Explicit IMF B-y-Effect Maximizes at Subauroral Latitudes (Dedicated to the Memory of Eigil Friis-Christensen)

摘要

The most important parameter in the coupling between solar wind and geomagnetic activity is the B-z-component of the interplanetary magnetic field (IMF). However, recent studies have shown that IMF B-y 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 B-y 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 B-y > 0 than for B-y < 0 at subauroral latitudes of about 60 degrees corrected geomagnetic latitude. During coronal mass ejections, the B-y-effect is larger, about 40, at slightly lower latitudes of about 57 degrees (corrected geomagnetic) latitude. These results highlight the importance of the IMF B-y-component for space weather at different latitudes and must be taken into account in space weather modeling.