Plasma Flow Structure at Lunar Distances

Abstract:

Since 2011, the ARTEMIS 1 and 2 spacecraft have been taking observations in the solar wind and magnetotail as they orbit around the Moon at ~60 Re. With state-of-the-art magnetic field and plasma instruments, they perform the first systematic, two-point observations of the mid-to-distant tail, including an opportunity to study the detailed structure of the mid-to-distant tail. In this study, we study the plasma flow within the magnetotail at -60 Re and its variations in response to the changes in IMF and solar wind. We bin 17 months of 34 single trajectory passes of the ARTEMIS spacecraft to create the vector maps of the plasma flow. After several coordinate transformations, vector maps were constructed on different planes, xy-, xz-, and yz, in aberrated solar wind corrected GSM (aSWGSM) coordinates, and thanks to good orbital coverage of the spacecraft, entire plasma sheet was mapped completely, especially on the dawn side. The dominant flow is tailward. The magnitude of the flow in the xy plane does not change much throughout the width of the magnetotail. The flow components on the yz plane are much smaller than in the xy plane. Deviations from the average pattern are also noteworthy. One of the few localized flow reversals was found to be associated with high speed flows in the solar wind resulting from a CME passage and a strong substorm event. Vector maps are separated with respect to the IMF orientation and compared with MHD model results. Magnetic field patterns corresponding to the flow patterns are also performed and reveal the expected dipolar field topology at -60 Re. We discuss our findings on the general structure and selected special cases from the magnetotail dynamic point of view and in comparison with those from MHD models as well as earlier spacecraft missions.