Comparison of variations in the F2 layer critical frequency before the strong Italian earthquakes and during the magnetic storm: Data of the stations for ground-based vertical sounding of the ionosphere

Abstract

The possible seismic ionospheric effects before two strong earthquakes in Italy, which took place near Rome station (January 7, 1962, M = 6.0; April 5, 1998, M = 5.3), have been studied using the data of several European stations for ground-based vertical sounding of the ionosphere. An analysis of the behavior of the foF2 critical frequencies for the earthquake that occurred on January 7, 1962, made it possible to simultaneously consider the effects, originating during earthquake preparation under quiet geomagnetic conditions and caused by the magnetic strom that began on January 10, 1962, using a unified technique. It has been indicated that the distinguished precursor effects of two considered earthquakes with magnitudes not more than 6.0 are localized in the region with an epicentral distance of about 400 km, whereas the disturbances caused by the magnetic storm are of a planetary character. The amplitude of foF2 seismic ionospheric disturbances is much smaller than the maximal variations caused by the magnetic storm; however, the absolute value of this amplitude is a factor of 1.5 as large as the standard deivation from the monthly median.