IMF By influence on fast earthward convection flows in the near-lunar magnetotail

We statistically investigate convective earthward fast flows (V_⊥ > 200 km/s) using data measured by the Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon’s Interaction with the Sun (ARTEMIS) mission in the tail plasma sheet during 2011-2022. Statistical results show that under the penetration and induction of the dusk-dawn interplanetary magnetic field component (IMF B_y), the magnetotail B_y aligned with the direction of IMF B_y on average dominates the entire investigated near-lunar tail plasma sheet region, regardless of the hemisphere. Compared with the statistical results of the near-Earth magnetotail, IMF B_y has a greater impact on the near-lunar magnetotail (the span of influence is greater). The influence of IMF B_y on magnetotail B_y may have a dusk-dawn asymmetry characteristic, with a weaker influence in the premidnight compared to the postmidnight. In addition, we find that the impact of IMF B_y on earthward perpendicular fast flows exhibits interhemispheric asymmetry in average V_⊥y and it is highly correlated with the direction of magnetotail B_y. In more than 80% of the data bins, both tail B_y and V_⊥y are in their dominating directions. In those bins where the V⊥y direction is opposite to the dominating direction, only slightly more than 50% of the bins have tail B_y in the direction opposite to the dominating tail B_y. Based on the statistical results, we infer that nonzero IMF B_y conditions affect the magnetotail and fast earthward convection at lunar distances. However, occasionally local dynamics can have a significant impact on magnetotail B_y and V_⊥y, even overriding the influence of IMF B_y, which has been observed before at near-Earth distances.