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A&A661,A107(2022)
/0004-6361/202040091Astronomy
cESO2022&
Astrophysics
SolarH excessduringSolarCycle24fromfull-diskflltergrams
oftheChromosphericTelescope
,2,3,,4,5,,äger1,-Gómez1,
,2,
1Leibniz-InstitutfürAstrophysikPotsdam(AIP),AnderSternwarte16,14482Potsdam,Germany
2UniversitätPotsdam,InstitutfürPhysikundAstronomie,Karl-Liebknecht-Straße24/25,14476Potsdam,Germany
3NationalSolarObservatory(NSO),3665DiscoveryDrive,Boulder,CO,USA80303
e-mail:******@
4InstitutodeAstrofísicadeCanarias(IAC),VíaLácteas/n,38205LaLaguna,Tenerife,Spain
5DepartamentodeAstrofísica,UniversidaddeLaLaguna,38205LaLaguna,Tenerife,Spain
6LaboratoryforAtmosphericandSpacePhysics,UniversityofColoradoBoulder,Boulder,CO80303,USA
Received8December2020/Accepted17February2022
ABSTRACT
,this
,othertracers,suchasCaiiK,aretypicallyusedto
,theSunisobservedconstantlyinH withgloballydistributedground-basedfull-diskimagers.
excessanddeflcitastracersofsolaractivityandcomparethemtoother
,weinvestigatewhethertheactiveregioncoveragefractionorthechangingH excessintheactive
regionsdominatestemporalvariabilityinsolarH observations.
-diskH flltergramsoftheChromosphericTelescopeandmorphologicalimageprocessing
techniquestoextracttheimagingH excessanddeflcit,whichwerederivedfromtheintensitiesaboveorbelow10%ofthemedian
intensityintheflltergrams,(plageregions)anddarkabsorption
features(fllamentsandsunspots).Inaddition,thethresholdswereusedtocalculatethemeanintensityIE=DforH excessanddeflcit
mean
excessanddeflcitduringSolarCycle24andcompareittothemeanintensityandother
wellestablishedtracers:therelativesunspotnumber,,,wetriedtodetermine
howconstanttheH excessandnumberdensityofH
pixelsaboveorbelowtheintensitythresholdswereusedtocalculatetheareacoveragefractionofH excessanddeflcitregionson
theSun,whichwascomparedtotheimagingH excessanddeflcitandtherespectivemeanintensitiesaveragedforthelengthofone
,wepresenttheH excessandmeanintensityvariationofselectedactiveregionsduringtheirdisk
passageincomparisontothenumberofpixelsofH excessregions.
solarmaximum,wherebythepeakoftheH ,thecorrelationofthemonthly
averagesoftheH excessanddeflcitishighwithaSpearmancorrelationof=0: excessiscloselycorrelatedtothe
,
,,theH deflcitreflectsthecyclicbehavior
forH
similar,butwithdi ,wefoundthattheareacoveragefractionofH excessregionsandtheH excess
excessandthemeanintensity
ofH excessregionsisingeneral
relativelylow(=0:45)
fractionandmeanintensityleavesuspessimisticthatthedegeneracybetweenthesetwoquantitiescanbebrokenforthemodelingof
unresolvedstellarsurfaces.
:observational–Sun:chromosphere–Sun:activity–Sun:faculae,plages–Sun:fllaments,prominences–
stars:atmospheres
örer(.,Spörer1879;).-
lishedtherelativesunspotnumber,countingthespotgroupsand
Theflrstrecordofavaryingsunspotnumberthroughoutasolarindividualsunspots(Hathaway2010).Thismethodisstillused
-
Schwabeinthe19thcentury(Schwabe1844;Hathaway2010;videdbytheSolarInfluencesDataAnalysisCenter(SIDC)of
;Arlt&Vaquero2020).ThiswasfollowedintheRoyalObservatoryofBelgium,whichisusedtomonitorthe
(Carrington1858)and11-yearactivitycycleoftheSun.
ArticlepublishedbyEDPSciences
A107,page1of14:.
A&A661,A107(2022)
Inadditiontowhite-lightobservationsoftheSun,thesolaringAssembly(AIA,)onboardtheSolar
activitywasmonitoredindi erentwavelengths,forexample,theDynamicsObservatory(SDO,)aswellas
chromosphericCaiiKline,whoseemissioninplageregionsisdataoftheHinodeX-RayTelescope(XRT,).
correlatedtothemagneticfleldwithapower-lawrelationwithanThecontinuumobservationsshowedthatthelightcurvesof
(;;theactiveregion’sintensitydecreasewhenitisatdiskcenter,
).Livingstonetal.(2007)summarizedthewhilethelightcurveincreaseswhentheactiveregionisclose
resultsfromthreesolarcycleswherespectroscopicdataofdif- ectiswellknownfromobservationsofthe
(TSI,Fröhlich2012)andshowsthatthe
indexshowedthehighestvariationsthroughoutthecyclewithe ectsoftheumbraandpenumbraoftheactiveregiondominates
amplitudesofabout25%.-of-sightmagneticfluxaswellas
duetothesteepPlanckfunctionand,therefore,strongertem-theUVirradiance(1600Åand1700Å)showabell-shaped(or
peratureresponseatshortwavelengthsaround4000Å(Ayresmountain-shaped),UV
1989;Sheminova2012).Otherchromosphericlineindicators,wavelengthsaremoresensitivetofaculaeregionsratherthanto
includingtheHei10830Åequivalentwidth,Caii8542Åcen-sunspots(Simõ;).
traldepth,H centraldepth,orCNbandheadat3883Å,allDuringthesolarcycle,so-calledactivelongitudesareestab-
showedvariationswiththesolarcycle,butwithalowerrela-,wheresunspots
tiveamplitudeascomparedtoCaiiK(;predominantlyform(Berdyugina&Usoskin2003;Hathaway
).Full-diskCaiiKmeasurementsshowan2010;Kramynin&Mikhalina2021).Theycanbestudiedby
averageincreaseof30%ofthecentralintensitybetweenmin-creatingCarringtonreferenceframesforeachsolarrotation.
imumandmaximumofthesolarcycle(White&LivingstonBerdyugina&Usoskin(2003)discoveredthattheactivelongi-
1981),
about180.Thelocationoftheactivelongitudechangesbetween
White&Livingston(1981)suggestedthatthevariabilityofthe
quiet-Sunnetworkisnegligibleintherisingphaseofthesolarsolarcycles,butitcanbeapersistentstructureforuptotwo
.(2016)inspectsthedecades(Hathaway2010).
correlationoftheCaiiKemissionindexandthesunspotnum-TheSunisregularlyobservedinanotherprominentchro-
,thatistosaytheH spectrallineat
oryears,whichtheyexplainbythehighcorrelationofboth6562:8Å.SeveralobservatoriesformtheGlobalH Network
.(2010)usedaver-(),includingtheBBSOandKanzelhöhe
agefull-diskimagesoftheBigBearSolarObservatory(BBSO,SolarObservatory(KSO,Otruba1999),whichtakeregular
)tocalculateanindexusinganadaptiveinten-full-diskimagesinthelinecoreofH .Intotal,sevenfacili-
sitythresholdtoextractthebrightplageregionsfromCaiiKtiesaroundtheworldarepartofthisnetwork,whichcontin-
full- line-,theGlobal
inJohannessonetal.(1998).Withthisindex,theycharacter-OscillationNetworkGroup(GONG,)ofthe
izedthesolaractivityofSolarCycle23fordi erentthresh-(NSO)consistsofsixfacil-
,whichproduce,amongotherdataproducts,timeseries
datacollectionofCaiiKobservationswasrecentlypresentedinoffull-diskH
Chatzistergosetal.(2020),whocollectedaround290000full-addition,otherobservatoriesprovideregularfull-diskH obser-
diskCaiiKobservationsfrom43datasetsincludingobserva-vations,forexample,theSolarFlareTelescopeinMitaka,Japan
(Hanaoka&Sakurai2020)andtheChromosphericTelescopein
,Spain(ChroTel,;Bethgeetal.
Otherwell-establishedsolarindicesincludeMgiiandthe2011).Thelargenumberofground-basedfacilitiesallaround
ÅÅhasbeenusedsince1978asaproxyforfull-diskH flltergrams,bridgingbadweatherlocallyandthe
solaractivity(Viereck&Puga1999).Theindexiscalculatedday-nightcycle.
fromthecore-to- throughoutthesolarcycleis
Mgiiindexvariesupto20%-integratedobservations(Livingstonetal.
Itisespeciallygoodinmonitoringsolarfaculae,;).TheH linehastheadvantageof
(1997)determinedfromsolarirradiancemodels,whichconsiderdisplayingfllamentsalongsidesunspotsasdarkabsorptionfea-
-
erenttootherchromosphericactivityindicators
(Tapping&Charrois1994;suchasHei10830Å,whereplageandfllamentsarebothseen
Hathaway2010).Severalmeasurementsadayareobtained,-
observationswasdiscussedinMeunier&Delfosse
correlatedwiththerelativesunspotnumber,butwithalagtime(2009).TheyfoundahighercorrelationbetweentheCaiiK
ofaboutonemonth(Hathaway2010).indexandtheH integratedfluxduringtheascendingphaseof
Singleactiveregionscaninfluencethetotalsolarirradi-thecyclecomparedtotheminimum,whichtheyexplainedisdue
.
hoursforsmallephemeralregionstomonthsforlargeactiveFilamentsarethedominatingabsorptionfeaturesonthesolar
regions(vanDriel-Gesztelyi&Green2015).Furthermore,thediskinH .Theyappearinallsizes,reachingfromsmall-
activeregionscanevolveordecayduringthediskpas-scaleactiveregionfllamentstolarge-scalequietSunfllaments,
.(2020)studiedtransitingactiveregionswhichcanreachsizesofmorethenhalfasolardiameter(.,
withspace-;).Aspecialtypeof
Imager(HMI,)andtheAtmosphericImag-quiet-Sunfllamentsarepolarcrownfllaments,whicharelocated
A107,page2of14:.
.:SolarH excessduringSolarCycle24
athighlatitudes(,1984).Theyformattheinter- observationswiththeChromosphericTele-
faceofunipolarfluxatthepolesandfluxofoppositepolarity,scopein2012–2020.
whichistransportedfromactiveregionsclosetotheequator
(PIL)appearsatYearNumberofobservingdays
mid-latitudessho