Role of neutral atmospheric dynamics in cusp density and ionospheric patch formation

Abstract

Ionospheric patches are islands of plasma transiting the polar cap, with density at least double the surrounding background plasma. Since their discovery 25 years ago, many mechanisms for their production have been proposed and examined. However all of these mechanisms consider only electric fields and charged particles as candidate mechanisms for patch formation, particularly transient changes in these electrodynamic terms. Here for the first time, we call attention to the role of thermospheric dynamics in Patch formation. We show that the thermospheric response to transient heating events near the cusp must significantly increase exospheric densities over the cusp, and also that a plausible doubling of these densities near and above 400 km altitude leads to a new patch production mechanism. The underlying processes must drive a solar cycle variation of how many hours UT experience strong polar patches and scintillation. These processes must be added to present thinking and modeling. Copyright 2007 by the American Geophysical Union.