New Observations of an Extended Hall Interaction Region Downstream of Lunar Crustal Magnetic Fields

Abstract The lunar surface exhibits small-scale crustal magnetic fields that can give rise to various interactions when subjected to the incident solar wind plasma. These lunar crustal magnetic fields exhibit scale lengths that are much smaller than the typical convected ion gyroradius within the solar wind, leading to an effective demagnetization of the ions. Thus, these lunar crustal magnetic fields provide a natural environment within which Hall electric fields and various current structures may be generated. This study reports observations from THEMIS–ARTEMIS during a periselene of 14 km to the lunar surface and examines the plasma environment within the vicinity of various crustal magnetic fields. The reported observations suggest a Hall interaction region that extends downstream of prominent regions of crustal magnetization. Within these extended interaction regions we report a Hall electric field of 2–3 mV m −1 and oriented upward and sunward, as well as a northward current carried by southward ExB drifting electrons. Lastly, Hall electric fields were observed above the lunar crustal magnetic fields oriented downward and antisunward, as well as parallel currents directed toward the lunar surface, and were consistently observed when the magnetic footpoint was within the cusp region.