Explicit IMF By‐Effect Maximizes at Subauroral Latitudes (Dedicated to the Memory of Eigil Friis‐Christensen)

Abstract

AbstractThe most important parameter in the coupling between solar wind and geomagnetic activity is the Bz‐component of the interplanetary magnetic field (IMF). However, recent studies have shown that IMF By is an additional, independent driver of geomagnetic activity. We use here local geomagnetic indices from a large network of magnetic stations to study how IMF By affects geomagnetic activity at different latitudes for all solar wind and, separately, during coronal mass ejections. We show that geomagnetic activity, for all solar wind, is 20% stronger for By > 0 than for By < 0 at subauroral latitudes of about 60° corrected geomagnetic latitude. During coronal mass ejections, the By‐effect is larger, about 40%, at slightly lower latitudes of about 57° (corrected geomagnetic) latitude. These results highlight the importance of the IMF By‐component for space weather at different latitudes and must be taken into account in space weather modeling.