Variability of sporadic E-layer semi transparency (f_oE_s-f_bE_s)with magnitude and distance from earthquake epicenters to vertical sounding stations

Abstract. Variations of the E_s-layer semi transparency co-efficient were analyzed for more than 100 earthquakes with magnitudes M > 4 and depths h < 100 km. Data of mid latitude vertical sounding stations (Kokubunji, Akita, and Yam-agawa) have been used for several decades before and after earthquake occurrences. The semi-transparency coefficient of E_s-layer X = (f_oE_s – f_bE_s)/f_bE_s can characterize, for thin layers, the presence of small scale plasma turbulence. It is shown that the turbulence level decreases by ~ 10% during three days before earthquakes probably due to the heating of the atmosphere. On the contrary, the turbulence level increases by the same value from one to three days after the shocks. For earthquakes with magnitudes M > 5 the effect exists at distances up to 300 km from the epicenters. The effect could also exist for weak (M ~ 4) and shallow (depth < 50 km) earthquakes at a distance smaller than 200 km from the epicenters.