Association of Equatorward Extended Auroral Streamers With Overshielding Conditions at Equatorial Latitudes: First Observations

We report the first observations of the association between equatorward extending streamers and overshielding using the THEMIS all-sky imagers and ground magnetometers. Because auroral streamers indicate plasma sheet flow bursts, these observations uncover the effect of flow bursts on overshielding. Results show that, in general, bright equatorward extended streamers were associated with an increase in equatorial electrojet (EEJ) on the nightside and a decrease in the dayside EEJ, indicating a striking correspondence between auroral streamers and overshielding conditions. Thus, the driving of overshielding at equatorial latitudes can be identified via bright equatorward extended streamers, indicating that flow bursts are an alternate means to discern the earthward injections that increase the region 2 field aligned currents and associated overshielding electric fields. Repetitive auroral streamers were associated with repetitive overshielding, resulting in a stepwise development of the dayside and nightside EEJ. The stepwise intensifications were also observed in the midlatitude positive bay and Pi2 pulsations. Our results could explain the occurrence of overshielding conditions at equatorial latitudes during substorms and nonsubstorm times without a northward turning of IMF-Bz. As seen through streamers, the localized current structures (wedgelets) associated with flow bursts giving injection that leads to overshielding is titled northeast-to-southwest. Our results add a new element to the understanding of high-to-low latitude electrodynamical coupling by demonstrating the association between bright equatorward extended auroral streamers and enhanced shielding electric fields caused by earthward injections associated with flow bursts.