The diurnal variation of geo-electric field along the longitude and latitude chains in China mainland

This paper has studied the time and frequency characteristics of the geo-electric field diurnal variation along the two longitude chains and the two latitude chains,using the data of the geo-electric field observed at the 37 stations along the chains.Accordingly,the following significant results are obtained: the variation appears mainly as semi-diurnal waves twice a day at most of the stations,approximately before and after the noon;according to the big to small order of the FFT amplitude spectrums,the main periods of the diurnal variation are 12.4 h/12 h,8 h,24 h,etc,which are in accordance with the periods of the tidal harmonic components;the latitude effect on diurnal variation is manifested by the amplitude changing with latitude along a longitude chain,and the longitude effect is shown as phase difference consistent with the local-time difference between the stations at the same latitude.Furthermore,the amplitude of the diurnal variation is related with the Loyd season,which reduces orderly in J-,E-and D-seasons.The possible reasons for the main periodic components of the diurnal variation have been discussed,as a result,it is believed that the variation of the ground eddy current intensity caused by lunisolar tidal forces and the space electromagnetic activity aroused by the solar wind jointly produce the semi-diurnal period components of the geo-electric diurnal variation.