Effects of Geomagnetic Storms in the Low-Latitude Ionosphere

Abstract

A wide range of changes in parameters of the low-latitude ionosphere has been revealed during the periods of three intense geomagnetic storms that occurred in different seasons of 2015. Ionospheric parameters, according to the data from ionosondes (ionograms), include critical frequencies fоF2, foE, and foEs; the degree of diffuseness of signals; the presence of lateral reflections; the multihop pattern of vertical-incidence ionospheric sounding (VIS); the effect of blocking signal reflections from the F2 layer by the Es layer; and the presence of М-type modes. The analysis was based on the data from ionosondes at low-latitude stations in Athens, Greece, and Nicosia, Cyprus. The following results were obtained. The spring storm was characterized by the presence of lateral reflections, greater diffuseness in the F2 layer, and an increased number of reflections during VIS during daytime hours compared to nighttime hours. The summer storm was characterized by very frequent appearance of sporadic Es layers, the occurrence of М-type reflections, and the effect of blocking. The specific analysis of the winter storm shows that the thick Es layer stretched along the Earth’s surface over a distance of no less than 800 km and had a lifetime of about 7 h.