The lowest possible latitude of the westward electrojet during severely disturbed periods

It has been reported that the AE index cannot, at times, adequately monitor the auroral electrojets because as magnetic activity increases, it shifts equatorward from the standard AE stations, resulting in a serious underestimation of the auroral electrojet intensity. To evaluate quantitatively the equatorial shift of the westward electrojet, an extensive database obtained from CANOPUS, Alaska and IMAGE chains of magnetometers are utilized in this study. The data thus assembled enable us to determine how the westward electrojet shifts equatorward with increased magnetic activity. We are particularly interested in the latitude of the center of the westward electrojet during intense magnetic storms. The tendency of equatorward shift is confirmed from this study. However, the peak of the westward electrojet seems to shift only approximately 60 degrees in magnetic latitude, regardless of magnetic activity levels. Therefore the current AE network, which covers as low as about 62 degrees, does not have any serious problems in monitoring the auroral electrojet. The relative location of the westward electrojet with respect to the global auroral image taken from the Polar satellite is also examined. It is found that the center of the westward electrojet does not flow over the brightest auroral region but slightly poleward of it, with less luminous region. It indicates that the electric field is more important in intensifying the auroral electrojet than the ionospheric conductivity.