High-latitude ground-based observations of the thermosphericion-drag time constant

Abstract

From previous studies, it has been conclusively demonstrated that F-region thermospheric winds follow, but generally lag behind, the ion drift pattern of magnetospheric convection. Analysis of the ion-neutral momentum exchange equation shows that ion-drag and thermal pressure are the major contributors to neutral momentum forcing at F-region heights with relatively minor effects from coriolis, advection and viscous forces. An ion-neutral coupling time constant (e-folding time) has been defined which describes the time taken for the neutral gas velocity to approach the ion velocity after a step change in convection. In this study, F-region ion drift and neutral winds have been observed by the ElSCAT tristatic incoherent scatter facility and a ground-based Fabry-Perot interferometer, respectively, from northern Scandinavia. The e-folding time varies in the range 0.5 - 6.5 hours, with an average of 1.8 and 3.3 hours for a geomagnetically active and quiet period, respectively, which compares well with previous satellite measurements of 0.5 - 3.5 hours.