Geomagnetic Observations and Models PDF
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Geomagnetic Observations and Models IAGA Special Sopron Book Series Volume 5 SeriesEditor BengtHultqvist TheSwedishInstituteofSpacePhysics,Kiruna,Sweden The International Association of Geomagnetism and Aeronomy is one of the eight AssociationsoftheInternationalUnionofGeodesyandGeophysics(IUGG). IAGA’sMission TheoverallpurposeofIAGAissetoutinthefirststatuteoftheAssociation: • to promote studies of magnetism and aeronomy of the Earth and other bodies of the solar system, and of the interplanetary medium and its interaction with thesebodies,wheresuchstudieshaveinternationalinterest; • to encourage research in these subjects by individual countries, institutions or personsandtofacilitateitsinternationalcoordination; • toprovideanopportunityonaninternationalbasisfordiscussionandpublica- tionoftheresultsoftheresearches;and • topromoteappropriatestandardizationsofobservationalprograms,dataacqui- sitionsystems,dataanalysisandpublication. Volumesinthisseries: TheEarth’sMagneticInterior EditedbyE.Petrovský,D.Ivers,T.HarinarayanaandE.Herrero-Bervera AeronomyoftheEarth’sAtmosphereandIonosphere EditedbyM.A.Abdu,D.PanchevaandA.Bhattacharyya TheDynamicMagnetosphere EditedbyW.LiuandM.Fujimoto TheSun,theSolarWind,andtheHeliosphere EditedbyM.P.MirallesandJ.SánchezAlmeida GeomagneticObservationsandModels EditedbyM.MandeaandM.Korte Fortitlespublishedinthisseries,goto http://www.springer.com/series/8636 Geomagnetic Observations and Models Editors Mioara Mandea InstitutdePhysiqueduGlobe,Paris,France Monika Korte GFZGermanResearchCentreforGeosciences Potsdam,Germany 123 Editors Prof.Dr.MioaraMandea Dr.MonikaKorte UniversitéParisDiderot GFZGermanResearchCentre InstitutdePhysiqueduGlobede forGeosciences Paris Telegrafenberg rueThomasMann5 14473Potsdam,Germany 75205Paris,France [email protected] [email protected] ISBN978-90-481-9857-3 e-ISBN978-90-481-9858-0 DOI10.1007/978-90-481-9858-0 SpringerDordrechtHeidelbergLondonNewYork ©SpringerScience+BusinessMediaB.V.2011 AllRightsReservedforChapters7,10and12 Nopartofthisworkmaybereproduced,storedinaretrievalsystem,ortransmittedinanyformorby anymeans,electronic,mechanical,photocopying,microfilming,recordingorotherwise,withoutwritten permissionfromthePublisher,withtheexceptionofanymaterialsuppliedspecificallyforthepurposeof beingenteredandexecutedonacomputersystem,forexclusiveusebythepurchaserofthework. Cover illustration: Models of magnetic fields produced by the core or the lithosphere, are shown at the top of the core or respectively Earth’s surface. These models are obtained from geomagnetic highaccuracydata,providedbyground(magneticobservatoriesandrepeatstations),aeromagneticand satellite measurements. Figure produced by Martin Rother (Helmholtz-Zentrum Potsdam, Deutsches GeoForschungsZentrum-GFZ). Printedonacid-freepaper SpringerispartofSpringerScience+BusinessMedia(www.springer.com) Foreword by the Series Editor The IAGA Executive Committee decided in 2008, at the invitation of Springer, to publishaseriesofbooks,whichshouldpresentthestatusoftheIAGAsciencesatthe timeoftheIAGA2009ScientificAssemblyinSopron,Hungary,the“IAGASpecial SopronSeries”.Itconsistsoffivebooks,oneforeachoftheIAGADivisions,which togethercovertheIAGAsciences: DivisionI–InternalMagneticField DivisionII–AeronomicPhenomena DivisionIII–MagnetosphericPhenomena DivisionIV–SolarWindandInterplanetaryField DivisionV–GeomagneticObservatories,SurveysandAnalyses. The teams of Editors of the books contain members of the IAGA Executive Committee and of the leadership of the respective Division, with, for some of the books,oneorafewadditionalleadingscientistsintherespectivefields. The IAGA Special Sopron Series of books are the first ever (or at least in many decades)withtheambitiontopresentafullcoverageofthepresentstatusofallthe IAGA fields of the geophysical sciences. In order to achieve this goal each book contains “overview papers”, which together summarize the knowledge of all parts of the respective field. In book no. 5, on geomagnetic observations, all papers are ofthatkind.Thesemajorreviewpapersare,intheotherfourbooks,complemented withinvitedreviewsofspecialquestionspresentedinSopron.Finally,insomeofthe booksafewshort“contributed”papersofspecialinterestareincluded.Thus,wehope thebookswillbeofinteresttoboththosewhowantarelativelyconcisepresentation ofthestatusofthesciencesandtothosewhoseekthemostrecentachievements. I want to express my thanks to the editors and authors who have prepared the contentofthebooksandtoPetravanSteenbergenatSpringerforgoodcooperation. Kiruna,Sweden BengtHultqvist November2010 v Contents 1 TheGlobalGeomagneticObservatoryNetwork . . . . . . . . . . . . 1 JeanL.Rasson,HiroakiToh,andDongmeiYang 2 MagneticSatelliteMissionsandData . . . . . . . . . . . . . . . . . . 27 NilsOlsenandStavrosKotsiaros 3 RepeatStationActivities . . . . . . . . . . . . . . . . . . . . . . . . . 45 DavidR.BarracloughandAngeloDeSantis 4 AeromagneticandMarineMeasurements . . . . . . . . . . . . . . . 57 MohamedHamoudi,YoannQuesnel,JérômeDyment, andVincentLesur 5 Instruments and Methodologies for Measurement oftheEarth’sMagneticField . . . . . . . . . . . . . . . . . . . . . . 105 IvanHrvoicandLawrenceR.Newitt 6 ImprovementsinGeomagneticObservatoryDataQuality . . . . . . 127 JanReda,DanielleFouassier,AncaIsac,Hans-JoachimLinthe, JürgenMatzka,andChristopherWilliamTurbitt 7 Magnetic Observatory Data and Metadata: Types andAvailability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 SarahJ.Reay,DonaldC.Herzog,SobhanaAlex, EvgenyP.Kharin,SusanMcLean,MasahitoNosé, andNataliaA.Sergeyeva 8 GeomagneticIndices . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 MichelMenvielle,ToshihikoIyemori,AurélieMarchaudon, andMasahitoNosé 9 Modelling the Earth’s Magnetic Field from Global toRegionalScales. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229 Jean-JacquesSchottandErwanThébault 10 TheInternationalGeomagneticReferenceField . . . . . . . . . . . . 265 SusanMacmillanandChristopherFinlay 11 GeomagneticCoreFieldModelsintheSatelliteEra. . . . . . . . . . 277 VincentLesur,NilsOlsen,andAlanW.P.Thomson vii viii Contents 12 InterpretationofCoreFieldModels . . . . . . . . . . . . . . . . . . 295 WeijiaKuangandAndrewTangborn 13 MappingandInterpretationoftheLithosphericMagnetic Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311 MichaelE.PuruckerandDavidA.Clark Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339 Introduction The magnetic field is one of the oldest observable Earth properties. The first mea- suredgeomagneticfieldcomponent,declination,waslinkedtotheuseofcompasses, having their origin in the human curiosity of the north-pointing characteristics of loadstone.Startingwiththe16th centurymeasuringtheEarth’smagneticfieldcom- ponents (firstly only declination, thereafter also inclination and finally the full field vector)hasbecomemoresystematicandkeptimprovingovertime. Observation and modeling are the prerequisites to describe the Earth’s magnetic field and to understanding the processes generating it. It is the determination of DivisionV,withitsthreeworkinggroups,tosupport (i) theglobaleffortsofmeasuringthegeomagneticfieldanditschangesby (ii) encouragingcommondatastandardsandglobaldataavailabilityand (iii) providingglobalmagneticfieldmodelsofcorefieldandlithosphere. Thescopeofthisbookisdefinedbytheactivitiesinthethreeworkinggroupsand coversthethreetopics:geomagneticobservation,dataandmodeling. A network of ground-based geomagnetic observatories forms the backbone of Earth’smagneticfieldobservationsinceAlexandervonHumboldt’stimeintheearly 19thcentury.Todaythesecontinuouslyrecordingstationsareanimportantcomple- menttothenewwealthofdataobtainedfromsatellitesobservingtheEarth’smagnetic field from low Earth orbits. In the first chapter, an overview over the present obser- vatorynetworkisgivenwithspecialemphasisonrecenteffortstoimprovetheglobal coverage. The era of satellites observing the full magnetic vector field relatively close to Earth started in 1979/1980, when the MAGSAT satellite was in orbit for 6 months. Longertermfieldmonitoringofthiskind,however,onlystarted20yearslater,when theDanishØrsted,theGermanCHAMPandtheArgentinianSAC-Csatelliteswere launched in close succession. Both Ørsted and CHAMP have continued to provide globalmagneticfielddatain2010.Afollow-upmissionconsistingofaconstellation of 3 satellites is in preparation by ESA under the name of Swarm. All aspects of magneticsatellitemissionsarediscussedinChapter2. Satellites provide a limited resolution of the field distribution at the Earth’s sur- face due to their orbit altitude. Repeat station measurements carried out in regular time intervals on well-defined locations supplement observatory recordings, which are spatially sparse in large parts of the world. Aeromagnetic and marine measure- mentsarededicatedtodetailedmappingofthe(regional)lithosphericmagneticfield. ix x Introduction Chapters3and4provideinformationonthepurposesandtechniquesofthesekinds ofobservations,highlightingrecentactivities. Chapter 5 gives an overview over commonly used instruments to measure the Earth’s magnetic field and particularly outlines new developments to facilitate the recordingofhigh-qualitygeomagneticfielddata. Dataquality,documentationandavailabilityarethekeyrequirementsforsuitable interpretationtogainabetterunderstandingofallthegeomagneticfieldcontributions andtheirtemporalvariations.Forsatellitedata,thepropercalibrationofvectormea- surements isachallenging task.Data processing, however, isgenerally done by the institution in charge of the mission, ensuring a fixed data format, a homogeneous quality level and an easy data availability. All other kinds of observations, how- ever,includingthosebygeomagneticobservatories,arecarriedoutbyverydifferent institutions and agencies in individual countries. Common standards for data qual- ity,commondataformats,andglobaldataavailabilityaredifficultissues.Chapters6 and7describetheeffortsbythegeomagneticcommunity,IAGAworkinggroupsand organisationsliketheWorldDataCenterstoimprovequalityandglobalavailability ofgeomagneticdataandensureagooddocumentationofthem. Magneticmeasurementsfromanyplatforminfactgivethesumofallfieldcontri- butionsfromthesourcesinternalandexternaltoEarth.Astraightforwardseparation of the individual contributions is impossible and many scientific studies deal with different aspects of this problem. Approximate descriptions of the strength of dif- ferentexternal variations,however, areprovided bygeomagnetic indices.These are obtained by standardized rules as special data products, mostly from geomagnetic observatoryrecordings.TheplanetarygeomagneticactivityindexKpprobablyisthe most widely known, but several other indices more suitable for special applications exist. Chapter 8 provides a comprehensive overview of magnetic indices and their relevance. Geomagneticfieldmodelsobtainedbyinversetechniquesfromthemeasureddata are widely used tools for studies of secular variation and the underlying processes intheEarth’score.Moreover,theycanprovidedeclinationpredictionsforanyloca- tion on Earth for navigational purposes. The most commonly used global modeling techniqueissphericalharmonicanalysis.Thismethodandothertechniquesapplied to obtain global or regional models of the magnetic core or lithospheric field are describedindetailinChapter9. ThefollowingchapterisdedicatedtoanimportantIAGAproduct,theInternational Geomagnetic Reference Field IGRF. This field model consists of standardized descriptions of the geomagnetic core field, is updated every 5 years with predictive secular variation for the next 5 years, is easily available and field predictions from thismodelcanbeobtainedinteractivelyfromseveralwebsites. The IGRF is extremely useful for all applications where a standard reference is needed, but for scientific applications requiring the highest possible accuracy or including descriptions of some external or lithospheric field contributions, more specialized models are developed. After a brief overview, three examples of most recently obtained versions of this kinds of core field models are discussed in Chapter11.Thenextchapterprovidesanoverviewoverimportantresultsandfindings regarding the geodynamo process as obtained from recent core field models. More about this topic can be found in the book by Division I within this series. Finally, Chapter 13 deals with mapping and interpreting the lithospheric field, including a brief summary of the enormous efforts undertaken by several international groups
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