Coordinated THEMIS spacecraft and all‐sky imager observations of interplanetary shock effects on plasma sheet flow bursts, poleward boundary intensifications, and streamers

Abstract

AbstractIn order to characterize plasma sheet and nightside auroral disturbances in response to interplanetary shocks, we have examined three interplanetary shock events that occurred when multiple Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft were located in the plasma sheet near midnight while ground‐based aurora data were available near the spacecraft footprints. Large‐scale responses we found are that the magnetotail magnetic pressure started to increase within ~2 min of the SYM‐H jump, and the diffuse aurora near the auroral equatorward boundary intensified over a wide magnetic local time range, due to the shock compressional effect, on average 3 min after the shock arrival. In addition, we also identified plasma sheet and auroral disturbances that are more transient and localized. Earthward or equatorward flow bursts are observed in the near‐Earth plasma sheet on average 5 min after the SYM‐H increase. We find that these fast flows, originating downtail of the near‐Earth spacecraft, form a localized channel, since only some of the spacecraft detected the flow bursts. Poleward boundary intensifications (PBIs) and subsequent north‐south directed auroral streamers are then formed, while no substorm activity was detected. Those auroral forms are also localized in space near midnight and around the footprint of the spacecraft. These results indicate that the fast flows are azimuthally localized channels and are the magnetotail counterpart of the PBIs and streamers and that such localized disturbances are triggered by the interplanetary shocks in addition to the large‐scale compression of the magnetosphere.