A Meandering Lunar Wake Produced by the Pickup of Reflected Solar‐Wind Ions

Abstract

The lunar wake is a global disturbance generated when the Moon interacts with the incident solar-wind (Halekas et al., 2015). It is characterized by the solar-wind plasma depletion behind the Moon, which arises from plasma absorption on the Moon's dayside surface (Lyon et al., 1967). The Moon lacks a significant atmosphere/ ionosphere and a non-negligible global magnetic field, and most of the incident solar-wind directly impacts its surface, thereby being absorbed (Saito et al., 2008). An ensuing global magnetic disturbance appears in the wake (Ness et al., 1967). The magnetic field can increase by 20%-30% in the central wake, but decreases in the surroundings (Xie et al., 2013;Zhang et al., 2014). The strength and the global pattern of these magnetic perturbations strongly depend on the solar-wind plasma beta and the interplanetary magnetic field (IMF) orientation, indicating that they are diamagnetic effect arising from plasma pressure gradient across the plasma depletion boundary (