Solar Wind-Lunar Magnetic Anomaly Interaction: Hybrid Model Simulations

The localized, crustal magnetic field on the Moon shows a complex interaction with the impinging solar wind. The interaction includes interesting and unique plasma physics processes when a small magnetosphere-like field structure, commonly referred to as a mini-magnetosphere, is formed above the magnetic anomaly. Because of the small size of the interaction region, kinetic effects play an important role in the interaction region. Recently, unique new particle and field data have been obtained above the lunar magnetic anomalies by the Chandrayaan-1 and Kaguya missions. In this work, we model a lunar magnetic anomaly in the spatial scale of hundreds of kilometers with an 100nT surface field anomaly. We employ the 3D HYB hybrid plasma model (HYB-Anomaly) developed at the Finnish Meteorological Institute, in which ions are treated as fully kinetic macroparticles, with electrons providing a massless, charge-neutralizing fluid. We study the properties of particles and fields within the mini-magnetosphere, especially, characteristic features of the electric field resulting from the different motion of protons and electrons. We also analyze the response of the mini-magnetosphere to the upstream solar wind parameters, such as the direction of the interplanetary magnetic field. Finally, Chandrayaan-1 particle observations are used for comparison.