Abstract
Abstract. Recently, Shalimov et al. (1999) proposed a new mechanism for large-scale accumulation of long-lived metallic ions in the mid-latitude ionosphere driven by planetary waves in the lower thermosphere. In this mechanism, the combined action of frictional and horizontal magnetic field forces at E-region altitudes causes the plasma to converge and accumulate in large areas of positive neutral wind vorticity within a propagating planetary wave. The present paper provides a theoretical formulation for this mechanism by modelling both horizontal and vertical plasma transport effects within a planetary wave vortex, of cyclonic neutral wind. Non-steady-state numerical solutions of the ion continuity equation show that the proposed accumulation process can enhance the ionization significantly inside the planetary wave vortex but its efficiency depends strongly on altitude, whereas on the other hand, it can be complicated by vertical plasma motions. The latter, which are driven by the same planetary wave wind field under the action of the vertical Lorentz force and meridional wind forcing along the magnetic field lines, can lead to either plasma compressions or depletions, depending on the prevailing wind direction. We conclude that, for shorter times, vertical plasma transport may act constructively to the horizontal gathering process to produce considerable E-region plasma accumulation over large sectors of a planetary wave vortex of cyclonic winds.Key words. Ionosphere (ionosphere-atmosphere interactions; mid-latitude ionosphere; sporadic E-layers) – Meteorology and atmospheric dynamics (waves and tides)
Highlights
Recent observations suggested that planetary waves could modulate the occurrence of mid-latitude E-region coherent backscatter observed with HF and VHF radars during conditions of strong sporadic E-layers (Es) in the summer night-time (Tsunoda et al, 1998; Voiculescu et al, 1999, 2000)
Paper A considered only horizontal Lorentz forces, driven by the vertical magnetic field component Bz, to act upon the meridional component of a Planetary waves (PW) cyclonic wind shear; this approach led to a simplified expression for steady-state conditions which provided only a general insight into the problem
This paper provides a starting model for the Shalimov et al (1999) mechanism of E-region metallic plasma accumulation driven by planetary waves
Summary
Recent observations suggested that planetary waves could modulate the occurrence of mid-latitude E-region coherent backscatter observed with HF and VHF radars during conditions of strong sporadic E-layers (Es) in the summer night-. Prompted by the recent findings, which indicated that PW can play a role in the generation of mid-latitude sporadic Elayers, Shalimov et al (1999) (hereafter called “paper A”) proposed a new mechanism for large-scale plasma accumulation in the mid-latitude E-region ionosphere driven by PW kinetic energy. In this process, long-lived metallic ions are forced to converge and accumulate inside large areas of horizontal wind shears within a cyclonic vortex of a propagating PW. Haldoupis: A model of planetary wave E-region plasma convergence
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