Nat Gopalswamy (NASA GSFC) and Kalevi Mursula (University of Oulu)
The interaction of the solar wind with the Earth’s magnetic ﬁeld produces geomagnetic activity, which is critically dependent on the orientation of the interplanetary magnetic ﬁeld (IMF). Most solar wind coupling functions quantify this dependence on the IMF orientation with the so-called IMF clock angle in a way, which is symmetric with respect to the sign of the By component. However, recent studies have suggested that IMF By is an additional, independent driver of high-latitude geomagnetic activity, leading to higher (weaker) geomagnetic activity in Northern Hemisphere (NH) winter for By > 0 (By < 0). We quantify the size of this explicit By-eﬀect with respect to the solar wind coupling function, both for northern and southern high-latitude geomagnetic activity. We also show that the By-effect maximizes at subauroral latitudes at about 60 degrees geomagnetic latitude. During the Earth-passage of coronal mass ejections (CMEs), geomagnetic activity is about 40% stronger for By > 0 than for By < 0 at subauroral latitudes. These results highlight the importance of the IMF By-component for space weather and must be taken into account in future space weather modeling.
Mode of presentation: oral (Need to be confirmed by the SOC)