The influence of IMF cone angle on invariant latitudes of polar region footprints of FACs in the magnetotail: Cluster observation

Abstract:

In solar wind-magnetosphere-ionosphere interactions, the large scale FACs play a crucial role in transferring the solar wind momentum and energy to magnetosphere and ionosphere. The interplanetary parameters affect the energy transfer process and the associated FACs directly. The FACs in the Plasma Sheet Boundary Layers (PSBLs) connected with those in the polar region through the magnetic field lines and they are important for the energy flows in the solar wind-magnetosphere-ionosphere system. How the solar wind affects the large scale FACs from the magnetotail to the polar region is still an open question. And no study on the relationship between the IMF cone angle and the invariant latitudes of the FACs in the PSBLs in the magnetotail has been done. This study is focused on the influence of the IMF cone angle θ (the angle between the IMF direction and the Sun-Earth line) on the projection locations of the observed FACs by Cluster in the northern PSBL in the magnetotail. We performed a statistic study of 542 FAC cases observed by the four Cluster spacecraft in the northern hemisphere. The results show that the large FAC (>10 nA/m²) cases occur at the low ILATs (<71 º) and mainly occur when the IMF cone angle θ>60º, which implies the footprints of the large FACs mainly expand equatorward with large IMF cone angle. The equatorward (poleward) boundary of the FAC footprints decreases (increases) with the IMF cone angle. The equatorward boundary is more responsive to the IMF cone angle. This is the first time a correlation between FAC projected location and IMF cone angle has been determined.