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Enhancement of auroral activity and intensification of auroral electrojet are the most important manifestations of the magnetosphere-ionosphere coupling. Both aurora and electrojet result from the same mechanism-charged particle precipitation, however, they have rather different behaviors and AE-dependences. In this paper, the dynamic characteristics of the auroral electrojet belt are studied by using equivalent current systems deduced from ground-based magnetic records. The results show that the auroral electrojet belt is divided by the Harang discontinuity into two parts: the afternoon-dusk section with minor eastward electrojet and the midnight-morning section with major westward electrojet, the latter is divided into two subsections: the midnight section and the morning section. Along with AE increasing in substorm expansion phase, the whole auroral oval expanses equatorward, however, the different sections of the auroral electrojet exhibit different dynamic behaviors: the afternoon-dusk and morning sections drifts equatorward, just as the auroral oval does, while the midnight section drifts poleward. A study on electrodynamics responsible for these differences reveals that the principal controlling factor is different for different sections of the electrojet: the afternoon-dusk eastward electrojet and the morning westward electrojet are mainly controlled by the magnetospheric convection electric field, corresponding to DP2 currents of the directly driven process, while the midnight westward electrojet largely depends on the ionospheric conductivities, corresponding to DP1 currents of the unloading process. |
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