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Ann. Geophys., 20, 391-404, 2002
www.ann-geophys.net/20/391/2002/
© European Geosciences Union 2002
Polarization Jet: characteristics and a model
Y. I. Galperin
1Space Research Institute, 84/32 Profsoyuznaya Str., Moscow, 117997, Russia
†passed away on the 28 December 2001
Correspondence to: L. Zelenyi (lzelenyi@iki.rssi.ru)
Abstract. Recent analysis of the
ground-based observations of the Polarization Jet (PJ) effects in the
subauroral ionosphere has shown that PJ can rapidly develop in the
near-midnight sector near the Harang Discontinuity (HD). Based on these
observations, a simple, semi-quantitative theory of the PJ formation and its
main characteristics is constructed. According to the model, PJ starts to
develop, as proposed by Southwood and Wolf, 1978, due to the penetration of the
injected energetic ions to the deeper L-shells in the presence of the westward
component of the electric field. The injection near the tip of the HD is
assumed here. The initial development stage of the PJ band, considered only
qualitatively, is supposed to lead to its inclination inward toward evening
with respect to the lines B = const. Within the model proposed, the PJ
band, once formed, will be sustained by the continuous charging at its
equatorial side, at first, mainly by the newly injected ring current ions, and
later by the plasma sheet ions convected inward through the HD. In addition, an
important charging of the PJ band occurs at its polar side by energetic
electrons drifting eastward. These electrons were either previously on the
trapped orbits or convected inward from the plasma sheet, and encounter the PJ
polar border. The model semi-quantitatively describes the main features of the
PJ events: the typical cross-PJ voltage drop ( ~ 10 kV), the resulting
double-sheet current loop feeding the PJ, the recently observed short PJ
formation time near midnight ( ~ 10 min or less) accompanied by a fast westward
HD displacement, the nearly steady-state PJ location in the evening to midnight
MLT sector and width in the ionospheric frame, the bell-shape of the electric
field latitude profile, and the long PJ lifetime (up to several hours) - all
are in rough accord with observations. Further developments of the model now in
progress are briefly described.
Key words. Magnetospheric physics
(electric fields; magnetosphere-ionosphere interactions; storms and sub-storms)
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