Ionospheric Precursors of Geomagnetic Storms. 1. A Review of the Problem

Abstract

The problem of the occurrence of disturbances of the ionospheric F2-layer parameters prior to the beginning of a geomagnetic storm is discussed. It is shown that disturbances (substantial deviations from quiet conditions) of both the critical frequency foF2 and the total electron content (TEC) in an ionospheric column are found in many studies a few hours and sometimes even two days before the SC (sudden storm commencement) moment. The amplitudes of the aforementioned disturbances are on average of 30–60%, however, they can exceed 100% in some cases. Deviations from the quiet conditions of both signs are possible; however, positive prestorm disturbances of foF2 and TEC are more common.