Cloud formation under Mars Pathfinder conditions

Temperature data taken during the Mars Pathfinder entry are applied to a ti me dependent microphysical model of cloud formation. Our goal is to reprodu ce the characteristics of clouds observed at the Pathfinder site. We assume that the total water column abundance is 11 percipitable microns. We also assume that the atmospheric dust initially has a lognormal size distributio n with a modal radius of 0.6 mu m, r(eff) = 15 mu m, and an optical depth o f tau = 0.5. Three temperature profiles are used in the model calculations. The first is the Pathfinder entry observation. The second is this same pro file but with the inversion at 10 km removed. The third simulation uses the temperature profiles calculated by the Ames Mars general circulation model for Mars Pathfinder conditions. In all cases clouds form at altitudes of 3 5-45 km. In addition lower thicker clouds form within the 10 km inversion O f the unaltered profile, while peak cloud formation occurred near local noo n at 20 km for the GCM calculated profiles. Given a combination of all thre e temperature scenarios, cloud optical depths, particle sizes, and colors a re consistent with IMP observations.