Cloud formation under Mars Pathfinder conditions

Temperature data taken during the Mars Pathfinder entry are applied to a time dependent microphysical model of cloud formation. Our goal is to reproduce 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 distribution with a modal radius of 0.6 μm, r eff =1.5 μm, and an optical depth of τ = 0.5. Three temperature profiles are used in the model calculations. The first is the Pathfinder entry observation. The second is this same profile 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 35–45 km. In addition lower thicker clouds form within the 10 km inversion of the unaltered profile, while peak cloud formation occurred near local noon at 20 km for the GCM calculated profiles. Given a combination of all three temperature scenarios, cloud optical depths, particle sizes, and colors are consistent with IMP observations.