摘要：The auroral electrojet is enhanced in the polar ionosphere associated with charged particle precipitation and field-aligned currents during substorms. In this paper the geometry of the elctrojet is determined by using the ionospheric equivalent current systems for every 5 minutes during March 18 and 19, 1978. The latitudinal and local time shifts of the oval are examined. Possible relationship of the electrojet oval with expansion of the auroral oval and the field-aligned current belts during substorms are discussed. The electrojet oval in the polar region consists of westward and eastward electrojets, varying with AE index. As the magnetic activity increases, the westward electrojet has distinct latitudinal shifts in different local time sectors: it shifts poleward around the midnight (23:00-03:00 MLT), while moves equatorward in the morning sector (03:00-10:00 MLT) and afternoon sector (20:00-23:00 MLT. The eastward electrojet includes two insulated parts: a higher-latitude part around 80° latitude in the nighttime sector (21:00-03:00 MLT) and a lower-latitude part between 60°–70° latitudes in other local time sectors. As AE index increases, the higher-latitude part of the eastward electrojet expands eastward from 03:00 to 08:00 MLT, while the lower-latitude part shows a equatorward shift in the afternoon sector, which is more or less similar to the westward electrojet.
