Physics
Scientific paper
Jul 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999jastp..61..867l&link_type=abstract
Journal of Atmospheric and Solar-Terrestrial Physics, Volume 61, Issue 11, p. 867-878.
Physics
10
Scientific paper
It has been shown that no hydrostatic/barometric model for a rotating plasmasphere is able to fit the equatorial electron density distributions observed by the ISEE satellite for L<8, following prolonged periods of quite magnetic conditions. Indeed, it has been found that all these saturated plasma density profiles are characterized by scale heights which are independent of L, while those corresponding to any hydrostatic/barometric models are always increasing functions of L. Furthermore, all calculated barometric equatorial density profiles have a minimum value at an equatorial distance given by Lo=(GME/Ω2R3E)1/3=6.6(ΩE/Ω)2/3, depending on the value of the angular rotational speed, Ω: Lo<=6.6 for Ω/ΩE>=1. The position of this minimum is independent of the particle velocity distribution function (VDF) assumed (i.e. on the energy spectrum of the ions and electrons); the value of the minimum density depends on the temperature and density at the low altitude reference, as well as on the kappa index of the Lorentzian VDF assumed to calculate the barometric model. There is no evidence for such a minimum value in the observed equatorial density profiles of ISEE. This is considered as a second indication that the plasmasphere is not in hydrostatic/barometric equilibrium. Next, it is shown that for L>Lo all barometric models are convectively unstable with respect to interchange and quasi-interchange. Therefore, it is not surprising that observed density profiles do not fit any of the profiles corresponding to corotating barometric models. A final indication that the plasmasphere is not in hydrostatic equilibrium but in a state of continuous hydrodynamic expansion comes from the fact that the total plasma pressure at the outer edge of the magnetosphere is lower than the kinetic pressure predicted by barometric models at large radial distances. As a consequence of this pressure unbalance, the plasmasphere is expected to expand continuously like the solar corona. Evidence for such a plasmaspheric wind had already been inferred earlier from the study of the ion density profiles obtained from the OGO-5 mission.
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