Abstract
ABSTRACTThe 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.
Highlights
IntroductionThe effects of earthquakes in the ionosphere are subject of intense studies during recent decades (Davies & Baker 1965; Koshevaya et al 1997; Liu et al 2006a, Liu et al 2006a, 2006b; Astafyeva & Heki 2009; Astafyeva et al 2009; Harrison et al 2010; Hayakawa & Hobara 2010; Lin 2010; Arikan et al 2012; Lin 2012; Astafyeva et al 2013; Komjathy et al 2013; Pohunkov et al 2013; Devi et al 2014; Perevalova et al 2014)
The seismic-ionospheric associations are analysed during 12 h after each of 2670 earthquakes of Richter magnitude from M6.0 to M10.0 separated to ‘storm’ class of 465 EQs and ‘quiet’ or ‘non-storm’ class of 2205 EQs worldwide from January 1999 to December 2015
The median, m, of 15 days prior to the current day at each cell of global ionospheric maps (GIM)-total electron content (TEC) map in 2.5 £ 5 of latitude / longitude grids is computed for each hour UT (0, 1, ..., 23 h) as a reference value
Summary
The effects of earthquakes in the ionosphere are subject of intense studies during recent decades (Davies & Baker 1965; Koshevaya et al 1997; Liu et al 2006a, Liu et al 2006a, 2006b; Astafyeva & Heki 2009; Astafyeva et al 2009; Harrison et al 2010; Hayakawa & Hobara 2010; Lin 2010; Arikan et al 2012; Lin 2012; Astafyeva et al 2013; Komjathy et al 2013; Pohunkov et al 2013; Devi et al 2014; Perevalova et al 2014).
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