Dynamics of the quiet thermosphere (a review)

Abstract

A survey of experimental data on thermospheric motions obtained by radiophysical methods is presented. Hydrodynamical motions in the height range 80–120 km have a clearly pronounced meteorological origin (viz. seasonal variations, longitudinal effects, local properties, etc.). A systematic statistical description of horizontal ionospheric drift measurements allows an empirical global model of motions at ionospheric levels to be obtained by the method of spaced receivers in a concerted effort of the world-wide network of stations. The prevailing zonal wind in the mid-latitude E-region is westward in the winter hemisphere and eastward in the summer hemisphere. The semi-diurnal tides at mid-latitudes and the diurnal tides at low latitudes are very intensive. At high latitudes, perhaps there is possibly an independent circulation cell that is defined by the properties of interactions of the high-latitude ionosphere with the magnetosphere and low atmosphere. In the F-region, the seasonal variations are delicately pronounced, while the manner of drift is determined mainly by the latitude. The prevailing drift during solstices is southwestward at high- and mid-latitudes and southeastward in the near equatorial zone. The transition zone coincides with the Sq-current system focus. Drift measurements in the F-region allow information about the space-time variations in ionospheric electric fields to be attained and the neutral wind evaluated at these altitudes. The results are in good agreement with incoherent scatter measurements.