F-Region Variations Prior to Magnetic Storms (a Review)

Abstract

The paper presents a review of variations in ionospheric parameters in the prestorm period obtained from an analysis of particular magnetic storms (case studies). It is demonstrated that, as a result of such analysis, deviations of these parameters (primarily, 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 space weather parameters, season, local time, and spatial distribution, and even offer suggestions on possible mechanisms of their formation. It is demonstrated that the number of such publications increased substantially in the preceding 4–5 years. It is emphasized that changes in the ionospheric state on prestorm days are detected not only in the “classical” parameters (foF2 and TEC), but also in other ionospheric characteristics. Publications dedicated directly to the problem of ionospheric precursors, their relation to space weather, and their possible role in forecasting coming magnetic storm are considered in detail.