Global auroral response to interplanetary media with emphasis on solar wind dynamic pressure enhancements

Abstract

This paper reviews some important progress made on large-scale auroral dynamics under a variety of interplanetary conditions with emphasis on solar wind dynamic pressure increases. In the last decade, the availability of high time and spatial resolution far-ultraviolet auroral images from Polar has allowed such work to be performed statistically. Like geomagnetic disturbances, the southward component of interplanetary magnetic fields (IMFs) and the solar wind velocity are the major contributors to the hemispheric auroral power through magnetic merging/ reconnection and solar wind viscous processes, respectively. Global auroral imaging from Polar has also demonstrated the importance of sudden increases in the solar wind dynamic pressure. When the magnetosphere is compressed, auroral transients (<10-20 min) are produced first on the dayside and then on the nightside of the oval. The dayside auroral transient is associated mainly with enhancements in both energy and energy flux of precipitating electrons from the plasma sheet. On the nightside the compression-induced aurora is more intense, especially during southward IMF, and often leads to widening of the oval and the closure of the polar cap. Observations seem to suggest an increased efficiency in the solar wind-magnetosphere coupling and an enhancement in the convection-related DP 2 current system by shocks, but whether or not the magnetospheric compression can enhance dayside merging/nightside reconnection and/or viscous processes remains uncertain. To evaluate the importance of magnetospheric compression on large-scale aurora, 27 co-rotating interaction region (CIR) events, which are an important source of high solar wind plasma density in the solar wind, are studied. A superposed epoch analysis of the solar wind plasma data and auroral power during the 27 CIR events indicates a modest increase (80%) in the global auroral power across the CIRs. Global auroral power is also more intense in a high-speed stream than in a low-speed stream. When these results and a high recurrent rate are combined, the CIR and its high-speed downstream region are an important interplanetary event that can exert a profound impact on the auroral ionosphere.