Key features of >30 keV electron precipitation during high speed solar wind streams: A superposed epoch analysis

Abstract

We present an epoch analysis of energetic (>30keV) electron precipitation during 173 high speed solar wind streams (HSS) using riometer observations of cosmic noise absorption (CNA) as a proxy for the precipitation. The arrival of the co-rotating interaction region (CIR) prior to stream onset, elevates the precipitation which then peaks some 12h after stream arrival. Precipitation continues for several days following the HSS arrival. The MLT distribution of CNA is generally consistent with the statistical pattern explained via the substorm process, though the statistical deep minimum of CNA/precipitation does change during the HSS suggesting increased precipitation in the 15-20 MLT sector. The level of precipitation is strongly controlled by the average state of the IMF BZ component on the day prior to the arrival of the stream interface. An average negative IMF BZ will produce higher CNA across all L-shells and MLT, up to 100% higher than an average positive IMF BZ. © 2012 American Geophysical Union. All Rights Reserved.