The dayside diffuse aurora brightening/dimming that associated with Magnetosheath High-Speed-Jets and their related magnetospheric signatures

Abstract:

Magnetosheath high speed jets (HSJs) are dayside transient disturbances with high speed velocity and large dynamic pressure. They are observed to be associated with significant magnetopause perturbations, irregular pulsations in the magnetosphere, and localized flow enhancements in the ionosphere. On the other hand, large dynamic pressure increases that hit the dayside magnetopause, especially with an interplanetary shock, are observed to cause global disturbances in the dayside magnetosphere, affecting the formation of dayside diffuse aurora. However, whether the transient and localized HSJs can also affect the aurora is still an open question. In this study, 13 HSJ events that identified by THEMIS satellites located within ±1 MLT of the center FOV of the south-pole station all sky imager (ASI). In 9 of those, the HSJs are observed to have a nearly one-to-one relationship with each localized diffuse auroral brightening/dimming. Thus, the 2D observations from south-pole station ASI also have an opportunity to measure the size and motion of HSJs. The result shows that the HSJ-related diffuse aurora signatures are ~0.3-1.5 MLT in azimuthal direction, which is consistent with the cross-sectional diameter of geo-effective HSJs (~1.5-2 Re or ~0.6 MLT). And most of those aurora signatures have poleward and/or azimuthally motion. This is the first time to show the connection between magnetosheath HSJs and diffuse auroras. Furthermore, compression/ULF signatures are observed in the magnetosphere simultaneously within ±3 MLTs of the HSJs. Also, magnetometer data gives 2D perspectives of the related ULF wave propagation.