Large-scale structures in the Polar Rain

We present two distinctive spatial structures (similar to 140 and similar to 1000km) in the polar rain electron energy fluxes observed by Defense Meteorological Satellite Program satellites. The 16 May 2005 event indicates that sources of the similar to 1000km structures were not in the solar wind electrons. Statistical analysis of 239 events shows that the similar to 1000km structures were associated with high solar wind speed and density while the similar to 140km structures did not depend on solar wind conditions. The structures are about 5 and 0.7 R-E when mapped to the magnetopause and comparable to the typical Kelvin-Helmholtz (KH) wavelengths (3-14 R-E) and flux transfer event (FTE) sizes (similar to 0.6-1.3 R-E) on the magnetopause. Our calculations indicate that the KH waves are unstable under the high solar wind speed and density. The observations and calculations suggest that the similar to 1000km and similar to 140km structures are likely caused by the KH waves and FTE on the magnetopause.