F-region variations prior to magnetic storms (a review)

Abstract

A review of variations in ionospheric parameters in the prestorm period obtained under analysis of particular magnetic storms (case studies) is presented. It is demonstrated that as a results of such analysis, deviations of these parameters (first of all, foF2 and TEC) are often observed on the days preceding the storm commencement (SC). Many authors pay attention to these facts and discuss their relation to the space weather parameters, season, local time, and spatial distribution and even present suggestions on possible mechanisms of their formation. It is demonstrated that the number of such publications increased substantially during 4–5 previous years. It is emphasized that the changes in the ionospheric state on prestorm days are detected not only in the “classical” parameters (foF2 and TEC), but in other ionospheric characteristics. The publications dedicated directly to the problem of ionospheric precursors, their relation to the space weather, and their possible role in forecasting coming magnetic storm are considered in detail.