Study on the geoelectric index (GEI): taking the geoelectric field observation in mainland China as an example

This paper reports three methods of researching the geoelectric index (GEI) based on the ratio between the variation amplitude of geoelectric field on an index calculation day and that on a magnetically quiet day, and uses the three methods to process the observation data of 18 geoelectric stations in China in September 2017. Results showed that, each method has obtained 4096 single-station geoelectric indices D and 240 multi-station average geoelectric indices Ds, all 3-hour indices. Comparing the geoelectric indices with the geomagnetic indices of the 18 stations, it can be understood that: 87.35%-88.26% of indices D are the same with the single-station geomagnetic indices (K) over bar or have only a difference of 1 from the indices K, and 97.08%-97.50% of indices Ds are the same with the multi-station average geomagnetic indices (K) over bar over bar or have only a difference of 1 from the indices K over bar . The high consistency between two kinds of indices shows that the methods of calculating geoelectric index are practicable, and that the calculated indices D and Ds are reliable. The geoelectric field, as an independent observation, should have a criterion to judge the interference.