Abstract
Velocity distribution of the solar wind electrons that penetrate through the lunar wake boundary is investigated by calculating orbits of the electrons injected into model structures of layers of electric fields. Only the electrons with sufficient energy to overcome the potential difference penetrate through the wake boundary. The electrons injected along the magnetic field lines which intersect the model structure undergo pitch angle scattering due to electric field component perpendicular to the magnetic field. After the passage through the electric field, the electrons have significant perpendicular component of velocity as well as the parallel component larger than a lower limit, which is dependent on the electric potential of the wake boundary. The velocity distribution can account for the cyclotron resonance with sunward-propagating whistler mode waves that were detected by GEOTAIL at 27 lunar radii upstream of the moon on October 25, 1994.
