Cyclonic disturbances and their consequences in the thermosphere

We draw attention to the possible existence of cyclonic type of disturbances in the thermosphere which are created by localized energy sources in the vicinity of the nightside (and possibly the dayside) auroral oval. Due to the Coriolis force and the character of F‐region ion motions, cyclonic disturbance cells of limited extent (3000 to 5000 km) may appear in conjunction with auroral substorms or more prolonged geomagnetic activity. Owing to prevailing thermospheric winds, these disturbances can be expected to drift equatorwards to mid‐latitude regions. The disturbance zone can be characterized in terms of a cyclonic wind pattern and significant changes in thermospheric neutral gas composition. This latter effect results in decreased plasma densities in the F‐region for the lifetime of the disturbance.