Evaluating the Effectiveness of Using Integral Daily Es Characteristics to Identify Short-Term Ionospheric Precursors of Strong Earthquakes

-Day-to-day variations of deviations of integral daily characteristics of the sporadic E layer in different seasons in 1987, 1996, 2003-2004, and 2014 from the reference values are investigated. The analysis is conducted based on hourly measurements from Japanese ground-based vertical ionospheric sounding stations in order to identify possible short-term ionospheric precursors of crustal (surface) earthquakes with magnitudes M >= 6.5 under real observational conditions. Using the coincidence of the maxima in the variations of the considered Es characteristics at the same day on pairs of stations located hundreds of kilometers from each other, 12 possible ionospheric earthquake precursors (true alarms) and 22 false alarms, which are not followed by earthquakes of the specified range in different seasons of 1987, 1996, and 2003-2004, were found. The efficiency of identifying possible short-term ionospheric precursors of strong earthquakes is determined by the chosen method based on Hanssen-Kuipers score (Rscore), which turned out to be 0.82 for the specified time periods. It is concluded that the proposed methodology for identifying short-term ionospheric precursors of strong earthquakes can be used in real conditions.