Variations of the auroral electrojet belt during substorms

Both aurora display and auroral electrojet, as the most important manifestations of the energy coupling between the magnetosphere and the ionosphere, are resulted from particle precipitation, and greatly enhanced during substorms. 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 electrojet belt is divided by Harang discontinuity into two parts: the minor eastward electrojet in afternoon sector and the major westward electrojet in midnight-morning sector. The former shifts equatorward when AE increases, just as the auroral oval does; the latter is divided into two sections: the midnight section shifts poleward when AE increases, while the morning section shifts equatorward. A study on physical mechanism responsible for these differences reveals that the principal factor controlling the midnight-morning westward electrojet is ionospheric conductivities, while the principal factor controlling the afternoon eastward electrojet is electric field, instead of conductivities.