseobservationsare supported by realistic numerical simulations on high-end computers. This unprecedented amount of data provides a unique opportunity for multi-instrument investigations that ad- dress fundamental problems of the origin of solar magnetic activity at various spatial and temporalscales.Thedataarebeingusedtodevelopnewmethodsforforecastingsolarcy- cles,emergenceandevolutionofactiveregions,andtheirflaringandCMEactivity. Thisvolumerepresentsanattempttodevelopasynergyamonginvestigationsofthesolar interior by helioseismology, surface magnetism, and the atmospheric dynamics, by using bothstate-of-the-artobservationsandnumericalsimulations.Thearticlesareorganizedin sixchapters: i) LocalandGlobalHelioseismology. ii) SourcesofSolarShapeandIrradianceVariations. iii) Large-ScaleDynamics,Magnetism,andDynamo. iv) EmergingMagneticFluxandSubsurfaceDynamics. v) Formation,Structure,andEvolutionofSunspotsandActiveRegions. vi) MagneticTopologyandDynamicsoftheSolarAtmosphere. Somearticlesfitinmorethanonetopic,andinsuchcasestheclassificationisnotwell- defined,andwerecommendthatreadersconsultthewholetableofcontents.Someofthe articlesarewrittenasInvitedReviews,butallcontainnewresultsandideasthatreflectthe currentstatusofthefield,newchallenges,andfutureperspectives. Inrecentyears,ourunderstandingofthesolarinteriorhasadvancedsubstantiallythanks tothedevelopmentofhelioseismologytechniquesandcontinuousobservationsofsolaros- cillations by the Helioseismic and Magnetic Imager (HMI) onboard SDO and by GONG. High-precision measurements of oscillation frequencies have provided the radial sound- speed profile and the distribution of the angular velocity through the whole interior, ex- ceptperhapstheveryinnercoreoftheSun.Thesemeasurementsprovidedatestofstellar- evolutiontheoryandthestandardsolarmodel.However,thediscrepancybetweentheabun- dance of heavy elements determined spectroscopically on the solar surface and the abun- dancededucedfromsolarmodelingandglobalhelioseismologydataprovidesastrongin- dicationthatourunderstandingofthebasicphysicsofthesolarinteriorisstillincomplete. Inparticular,therearefundamentalissuesrelatedtomodelingofnon-idealpropertiesofthe solar plasma, and the equation of state, which directly affect the accuracy of the estimate fortheheavyelementabundancebyhelioseismology.Inaddition,thereareindirecteffects duetotheuncertaintyofthesolarageandmagnetic-fieldeffects.Therefore,itisimportant todevelopasynergyofmoreaccuratefrequencyinversionmethodsanddetaileddescription ofthemicro-physicsinordertoresolvetheheavyelementabundanceproblem.Also,itbe- comesincreasinglyimportanttoinvestigatetheglobaldynamicsoftheSun.Inadditionto thetraditionalmethodsofglobalhelioseismology,basedoninversionofrotationalfrequency splitting,newmethodsoflocalhelioseismology,whichmeasurethemeridionalcirculation andlarge-scaleflowsinthequiet-Sunandactiveregions,arebeingactivelydeveloped.In particular,theverylongtimeseriesofsolaroscillationsobservedbytheMichelsonDoppler ImageronboardtheSOHOspacecraftandGONGduringthewholesolarcyclefrom1995– 2008,providednewmeasurementsofthesolardifferentialrotationdownto0.2solarradii. However, while the results of these measurements are consistent with the hypothesis of a Reprintedfromthejournal 2 Preface uniformlyrotatingcore,theycannotruleoutthattheenergy-generatingcorerotatesfaster orslowerthantheouterradiativezone.Thisisalsoaproblemoffundamentalimportance forunderstandingtheformationandevolutionoftheSun. Local helioseismology based on measurements and inversion of frequency shifts and acoustictraveltimesiscapableofprovidingthe3Dstructureanddynamicsoftheconvection zone.Theinterpretationofthesemeasurementsandinversionsisasubjectofhotdebate.The debatehasbeensubstantiallyimprovedwiththedevelopmentofrealisticnumericalsimula- tionsofrandomlyexcitedacousticwavesin3DmodelsoftheSunthatincludebackground flowsandmagneticfields.Theapproach basedonasynergyofatime–distance helioseis- mologymethodandnumericalsimulationsprovidednewestimatesofthesubsurfaceflow structure of supergranulation, which led to a surprising result that strong upflows may be hidden 2 Mm beneath the surface supergranulation pattern dominated by outflows. In ad- dition, local-helioseismology measurements based on unique multi-wavelength data from SDOprovidenewknowledgeaboutwavepropagationinmagneticregionsofthesolarat- mosphere,andwavetransformationandscattering.Thesenewresultschallengetheexisting simplemodelsofMHDwavepropagationandpointtotheneedforfurtherdevelopmentof numericalsimulationsofwavesinrealisticconditionsofturbulentandradiatingplasmaof magnetic regions. It becomes more and more clear that MHD waves excited by turbulent convectionplayafundamentalroleinthedynamicsandenergeticsofthesolaratmosphere. Variationsofthesolardiameter,shape,andirradianceareofparticularinterestbecause ofthelongandrichhistoryoftheseinvestigations,theirroleinsolarevolution,andglobal changesoftheEarth’sradiationandspaceenvironment.Thehigh-precisionmeasurements onboard SDO open new perspectives for improving our knowledge of solar variability on widetemporalandspatialscales,andadvancingourunderstandingoftheunderlyingphys- ical mechanisms. In particular, these measurements encourage revisiting of old questions about solar oblateness, the relationship between oblateness changes and solar cycles, the constraintsonrelativisticcelestialmechanicsandalternativetheoriesofgravitation.Atthe high-frequency end of the irradiance spectrum, accurate measurements from the Extreme Ultraviolet Variability Experiment (EVE) onboard SDO led to the detection of the global five-minuteoscillationsinthecorona,andtheirmodalstructure,whichcorrespondstothe globalmodesobservedinthephotosphere.Ifthissurprisinglinkbetweentheinteriorand coronaisconfirmedbyfurtherobservations,itwillhaveimportantimplicationsontheories ofwavepropagationontheSunandmechanismsofcoronalheating. Helioseismologyprovidescriticalinformationfordevelopingdynamomodelsoftheso- lar magnetic cycle. After the discovery of the tachocline, a narrow rotational-shear layer atthebottomoftheconvectionzone,dynamotheoriesassumedthatthetoroidalmagnetic fields, which are the primary source of sunspot regions, are generated and stored in the tachocline.Inordertoexplainthesunspot“butterfly”diagram,thesetheoriesassumedthat theinternalmeridionalcirculationtransportsthetoroidalfieldinthetachoclinetowardsthe Equator in the courseof the solar cycle, and that this toroidal field emerges locally in the formofcompact(cid:2)-shapedmagneticloopsandformssunspotregions.However,thereare serious,unsatisfactoryaspectsofsuchanadvection-dominateddynamobecausethestrength ofthereturnmeridionalflowislargelyunknown,andbecausetherequirededdydiffusivity isaboutoneorderofmagnitudegreaterthanispredictedbystandardmixing-lengththeory. Onepossiblealternativetothe“flux-transport”theoryisadynamomodelthattakesintoac- counteffectsofthenear-surfacerotational-shearlayer,alsodiscoveredbyhelioseismology. In the new theory, the magnetic field is generated in the bulk of the convection zone and formsthebutterflypatterninthesubsurface-shearlayer.Thistheoryrepresentsaparadigm shiftinourunderstandingofthesolardynamoandcycles,andrequiresfurtherdetailedin- vestigation.Itisquiteintriguingthatafterthisworkshopnewlocal-helioseismologyresults 3 Reprintedfromthejournal N.N.Mansouretal. providedevidencethatthemeridionalcirculationmayconsistoftworadialcells,makingthe flux-transporttheoryevenmoreproblematic.Ultimately,theissuewillberesolvedbyim- provingtheaccuracyofthehelioseismologymeasurements,andnewapproachesarebeing activelydeveloped.Inaddition,importantinformationisprovidedfromsynopticanalysisof magneticpatternsonthesolarsurfacesuchasrotationofsunspotgroups,andtheirinclina- tionrelativetotheEquator(Joy’slaw).Futuredynamotheorieswillhavetoexplainthese patterns. Observations and modeling of the emergence of the dynamo-generated magnetic flux areofprimaryimportanceinheliophysicsfortwomainreasons:First,theemergingfluxis directly linked to the dynamo process and carries information about the dynamo; second, theemergingfluxcantriggerflaresandCMEs,andthusisimportantforforecastingspace weather and solar storms. Helioseismology made a substantial breakthrough in this topic by detecting acoustic travel-time variations associated with the emerging flux in the deep convectionzone(atadepthof45–70Mm)24–48hoursbeforethemagneticfieldbecomes visibleonthesurface.Thenatureofthetravel-timevariationsisnotyetunderstood.These areprobablyrelatedtoscatteringofacousticwavesontheemergingfluxinhomogeneities. Solvingthisproblemrequiresmodelingofthefluxemergenceinrealisticturbulentcondi- tionsoftheconvectionzone.Simulationsarebeingactivelydeveloped,andusedforunder- standinglinksbetweenthedynamocharacteristicsandpropertiesoftheemergingflux. Afteremergenceatthesurface,themagneticfluxisamixtureofsmallelementsofop- positepolarity.However,veryquickly,elementsofeachpolaritymergeandformcompact andstablesunspotstructures.Aftertheformation,thesunspotmagneticfieldscontinueto evolve, interact with magnetic fields of the opposite polarity, and form unstable magnetic configurationsresultinginplasmaeruptions.Itseemsthatthemagnetic-fielddynamicsob- served on the surface is controlled by subsurface flows. Interaction of these flows, driven bytheconvective-energyflux,withmagneticfieldsisakeytounderstandingthesolarac- tivity,butthephysicsofthisinteractionisextremelycomplicated.Currently,onlythefirst stepsarebeingmadebylocal time–distance helioseismologytomap thesub-surfaceflow patternsandlinkthesetothesurfacemagneticfielddynamics.NewresultsfromtheHMI instrumentonboardSDO,obtainedforashallow500kmdeepregion,whichwaspreviously inaccessibleduetolowspatialresolutionofpreviousinstruments,revealconvergingplasma flowsinthesunspotumbraarea,surroundedbydivergingflows.Thesemeasurements,sup- ported by results of correlation tracking of the surface field, represent a significant chal- lengeforsomerecentMHDsimulationsofsunspots,whichpredictedonlydivergingflow patterns. Another local-helioseismology technique, ring-diagram analysis, shows that the subsurfacestructureofsunspotsischaracterizedbyashallowlayerofreducedwavespeed andadeeperlayerofhighersoundspeed.Qualitatively,thisisconsistentwiththeprevious time–distancehelioseismologyresults.However,thedepthestimatesoftheselayersaresig- nificantly different. This difference may be related to differences in the spatial resolution, butultimatelywillberesolvedwhenlarge-scalerealisticMHDsimulationsofsunspotswill become available. So far, only relatively small, pore-like structures were modeled in the simulations self-consistently without specifying artificial boundary conditions to prevent thestructure’sdecay.Intheseself-consistentsimulations,themagneticstructuresaremain- tainedbyconvergingdowndraftsdrivenbysurfacecooling.Analternativemodelsuggests thatsunspot-likestructurecanformbecauseofthesuppressionofturbulentpressurebythe magnetic field. This suppression called “negative effective magnetic pressure instability” alsoresultsinconvergingdowndrafts.Inaddition,theinstabilityleadstoaredistributionof turbulentintensityandgaspressurethatcouldprovidedirectobservationalsignatures. The structure and dynamics of the atmosphere and corona is governed by magnetic fields generated by a dynamo in the deep convection zone and emerging on the solar Reprintedfromthejournal 4
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