LAUSR

ABSTRACT The retrospective statistical analysis of total electron content (TEC) is carried out using global ionospheric maps (GIM) for 1999–2015. TEC anomalies are analysed for 2670 earthquakes (EQ) from M6.0 to M10.0 classified into 2205 ‘non-storm’ EQs and 465 ‘storm’ EQs during geomagnetic storms. The geomagnetic storms are specified by relevant thresholds of geomagnetic indices AE, aa, ap, ap(τ) and Dst. Using sliding-window statistical analysis, moving daily–hourly TEC median μ for 15 preceding days with estimated variance bounds is obtained for each grid pixel of GIM-TEC maps. The derived ionosphere variability index, Vσ, is expressed in terms of ΔTEC deviation from the median normalized by the standard deviation σ. Vσ index segmentation is introduced specifying TEC anomaly if an instant TEC is outside the bound of μ ± 1σ. Efficiency of EQ impact on the ionosphere (Eσ) is growing with EQ magnitude and depth representing relative density of TEC anomalies within area of 1000 km radius around EQ hypocentre. Positive TEC ‘storm’ anomalies are twice as much as those of non-storm values. This observation supports dominant post-EQ TEC enhancement with Eσ peak decreasing during 12 h for daytime but growing by nighttime during 6 h after EQ followed by gradual recovery afterwards.