LAUSR

Abstract Polar cap patches are common irregularities in the polar ionosphere, where their formation and evolution can directly affect satellite navigations and communications as well as over-the-horizon radar observations, etc. However, affected by the various dynamic processes during the solar wind-magnetosphere-ionosphere coupling, there is no fully accepted formation mechanism of polar cap patches. In this paper, a statistical analysis of 345 patches at the dayside sectors during 09:00–15:00 magnetic local time (MLT), observed by EISCAT Svalbard Radar (ESR) 42 m antenna from 2010 to 2013, has been performed. The dependence of their occurrence on solar wind and interplanetary magnetic field (IMF) conditions as well as their MLT distribution has been statistically investigated. The results show that the polar cap patches are preferentially formed during southward IMF conditions. In particular, the MLT dependence of the patches presents a clear IMF By-related prenoon-postnoon asymmetry, suggesting the patch formation is clearly modulated by the IMF By polarity. Moreover, our statistical results indicate that the patches should not be caused by the variations of the solar wind dynamic pressure or the solar wind velocity. All the results indicate that the pulsed dayside magnetic reconnection is possibly a significant formation mechanism of polar cap patches.