Dependence of the high-latitude lower thermospheric wind vertical vorticity and horizontal divergence on the interplanetary magnetic field

We analyze the vertical component of vorticity and the horizontal divergence of the high-latitude neutral wind field in the lower thermosphere during the southern summer time for different interplanetary magnetic field (IMF) conditions with the aid of the National Center for Atmospheric Research thermosphere ionosphere electrodynamics general circulation model, with the following results. (1) The mean neutral wind pattern in the high-latitude lower thermosphere is dominated by rotational flow, imparted primarily through the ion drag force rather than by horizontally divergent flow.

(2) The vertical vorticity depends on the IMF. (3) The difference vertical vorticity, obtained by subtracting values with zero IMF from those with nonzero IMF, is much larger than the difference horizontal divergence for all IMF conditions. (4) The effects of IMF penetrate down to 106 km altitude.