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TitreDetermination of equivalent current sources from spherical cap harmonic models of geomagnetic field variations
AuteurHaines, G V; Torta, J M
SourceGeophysical Journal International vol. 118, 1994 p. 499-514, (Accès ouvert)
Séries alt.Commission géologique du Canada, Contributions aux publications extérieures 14993
ÉditeurOxford University Press (OUP)
Documentpublication en série
Mediapapier; en ligne; numérique
Lat/Long OENS -10.0000 40.0000 65.0000 35.0000
Sujetschamps géomagnétiques; variations géomagnétiques; analyse harmoniques sphériques; méthodes analytiques; établissement de modèles; géomathématique
Illustrationssketch maps; analyses
Résumé(Sommaire disponible en anglais seulement)
The intrinsic ability of the method of spherical cap harmonic analysis to separate external and internal sources allows the calculation of equivalent ionospheric and induced currents that are able to explain variations of the geomagnetic field over a portion of the earth's surface. Formulations for current densities and current functions are derived and found to be analogous to those derived for the global case from conventional spherical harmonic analysis. Although spherical cap formulations for current density have been given by another worker, they were incorrect because of an error in defining the equivalent current. An example of the use of current functions is given by modelling variations from hourly mean values recorded at 40 geomagnetic observatories over Europe during a very quiet day in 1978. The modelling can be done spatially for each of the 24 hours separately, or spatially and temporally either by expressing each spatial coefficient as a Fourier series or by smoothing the spatial coefficients obtained from the separate hourly models.