Table Of ContentSolar 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
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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
