Small-Scale Aurora Associated With Magnetospheric Flow Vortices After a Solar Wind Dynamic Pressure Decrease

Abstract

Sudden changes of the solar wind dynamic pressure have significant impacts on the dynamics of the magnetosphere-ionosphere system. On 18 February 2011, a sudden decrease in solar wind dynamic pressure was observed by the Wind satellite, which drove the entire magnetosphere-ionosphere system as recorded in many ground-based and space-based measurements. In the magnetosphere, Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft observed a counterclockwise plasma flow vortex propagating tailward. Near the magnetic footprints of the THEMIS spacecraft, the ground magnetometers observed magnetic field variations that corresponded to a counterclockwise vortex in the equivalent ionospheric currents, which in turn indicated the presence of upward field-aligned currents. The all-sky imager at RANK station near the THEMIS footprints also observed a simultaneous enhancement of the auroral brightness. Therefore, this comprehensive case study demonstrates a causal chain that links the solar wind dynamic pressure variations to magnetospheric, ionospheric, and auroral activities.