Abstract
Abstract The method of 1D spherical elementary current systems (SECS) is a new way for determining ionospheric and field-aligned currents in spherical geometry from magnetic field measurements made by a low-orbit satellite. In contrast to earlier methods, the full ionospheric current distribution, including both divergence-free and curl-free horizontal currents, as well as field-aligned currents, can be determined. Placing infinitely many 2D SECSs of identical amplitudes at a constant latitude results in two types of 1D SECSs, which are independent of longitude, and by superposition can reproduce any ionospheric and field-aligned current system with the same property. One type of the 1D SECSs is divergence-free and toroidal with a poloidal magnetic field, and the other type is curl-free and poloidal. Associated with the divergence of the curl-free type are radial currents. The magnetic field of the combined curl-free 1D SECS and field-aligned currents is toroidal and restricted to the region above the ionosphere. Ionospheric currents are determined by placing several 1D SECSs at different latitudes and choosing their amplitudes in such a way that their combined magnetic field as closely as possible fits the one measured by the satellite. The 1D SECS method has been tested using both modeled and real data from the CHAMP satellite, and found to work excellently in 1D cases.
Highlights
Magnetic measurements from ground-based magnetometers or satellites can be employed to determine ionospheric electric currents, which are of interest in the ionospheremagnetosphere research
Placing curlfree 1D spherical elementary current systems (SECS) at the desired scale length assures that the current system at this scale lengths will be optimally matched to the magnetic field data
A new method for determining the full ionospheric current distribution, including horizontal and field-aligned currents, in spherical geometry from low-orbit satellite-based magnetic measurements has been introduced. This 1D SECS method is applicable in cases that are nearly onedimensional and stationary during the satellite overflight
Summary
Magnetic measurements from ground-based magnetometers or satellites can be employed to determine ionospheric electric currents, which are of interest in the ionospheremagnetosphere research. Ground-based measurements by themselves can only yield ionospheric equivalent currents (Fukushima, 1976), whereas measurements above the ionosphere can be used to determine the full current distribution, including horizontal and field-aligned currents (FAC). With additional information on ionospheric electric fields and conductances, ground-based measurements can yield the full ionospheric current distribution (Untiedt and Baumjohann, 1993) but, unlike magnetic measurements, these are not and extensively available. The technique commonly applied to magnetic satellite data in order to determine ionospheric currents was developed by Olsen (1996). He assumed that only horizontal, not field-aligned currents, contribute to the magnetic field component parallel to the geomagnetic field. Limitations of Copyright c The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences; TERRAPUB
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