Effect of the dawn‐dusk interplanetary magnetic field By on the field‐aligned current system

Abstract

A constant dawn‐dusk By component is set as an interplanetary magnetic field (IMF) condition in our global MHD simulations to investigate the effects of IMF By on the closure of the field‐aligned current (FAC) in the magnetosphere. On the basis of the steady state magnetosphere results, we trace streamlines of FAC from the ionosphere to draw the global geometry of current streamlines in the magnetosphere. Unlike those cases in which the IMF is purely northward or southward, the introduction of the dominant IMF By significantly changes the topologies of the current streamlines. Cusp and mantle currents arise, and the symmetry of the FAC across the noon‐night meridional plane breaks in the ionosphere. In addition to the self‐closed currents in the Northern or Southern hemispheres, three more types of current streamlines connecting the two ionospheres are shown from the simulation results. The first current, including the cusp current, originates from the southern ionosphere and flows into the northern ionosphere. The second current, mainly the mantle current, and the tail current are connected to form a single current system, threading most of the magnetosphere along a spiral‐like path and closing through the two lobes in the far magnetotail. The third current flowing out of the southern and into the northern ionosphere connects the two ionospheres by finally closing through the bow shock instead of the magnetopause. Quantitative results are presented and discussed for the four types of current streamlines and indicate that for the dominant IMF By conditions the bow shock current should be included among the magnetosphere‐ionosphere current system.