Earth Planets Space, Vol. 64 (No. 2), pp. 237-245, 2012
M. Holmström, S. Fatemi, Y. Futaana, and H. Nilsson
Swedish Institute of Space Physics, PO Box 812, SE-98128 Kiruna, Sweden
(Received February 10, 2011; Revised June 10, 2011; Accepted June 20, 2011; Online published March 8, 2012)
We study the interaction between the Moon and the solar wind using a three-dimensional hybrid plasma solver. The proton fluxes and electromagnetical fields are presented for typical solar wind conditions with different magnetic field directions. We find two different wake structures for an interplanetary magnetic field that is perpendicular to the solar wind flow, and for one that is parallell to the flow. The wake for intermediate magnetic field directions will be a mix of these two extreme conditions. Several features are consistent with a fluid interaction, e.g., the presence of a rarefaction cone, and an increased magnetic field in the wake. There are however several kinetic features of the interaction. We find kinks in the magnetic field at the wake boundary. There are also density and magnetic field variations in the far wake, maybe from an ion beam instability related to the wake refill. The results are compared to observations by the WIND spacecraft during a wake crossing. The model magnetic field and ion velocities are in agreement with the measurements. The density and the electron temperature in the central wake are not as well captured by the model, probably from the lack of electron physics in the hybrid model.
Key words: Moon, solar wind, hybrid model, plasma.