New parameterization of external and induced fields in geomagnetic field modeling, and a candidate model for IGRF 2005

Nils Olsen, T.J. Sabaka, F. Lowes

    Research output: Contribution to journalJournal articleResearchpeer-review

    Abstract

    When deriving spherical harmonic models of the Earth's magnetic field, low-degree external field contributions are traditionally considered by assuming that their expansion coefficient q(1)(0) varies linearly with the D-st-index, while induced contributions are considered assuming a constant ratio Q(1) of induced to external coefficients. A value of Q(1) = 0.27 was found from Magsat data and has been used by several authors when deriving recent field models from Orsted and CHAMP data. We describe a new approach that considers external and induced field based on a separation of D-st = E-st + I-st into external (E-st) and induced (I-st) parts using a 1D model of mantle conductivity. The temporal behavior of q(1)(0) and of the corresponding induced coefficient are parameterized by E-st and I-st, respectively. In addition, we account for baseline-instabilities of D-st by estimating a value of q(1)(0) for each of the 67 months of Orsted and CHAMP data that have been used. We discuss the advantage of this new parameterization of external and induced field for geomagnetic field modeling, and describe the derivation of candidate models for IGRF 2005.
    Original languageEnglish
    JournalEarth, Planets and Space
    Volume57
    Issue number12
    Pages (from-to)1141-1149
    ISSN1343-8832
    Publication statusPublished - 2005

    Keywords

    • spherical harmonic analysis
    • geomagnetic reference model
    • induction
    • magnetospheric currents
    • IGRF/DGRF

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