Erika Barth (SWRI) - Cloud Microphysics and Convection in Titan's Atmosphere
Date Time Location
November 23rd, 2009 12:00pm-1:00pm 54-915
Erika Barth
Southwest Research Institute
Title: Cloud Microphysics and Convection in Titan's Atmosphere
Host: Angela Zalucha
Abstract: It is now well established that clouds form in Titan's atmosphere. Polar clouds existed as a prominent feature in the southern
hemisphere for a number of years. Mid-latitude clouds, clustered near 40 deg. S latitude, have been observed by both the
Cassini spacecraft and ground-based telescopes. At the Huygens landing site, about 10 deg. S of the equator, optically thin
condensate layers were observed in the mid to lower troposphere. The rapid lifetimes and common heights of the South Pole and
mid-latitude clouds, in particular, point to a convective origin. To understand the conditions necessary for convective clouds
to form in Titan's atmosphere, we have developed the Titan Regional Atmospheric Modeling System. TRAMS is a three-dimensional,
time-dependent, coupled fully compressible dynamic and microphysical model capable of simulating methane and ethane clouds. I
will discuss a number of simulations, which have shown that the types and observable properties of the clouds able to form in
Titan's atmosphere are strongly tied to the amount of methane present. For example, for cloud tops to reach the tropopause
requires a surface humidity of greater than 60%, whereas cloud tops below 30 km occur for only 50% humidity. The amount
Convective Available Potential Energy (CAPE) at the Huygens landing site is insufficient for optically thick convective clouds
to form. The appearance of convective clouds at the South Pole and mid-latitudes then points to a more humid environment.