M. O. Fillingim, J. S. Halekas, and R. P. Lin,
Space Sciences Laboratory, University of California, Berkeley
Presented at the 2006 AGU Fall Meeting, San Francisco, CA, December 11 - 15, 2006
In the high latitude magnetotail, the solid body of the Moon acts as a particle absorber of interplanetary electrons traveling Earthward creating a lunar shadow in the electron flux. Electrons that are just outside the lunar shadow mirror nearer Earth and return to the vicinity of the Moon deflected by the cross tail convection electric field. By measuring this displacement from lunar orbiting spacecraft, the convection electric field can be determined. The convection electric field is an important parameter for magnetospheric dynamics but is difficult to accurately measure by other means. Pioneering work measuring the convection electric field from lunar orbit done during the Apollo Era will be reviewed. We revisit this problem using data from Lunar Prospector which had better energy, angular, and temporal resolutions. Out initial results show that at times the high latitude convection velocity is stable and on the order of 10 km/s in the equatorward direction corresponding to a dawn-dusk electric field of 0.1 mV/m, close to expectations. At other times no consistent electric field can be determined from the data either due to noise, spatial or temporal variability, or another breakdown in the assumptions that go into this method. We will present more detailed analyses of several events with consistent and non-consistent electric fields. Reasons for discrepant cases will be discussed. Finally, we discuss more ideal detector designs and orbit configurations to address this problem for future lunar missions.
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