Earth Planets Space, Vol. 58 (No. 4), pp. 451-461, 2006
S. Vennerstrom1, T. Moretto2, L. Rastätter2, and J. Raeder3
1Danish National Space Center, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark
2NASA Goddard Space Flight Centre, Greenbelt, Maryland, U.S.A.
3Institute for the Study of Earth, Oceans and Space, University of New Hampshire, Durham, New Hampshire, U.S.A.
(Received November 24, 2004; Revised August 12, 2005; Accepted August 22, 2005; Online published April 14, 2006)
Solar wind generated magnetic disturbances are currently one of the major obstacles for improving the accuracy in the determination of the magnetic field due to sources internal to the Earth. In the present study a global MHD model of solar wind magnetosphere interaction is used to obtain a physically consistent, divergence-free model of ionospheric, field-aligned and magnetospheric currents in a realistic magnetospheric geometry. The magnetic field near the Earth due to these currents is analyzed by estimating and comparing the contributions from the various parts of the system, with the aim of identifying the most important aspects of the solar wind disturbances in an internal field modeling context. The contribution from the distant magnetospheric currents is found to consist of two, mainly opposing, contributions from respectively the dayside magnetopause currents and the cross-tail current. At high latitudes the field-aligned component is of partidular interest in connection with internal field-modelling. In the altitude regime of 400-800 km (typical for low Earth orbit satellites) the ionospheric currents are found to contribute significantly to the disturbancance, and account for more than 90% of the field-aligned disturbance. The magnetic disturbance field from field-aligned currents (FACs) is basically transverse to the main field, and they therefore contribute with less than 2% to the disturbance in total field intensity. Inhomogeneity in ionospheric conductance is identified as the main cause of main-field disturbance in the field-aligned direction. These disturbances are associated with the ionospheric Pedersen currents, and may introduce systematic errors in internal field models.
Key words: Earth's magnetic field, MHD modeling, solar wind, ionosphere, magnetosphere, quiet conditions.