Solar wind control of ionospheric equivalent currents and their time derivatives

A solid understanding of the solar wind control of ground magnetic field disturbances is essential for utilizing the existing long time series of ground data to obtain information on solar wind-magnetosphere-ionosphere coupling. We have used 20 years of International Monitor for Auroral Geomagnetic Effects magnetometer data (54°-76° magnetic latitude) to study the solar wind control of the ionospheric equivalent current density and its time derivative (<|dJ_eq/dt|>). We found that <|dJ_eq/dt|> peaks at the premidnight and prenoon ends of the westward electrojet. The prenoon <|dJ_eq/dt|> peak was most intense during fast solar wind and radial interplanetary magnetic field (IMF). The location of the peak was not affected by the IMF orientation but persisted at 8-10 magnetic local time and 70°-75° latitude, near the boundary between the westward and eastward electrojets. Sensitivity of this boundary to disturbances was suggested as a possible explanation for the persistent prenoon location of the peak. The premidnight peak was most intense during southward IMF orientation. While faster solar wind mainly resulted in more intense <|dJ_eq/dt|> in the premidnight sector, stronger IMF caused the region of intense <|dJ_eq/dt|> to spread to the postmidnight, dawn, and dusk sectors. A good correspondence was found between development of the nightside <|dJ_eq/dt|> intensification and average substorm bulge and oval aurora as determined by Gjerloev et al. (2007). The bulge aurora covered the western end of the westward electrojet where the equivalent current also had a significant poleward component. The substorm oval aurora, on the other hand, extended eastward along the westward electrojet.