Simulating Mars Boundary Layer Clouds and Precipitation Observed by the Lidar on Phoenix

Introduction: The LIDAR instrument on the Phoenix mission uniquely observed water ice clouds that form and precipitate within the nighttime residual Planetary Boundary Layer (PBL) on Mars [Whiteway et al., 2008, 2009; Dickinson et al. 2010]. We apply a microphysical model for Mars dust and ice clouds driven by a model of the planetary boundary layer (PBL) for the interpretation of these measurements [Daerden et al. 2010]. This combined model approach simulates nighttime clouds and fall streaks within the PBL that are similar in structure to the LIDAR observations. The precipitating ice crystals are predicted to be very large (30–50 mm effective radius), resulting in downward transport of water vapor within the PBL. In combination with strong daytime mixing this process forms a local closed water cycle which acts to confine water vapor within the PBL.