Field-Aligned Current Dynamics and Its Dependence on Solar Wind Conditions

Field-aligned currents (FACs) are the currents flowing into and out of the ionosphere which connect to themagnetosphere. They provide an essential linkage between the solarwind-magnetosphere system and the ionosphere, and the understanding of these currents is important for global magnetosphere dynamics and space weather prediction. The three spacecraft ST5 constellation provides an unprecedented opportunity to study in situ FAC dynamics in time scales that can not be achieved by earlier studies with single spacecraft studies or large-spaced conjugate spacecraft studies. In this study, we use the magnetic field observations during the whole ST5 mission to study the dependence of FAC dynamics on solar wind conditions. FAC peak current densities show very good correlations with some solar wind parameters, including IMF Bz, dynamic pressure, Ey, and some IMF angles, but not with other parameters. Instant FAC speeds show generally much weaker dependence on solar wind conditions comparing to FAC peak current densities. This obvious dislinkage between FAC peak current densities and speeds implies that FAC peak current densities are more controlled by solar wind conditions, while FAC speeds are more strongly controlled by internal magnetosphere-ionosphere processes which can not be substantially representated by the conventional solar wind parameters tested in this study.