Prestorm ionospheric disturbances: Precursors or Q-disturbances?

Abstract

• The foF2 deviations from quiet conditions during prestorm days are, most probably, precursors of magnetic storms. • They depend on the parameters of the following magnetic storm. • The deviations are not Q-dependences. The problem of disturbances in the parameters of the F 2 layer and upper ionosphere during the days preceding onset of a magnetic storm is known already for many decades. Many publications have been dedicated to analysis of these disturbances both in the critical frequency and height of the F2 layer and in the total electron content. The majority of researchers have drawn a conclusion that such disturbances are observed prior almost to every storm, positive events (an excess of the values in the prestorm period over the corresponding values on a geomagnetically quiet day) prevailing. Moreover, some authors claimed that the aforementioned disturbances could be considered as precursors of the coming magnetic storm. A concept of the so-called Q-disturbances, according to which the disturbances during the prestorm days are not related to the coming storm but are a result of several processes (meteorological influence on the ionosphere, changes in the magnetosphere-ionosphere interaction) which sometimes cause deviations of ionospheric parameters is an alternative to the precursor concept. Arguments are presented in favor of the precursor concept. These arguments are, first of all, based on the existence of a dependence of parameters of the prestorm disturbances on parameters of the coming storm. The dependencies on the magnetic storm intensity, local time of the storm onset SO, and time from the disturbance to SO present the strongest arguments against the Q-disturbance concept. Numerous examples of these dependencies are presented. The recent publications with new experimental data on the foF 2 and TEC behavior in the prestorm period are discussed. Arguments in favor of the prestorm concept presented in these publications are briefly considered.