SIMULATIONS OF THE LUNAR SODIUM ATMOSPHERE

A new Monte Carlo type model of the lunar sodium atmosphere has been d eveloped and applied to recent ground-based imaging observations. The model assumes a steady state atmosphere with production of sodium due to a spatially uniform source (e.g., meteor impact vaporization) or a solar zenith angle dependent source (e.g., solar wind sputtering or ph otodesorption). The loss processes included in the model are surface a dsorption and photoionization. Solar radiation pressure is also accoun ted for. The model output is analyzed for overall spatial structure an d compared with recent observations and theory. The results indicate t hat a sodium release mechanism that decreases in source rate with incr easing solar zenith angle is best able to reproduce imaging data taken on September 30, 1991.