Particle Precipitation Driven by Solar Wind Dynamic Pressure Variations

The global auroral response to interplanetary shocks has been studied and reported. The transient behavior of the aurora often reported by previous workers suggests a cause-and-effect relationship between the shock front and the auroral transient. However, it is less known if the high solar wind dynamic pressure down stream of a shock can have significant effects on the global auroral morphology. In this report we present an observational study of the auroral response to a large solar wind dynamic pressure. We use global auroral images acquired by the ultraviolet imager onboard the Polar spacecraft and solar wind and interplanetary magnetic field data from the Wind spacecraft. From a limited number of events, it is found that the luminosity of aurora indeed showed a general increase even long after sudden impulses. The increase may persist as long as the solar wind dynamic pressure stays high and may disappear within ~10 minutes after the dynamic pressure drops. A detail examination of the aurora indicates that there exist small temporal structures that can be associated with small perturbations in the solar wind dynamic pressure during the passage of the high solar wind pressure. These results provide strong evidence of auroral precipitation driven directly by the solar wind. We will present the detail result and possible mechanisms.