Using field-aligned ion density profiles from a physical-numerical model of the plasmasphere, we investigated the reliability of techniques which use field line resonance measurements to remotely sense the plasmaspheric mass density rho, over L=1.6-3.4. We find that the common assumption of some functional law for the variation of rho along different field lines may lead to distorted profiles of the equatorial density rho(o) as inferred from the observed fundamental field line eigenfrequency. The tests show that for midlatitude field lines (2.3<L<3.4) a radial power law with an index m congruent to 1 might be appropriate for a large variety of solar and geomagnetic conditions, and this index well represents the mass density dependence on the outer part of the field line. Indeed, an accurate integral expression of the field line eigenperiod demonstrates that the low-altitude plasma tube provides a negligible contribution to the eigenperiod. However, at lower latitudes, higher m values are necessary to obtain correct estimates of rho(o). In this case m represents only an average index, not related to any particular variation of rho along the field line. This effective index is also significantly dependent on solar activity conditions and local time. It turns out that inferred temporal variations of rho(o) at a given low L-shell can be significantly overestimated when a fixed functional dependence for the field-aligned mass density is assumed. The performance of more sophisticated techniques which use higher harmonics is also examined.

Inference of the magnetospheric plasma mass density from field line resonances: A test using a plasmasphere model

VELLANTE, Massimo;
2006

Abstract

Using field-aligned ion density profiles from a physical-numerical model of the plasmasphere, we investigated the reliability of techniques which use field line resonance measurements to remotely sense the plasmaspheric mass density rho, over L=1.6-3.4. We find that the common assumption of some functional law for the variation of rho along different field lines may lead to distorted profiles of the equatorial density rho(o) as inferred from the observed fundamental field line eigenfrequency. The tests show that for midlatitude field lines (2.3
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11697/10624
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