Solar wind plasma entry into the magnetosphere under northward IMF conditions

Abstract

This study examines how solar wind plasma enters the magnetosphere under northward interplanetary magnetic field (IMF) conditions, using the Open Geospace General Circulation Model (OpenGGCM) for various solar wind, IMF, and geomagnetic dipole conditions. We trace flow paths of individual fluid elements from the solar wind and study the variation of the topology of the magnetic field line along those flow paths. We find that there is an entry window through which the solar wind plasma can enter the magnetosphere as a result of double high‐latitude reconnection under northward IMF conditions. We investigate how the entry window depends on solar wind, IMF, and geomagnetic dipole parameters, and we estimate the solar wind plasma entry rate for various conditions. We find that the effective entry rate under northward IMF conditions is of the order of 1026 to 1027 particles per second. We also estimate the conditions for which solar wind plasma entry is most efficient. The newly created flux tubes with closed‐field topology are subsequently convected to the nightside and consequently cause magnetosheath plasma to be captured and enter the magnetosphere. Some captured dayside plasma takes about 90 min to convect along the magnetopause to a near tail flank region of the central plasma sheet, thus forming a cold dense plasma sheet. Double high‐latitude reconnection can also release the captured plasma. Thus a balance of inflow and outflow of the captured plasma is eventually established under prolonged northward IMF conditions. We find that high‐latitude reconnection is common under northward IMF conditions in our simulations. It occurs for IMF with any clock angle within [−90°, 90°], measured in front of the bow shock, and for any geomagnetic dipole tilt angle within [−30°, 30°]. An IMF field line with a zero x component usually first reconnects with a geomagnetic field line at the northern high‐latitude boundary when the geomagnetic dipole tilts positive toward the Sun, and vice versa for negative dipole tilt. Our simulations also show that ionosphere conductance affects the convection of the newly closed field lines. Consequently, ionosphere conductance can change the solar wind plasma effective entry rate and can cause asymmetric effective entry rate with respect to positive and negative IMF clock angles.