Diffuse Auroral Patches induced by Upstream Dynamic Pressure Enhancements of the Bow Shock

Diffuse auroral patches on the dayside are considered as signatures of magnetospheric compressions. However, whether and how these signatures of the diffuse aurora patches are modulated by the upstream sources have not been statistically investigated in previous studies. In this study, we identified 51 dayside diffuse auroral patches and examined their two-dimensional evolutions by using the Time History of Events and Macroscale Interactions during Substorms probes and the ground-based all-sky imager at the South Pole. Two typical events show diffuse auroral patches associated with upstream dynamic pressure enhancements of the bow shock and magnetospheric compressions, followed by their east-west propagations. The statistical results suggest that most conjunction events were associated with foreshock activities, while the remaining events were associated with dynamic pressure enhancements in the pristine solar wind. These azimuthal motions can be either eastward or westward, with initial locations at ∼12-13 and ∼9-10 Magnetic Local Time, respectively, exhibiting a dawn-dusk asymmetry. Additionally, poleward motions were found in all events. Larger dynamic pressure enhancements correspond to faster poleward motions and could push the initial diffuse auroral brightening toward lower latitudes. These characteristics of their poleward motions were consistent with the Tamao path.