Lunar dayside current in the terrestrial lobe: ARTEMIS observations

Abstract

AbstractWe report Acceleration, Reconnection, Turbulence and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) dual‐probe observations of two events in the terrestrial magnetotail lobe, both characterized by upward moving heavy ions of lunar origin at one of the probes that is magnetically connected with the dayside lunar surface. By treating magnetic measurements at the other probe as the unperturbed lobe fields, we obtain background‐subtracted magnetic perturbations (most significantly in Bz) when the first probe moved in the dawn‐dusk direction across flux tubes magnetically connected to the Moon. These magnetic perturbations indicate the presence of field‐aligned current above the lunar surface. By examining possible carriers of field‐aligned current, we find that lunar heavy ions and accompanying electrons both contribute considerably to the current. Observations of the field‐aligned current also suggest that the charging process at the dayside lunar surface and the associated lobe plasma environment, which have traditionally been viewed as a one‐dimensional current balance problem, are actually more complicated. These observations give the first insights into how heavy ions affect the lunar dayside environment in terms of multispecies plasma dynamics.