F-Region Storms and Thermospheric Dynamics

This paper reviews the composition change theory of ionospheric F2-layer storms. Recent theoretical modelling confirms that changes of the thermospheric atomic/molecular concentration ratio, resulting from energy inputs at high latitudes, are the probable cause of “negative storm effects” (electron density depletions) at mid-latitudes, and may account for “positive storm effects” (electron density increases) in the winter hemisphere. Some outstanding problems are briefly summarized.