Heliophysics Science Division
Sciences and Exploration Directorate - NASA's Goddard Space Flight Center

June 29 29, 2018, 1:00 pm - 2:00 pm

June 29nd, 1:00 pm - 2:00 pm

Explicit IMF By-effect in high-latitude geomagnetic activity



Lauri Holappa, 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 the sign of 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). In this paper 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 show that high-latitude geomagnetic activity is significantly (by about 40-50%) stronger for By>0 in NH winter and for By<0 in SH winter. When averaged over all months, high-latitude geomagnetic activity in NH is about 12% stronger for By>0 than for By<0. We also study the latitudinal dependence of the By-effect and show that it is strongest at subauroral latitudes during strong solar wind driving, especially during the Earth-passage of coronal mass ejections (CMEs).