Configuration of the high‐latitude thermosphere neutral circulation for IMF By negative and positive

Abstract

Measurements of the neutral wind in the polar F‐region from Dynamics Explorer‐2 (DE‐2) have been used to illustrate asymmetries in the Northern hemisphere neutral circulation that are dependent on the sign of the By (East‐West) component of the interplanetary magnetic field (IMF). Individual DE‐2 orbits and averaged data sets from different Universal times are presented. The data are categorized according to the sign of the hourly averaged IMF By component measured by ISEE‐3 for the hour preceding the DE‐2 measurement. The major features observed are: 1), an asymmetry in the polar cap neutral flow velocity with the region of most rapid anti‐sunward flow shifting from the dawn‐side to the dusk‐side of the polar cap as By changes from positive to negative; 2), a shift in magnetic local time of the region of entry of neutral gas into the polar cap from a location on the dawn‐side of the noon‐midnight meridian for By positive to one more biased towards the dusk‐side for By negative; 3), an enhancement in the velocities associated with the dawn, anti‐clockwise neutral vortex for By negative relative to those observed for By positive. The By neutral wind asymmetries can be explained by similar asymmetries, previously observed, in the polar ion convection pattern. They imply a direct causal relationship between solar wind/magnetosphere coupling and neutral thermospheric dynamics.