The Inversion Of Internal-External Equivalent Current System Of Geomagnetic S_q And Its Research On Application

The seismic fault zones are quite active in China because of the long time continuous compression from the Pacific plate, the India plate and the Philippine plate. Frequent earthquakes have brought a huge disaster and loss not only to the lives and property safety of people but also the economic development of the country. Large amount of observational information indicate that electromagnetic radiation detection can play important role in earthquake monitoring and prediction. And the electromagnetic satellite observation technology has attracted more and more attention for international scholars. In order to establish a stereo earthquake monitoring system. The Seismo-Eelectromagnetic Satellite project was took in China in 2007. The satellite will be launched in 2016.The ionosphere is the partly ionoized region at upper atmosphere,and the magnetosphere is above it with air fully ionized. Magnetosphere-ionosphere is not only affected by solar activity, but also from the earth and its lower atmosphere, so there are complex physical and chemical coupling proceses among the spheres. Due to high dynamic, multi-scale and special space environment, it is difficult to study of the magnetosphere-ionosphere current system. The earthquake application study by using the magnetosphere-ionosphere current system is still at an exploration stage. Based on the previous research, the spherical harmonic analysis is used in this paper to build the internal and external Sq equivalent current system, and the inversion results are compared with F10.7cm solar radio flux, geomagnetic activity index Dst. Finally, the relationship between the phenomenon of low point displacement in geomagnetic vertical component and the equivalent external and internal current systems has been discussed,which is expected to provide certain technological and theoretical supports for seismo-ionospheric study.In this paper, the data observed at the global geomagnetic stations (INTERMAGNET) were selected from 2001 to 2012. Based on the spherical harmonic analysis, the internal and external Sq equivalent current system inversion model was established. After then, the inversion current results were compared with F10.7cm solar radio flux and geomagnetic activity index Dst to build their relationship. At last, the internal and external current systems were analyzed around the earthquakes with precursors of low point displacement in geomagnetic field,, in whcih the possible relation among them were investigated. The main research conclusions are as follows:(1) The current intensity of northern vortex center in internal and external equivalent current system has a peak in July or August each year, and there is an inverse phenomenon on southern hemisphere, which showing an obvious feature that the current intensity is higher in summer than in winter. This result shows that Sq is mainly controlled by the Sun. And internal current system is affected by the Sun and the conductivity of the Earth.(2) During geomagnetic storm activity, the southern and northern current vortex always increased firstly and then decreased quickly, showing simuteneously variation with Dst index, whatever in internal field or external field. In the year with strong but fewer geomagnetic storms, the current vortex intensity varied more regularly with Dst index. The northern vortex variations were stronger than the southern one.(3) The annual averaged current intensity of vortex center in internal and external equivalent current system exhibited same solar cycles of 11 years with the F10.7 cm solar radio flux. The current intensity of vortex center in external field presented a good linear correlation with F10.7, being 0.93 and 0.9 at southern and northern hemisphere respectively, while the linear correlation coefficient of internal field with F10.7 was lower, being 0.63 and 0.79 at both hemispheres.(4) On that day when low point displacement in geomagnetic vertical component occurred, the internal and external equivalent current intensity of their vortex centers both decreased, especially the internal current system with larger reducing magnitude. This phenomenon has well been presented on geomagnetic quiet day in the northern hemisphere, such as on May 9, and June 13 2008. In addition, the location of the current vortex showed a certain displacement in latitude, which was also apparent in the internal field. All of these seemed to demonstrate that the low point displacement in geomagnetic feild had closer relationship with internal field.