ABSTRACT
This chapter describes the energy source responsible for the disturbance effects and its parameterization by geomagnetic activity indices. It discusses of ionospheric storm effects at middle latitudes, which begins with a brief description of the basic storm morphology and a summary of possible disturbance mechanisms. The chapter continues with the outline of a thermospheric-ionospheric storm model and with a compilation of ionospheric storm simulation studies. During less disturbed conditions it was found that with increasing magnetic activity the F-region ionization density decreased during the day and sometimes increased during the night. A prominent F-region feature associated with this ionization source is the auroral oval density enhancement, which has been denoted as plasma torus. The completely different disturbance behavior of the ionosphere two comparable locations indicates that the global morphology of ionospheric storms is complex. The distinction between positive and negative ionospheric storms represents the simplest possible classification.
