Geomagnetic responses to the convection field, field-aligned current and auroral electrojet

Convection field, field-aligned current and auroral electrojet are all very important processes in the magnetosphere-ionosphere coupling. The time sca le of their evolution is about several minutes to half an hour. In this pap er geomagnetic data of H- and Z-component with time resolution of one minut e from each 11 stations nearby 100 degrees E GM and 300 degrees E GM meridi ans are used to analyze the effect of magnetospheric disturbance on geomagn etic features of the auroral electrojet and disturbed currents in mid- and low-latitude ionospheres during a magnetic storm on April 16-17, 1994. It i s shown that the geomagnetic response of the magnetosphere -ionosphere coup ling is related to the local time zone of the station. This is caused by th e combined effects of the magnetospheric convection pattern and the field-a ligned current systems. During a magnetic storm, genarally speaking, the va riation of the westward auroral electrojet is the stronger one, and the aur oral region may expand both poleward and equatorward. Besides, the center b elt of the electrojet will move toward lower latitude. At the mid-latitude ionosphere the establishment of the region 2 field-aligned current will shi eld the disturbance caused by the region 1 field-aligned current and produc e a reversed current leading to a reversed geomagnetic field. These may cau se a short time increasing of a eastward electric field at night side. As a result, the simultaneously h' F (minimum vertual height for F-region) enha ncement due to the E X B drift effect will be observed at several stations nearby a meridian. On the other hand, variations of geomagnetic field near the equator area are mainly influenced by the ring current and the ionosphe ric equatorial electrojet.