The equatorial electrojet and the magnetosphere-ionosphere coupling—I. Analysis of low-latitude geomagnetic data

Abstract

Ground magnetic data of three low-latitude magnetic stations in China (Qiongzhong, Guangzhou and Quanzhou) are used to study the equatorial electrojet during the main phase and the initial stage of the recovery phase of strong magnetic storms. The analysis of the Z-component demonstrates that corresponding to the development of the ring current, there is a negative disturbance of ΔZ (i.e. an additional eastward electrojet), while during the recovery of D st there is a positive disturbance (a westward electrojet). This tendency can be seen at all local times, but the average amplitude varies with the local time. The effect becomes insignificant at the later stage of a storm, or in case of a storm that closely follows another one. Superposed epoch analysis, correlation analysis, X 2-analysis and analysis of variance are employed to test the results. Data from Indian stations are included to test the universality of the finding. The influence of the polar electrojet is also discussed. The research indicates the importance of distinguishing between the features at different storm phases and between effects of dynamic coupling and those of electrodynamic coupling in studying the equatorial electrojet of disturbed days.