Geomagnetic Observations and Models

351 Pages·2011·18.583 MB·English

by  Jean L. Rasson, Hiroaki Toh, Dongmei Yang (auth.), M. Mandea, Monika Korte (eds.)

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 [e-mail]
[e-mail]
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