Presentation #401.08 in the session Titan: Up High, Down Low.
Early in the Cassini mission, the Visible and Infrared Mapping Spectrometer (VIMS) found evidence for an extensive cloud north of 50o latitude and near the altitude of the tropopause. This cloud feature remained observable from 2004 to 2009, when the northern hemisphere emerged from winter and the Hadley circulation (previously downward at the north pole) changed direction at equinox. While not spectroscopically identified, the altitude of the cloud as well as the derived particle sizes point to ethane as the primary constituent. The Community Aerosol and Radiation Model for Atmospheres (CARMA) has previously been used to model clouds of ethane, mixed methane and ethane, and other individual trace hydrocarbon and nitrile species in Titan’s troposphere and stratosphere for various latitudes. Here we concentrate primarily on ethane in the north polar region for the period over which the cloud was observed. CARMA is a column microphysics model that simulates nucleation, condensation, and evaporation of cloud particles as well as particle interaction through coagulation and vertical transport. Ethane cloud particles are found to grow larger (radii ~few microns) than other hydrocarbons in Titan’s atmosphere (except methane). Additionally, ethane can nucleate onto haze particles which have previously been coated by ices from other trace species, enhancing to the composition of the observed cloud. Simulations will be shown to place physical constraints on the size of the ethane particles, their vertical extent, and mass of other hydrocarbon and nitrile ices present.