Remote sensing of the plasmaspheric mass density

Remote sensing of the plasmaspheric mass density

ULF waves recorded at dense latitudinal arrays can be used to monitor the magnetospheric plasma mass density. The technique is based on the determination of the field line

eigenfrequencies from a cross-spectral analysis between measurements at stations closely spaced in latitude. Assuming a reasonable functional dependence of the plasma mass density along the field lines, an estimate of the density at the apex of the field line is derived. Interesting

phenomena such as the plasmaspheric depletion and refilling which take place during geomagnetic storms can then be monitored by ground measurements. Indeed, this technique already evidenced unexpected plasmaspheric depletions (i.e. eigenfrequencies increases) at low latitudes (L < 2) during peculiar geomagnetic storms. SEGMA represents a good opportunity to investigate this phenomenology as well as to determine diurnal and seasonal variations of the plasmaspheric concentration. In the figure it is shown an example of field line resonances (identified by bright traces) at two pairs of SEGMA stations before and after the geomagnetic storm on April 3 and 4, 2004 (upper panels). In the lower panel it can be seen the increase of the resonance frequency at both the station pairs during the storm.

Recent papers:

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• M. Vellante, M. Piersanti, and E. Pietropaolo, Comparison of equatorial plasma mass densities deduced from field line resonances observed at ground for dipole and IGRF models, J.

Geophys. Res., (in review), 2014.