Explaining the cause of asymmetry in the electron foreshock

Abstract

As the solar wind nears the edge of Earth's magnetosphere, it creates a bow shock, a region in which the solar wind speed drops abruptly. Some solar wind electrons bounce off the bow shock; these reflected electrons interact with oncoming solar wind in a region known as the electron foreshock. In the electron foreshock the reflected electrons generate plasma wave activity that results in radio wave emission. A new study shows that the sunward and antisunward wings of this electron foreshock differ. Analyzing wave and electron measurements from the Wind spacecraft, Pulupa et al. show that the asymmetry is due to the strahl, a beam of high‐velocity electrons that is a component of the solar wind. Strahl electrons bounce off the bow shock only into the sunward wing of the foreshock, and this asymmetry leads to enhanced plasma wave activity in the sunward wing. (Geophysical Research Letters, doi:10.1029/ 2011GL048029, 2011)