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Theory of Plasmapause Boundary Layer
Goal: Description of a physical mechanism that accounts for the formation of steep density gradients beyond the plasmapause "knee", during substorm events.
This article reports an experimental study of the Plasmasphere Boundary Layer(PBL) using MAGION 5 data. It has been published in Journal of Geophysical Research 123.https://doi.org/10.1002/2017JA024590, by G. Kotova, M. Verigin, J. Lemaire, V. Pierrard, V. Bezrukikh, and J. Smilauer.
The characteristic width of the PBL depends linearly on the time elapsed since the most recent maximum value of Kp, and on the lapse time between this maximum and the plasmapause observations.
Whistler and in-situ satellite observations (e.g. OGO5, PROGNOZ-2, GEOS-1, ISEE-1, ....) indicated that Neq(L), the equatorial plasma density in the Plasma Boundary Layer (PBL), decreases exponentially as a function of d_L, the distance from the Plasmapause (PP or Carpenter's "knee"). (Carpenter and Lemaire, 2004, THE PLASMASPHERE BOUNDARY LAYER, Annales Geophysicae, 22, p.4291)
The exponential density scale height ( H_PBL = - L / d Log[Neq] / dL) has closely the same value everywhere between sucessive vestigial PPs, up to the inner edge of the Plasmatrough : see Figs 2.2 and 2.3 in the book of Lemaire and Gringauz, 1998, THE EARTH'S PLASMASPHERE. Cambridge University Press, Cambridge; ISBN 0.521.43091.7.
The value of this closely constant density scale height (H_PBL) gradually decreases, however, with d_t, the time elapsed since the most recent formation of a new PP in the midnight MLT sector.
Sofar, none of the MHD models proposed for the formation of the PP, nor any kinetic theory for the peeling off of the PP by the enhancement of the convection velocity in the nightside oueter magnetosphere,, has been published to account for these characteristic properties observed in the PBL: i.e. the value of H_PBL independant of L, and its slow variation versus the universal time, d_t.
We are working on a kinetic theory based on plasma interchange motion, that is expected to account for both features consistently found in whistler and satellite observations.