Association of Equatorward Extending Auroral Streamers With Ground Magnetic Perturbations and Geosynchronous Injections

Auroral streamers have been found to be a particularly important cause of magnetic perturbations within the auroral oval during substorms. We present a detailed investigation on the association of equatorward extending auroral streamers with ground magnetic perturbations at locations initially equatorward of the auroral oval using Time History of Events and Macroscale Interactions imagers and ground magnetometers. Based on the analysis of four events, we show that negative perturbations in the horizontal (H) component at initially subauroral latitudes were not seen prior to streamer onset, and the peak negative H‐bay at subauroral latitudes coincided with the equatorward extending auroral streamers. Although stations close to the poleward boundary of auroral oval showed modest H‐component perturbations in response to the substorm onset and poleward auroral intensifications, the abrupt and large responses within the oval were associated with the onset of streamers. Results confirm that ground magnetic perturbations that are traditionally perceived as signatures of magnetic substorm onset are not always an auroral substorm onset but can also be related to auroral streamers. These results are supported by the remarkable correlation of positive bay onset and sudden Pi2 enhancement with the onset of auroral streamers, irrespective of the classical substorm onset. In addition, the magnitude of positive bay and amplitude of Pi2 pulsations, particularly at subauroral latitudes, are enhanced during the events of equatorward extending streamers. In general, all streamer events were accompanied by dipolarization and electron flux enhancement at geosynchronous orbit that continue to strengthen during the emergence of bright streamers. Plain Language Summary Large, rapid perturbations in the ground magnetic field at high latitudes have been considered a major space weather hazard as they can harm technological systems. Such magnetic perturbations are common at auroral latitudes during geomagnetic storms and substorms. However, it is a matter of research to comprehend under what conditions such perturbations can extend equatorward of the auroral oval. The ground magnetic perturbations at auroral latitudes are shown to be linked with auroral streamers. Auroral streamers are roughly north‐south oriented narrow bands of auroral luminosity. They originate near the poleward edge of the auroral oval and propagate equatorward. Auroral streamers are related to flow bursts in th