The Study Of Geoelectric Storm And Pulsation In Mainland China

The two kinds of short-period variations in geoelectric field,the geoelectric storm and the gel-electric pulsation,are studied using the observation data of the geoelectric station network in the mainland of China(25°N?41°N,79°E?120°E).The research issues mainly involve the time-and frequency-domain characteristics of the short-period variations,the relationships between short-period variations of both the geoelectric and geomagnetic fields,the calculation method for quantificationally defining the earth's electromagnetic activity level using the geoelectric field change and the geoelectric disturbance index in the mainland of China.The main research results are as follows:(1)The 83 geoelectric storms(Kp?5)based on the geoelectric field minute-value data measured at the 36 stations(times)along two longitude chains(118°E and 120°E)and two latitude chains(34°N and 40°N)from Aug.2014 to Aug.2016 are analyzed using the waveform analysis method in the time domain and the nonlinear spectral estimation method in the frequency domain.As a result,the time-and frequency-domains variation characteristics for a geoelectric storm are summed up and understood in the most comprehensive level;the physical mechanism on the geoelectric field changes during a geoelectric storm is discussed,which include the short-period geo-electric field variations,their difference among different stations and between the two orthogonal observation directions of the same station,and the frequency dispersion phenomenon of geoelectric field between the two orthogonal observation directions.(2)The Pc1?Pc5 pulsation image in the geomagnetic quite days and the geomagnetic disturbance days are reconstructed based on the second-value observation data and the minute-value observation data of both the geo-electric field and the geo-magnetic field using the wavelet transform method.The results show that:the Pc1pulsation appeared during 2~h-4~h(BJT);and the Pc2?Pc5 pulsations can be decomposed in the geomagnetic quite and disturbance days,however the amplitude and frequency of Pc2?Pc5 pulsations are not the same in the two kinds of geomagnetic day.(3)Three kinds of method for calculating the geoelectric indices(for short,GEI)that include the single 3-hour index D and multiple average 3-hour index Ds are creatively put forward based on the geoelectric field changes.And the geo-electric disturbance indices,D and Ds,in the mainland of China are calculated.The calculated results show that the D and Ds calculated by the three methods are almost the same although the change of geoelectric field is quite complex,its quick disturbance components are quite abundant and there repeatedly are various influencing factors in observation,after eliminating the factors;and that most of geoelectric indices are identical to the geomagnetic indices.In other words,the difference between D and K(that is,the single 3-hour geomagnetic index)and between Ds and (?)(that is,the multiple average 3-hour geomagnetic index)is no more than 1 in value.This indicates that the geoelectric indices calculated by the three methods are reliable.Furthermore,the calculated results also show that the geoelectric index can be applied to defined the earth's electromagnetic activity level besides the geomagnetic index,which is a new method to determine the level of earth's electromagnetic activity level.From now on,the earth's electromagnetic activity level can be defined more accurately on the base of the mutual complementation of both the geoelectric activity index and the geomagnetic activity index.In addition to this,the geoelectric index also provides reference for evaluating the observation quality and monitoring the running quality of the geo-electric station network.