The Polarity of IMF By Strongly Modulates Particle Precipitation During High‐Speed Streams

Abstract

Abstract Recent studies have suggested that the interplanetary magnetic field (IMF) By component modulates particle precipitation during solstices, or periods of high dipole tilt Ψ. So far this explicit IMF By‐effect has only been shown in statistical studies. Here we analyzed a sequence of high‐speed stream (HSS) driven events of auroral (30 keV and >100 keV) particle precipitation. We show that when HSSs are comparable in terms of IMF and solar wind parameters, they can lead to systematically stronger particle precipitation in individual events when the signs of By and Ψ are opposite. We also perform a superposed epoch analysis of 485 HSSs giving further evidence that the By‐effect is especially significant during HSSs. This is likely due to the persistent IMF By polarity during HSSs. We show evidence that the By dependence in particle precipitation is caused by a similar By dependence in substorm occurrence.

Keywords

• electron precipitation
• solar wind‐magnetosphere coupling
• magnetospheric dynamics
• high‐speed streams