On the MLT distribution of F region polar cap patches at night

Abstract

Eight years of meridian scanning photometer data from Ny-Alesund, Svalbard have been analyzed to study the occurrence of F region polar cap patches at night. In total 333 patches in 43 days were observed to hit the poleward boundary of nighttime auroras which is a unique signature of ongoing tail reconnection. The MLT distribution of patches is smooth and exhibit a bell shaped function symmetric around 23:25 MLT. The symmetry of the patch distribution about midnight indicates that patches populate the morning cell and the dusk cell of polar cap convection at the same probability. About 60% of the patches exit the polar cap from 22-01 MLT, but the entire distribution span from 18:30-04:50 MLT, i.e., nearly the full MLT span where tail reconnection may occur. The patch occurrence statistics presented here is an important new result of relevance to phenomena related to the presence and transport of patches. Copyright 2007 by the American Geophysical Union.