An investigation of possible causes of the holes in the condensational Venus cloud using a microphysical cloud model with a radiative-dynamical feedback

Near-infrared observations of the nightside of Venus reveal regions of high brightness temperatures. These regions of high brightness temperatures are caused by the localized evaporation of the middle and lower cloud decks, which are about 50 to 60 km above the surface of the planet. We simulate the Venus condensational middle and lower cloud deck with the University of Colorado/NASA Ames Community Aerosol and Radiation Model for Atmospheres (CARMA). Our simulated clouds have similar characteristics to the observed Venus clouds. Our radiative transfer model reproduces the observed temperature structure and atmospheric stability structure within the middle cloud region. A radiative-dynamical feedback occurs which generates mixing due to increased absorption of upwelling infrared radiation within the lower cloud region, as previously suggested by others. We find that localized variations in temperature structure or in sub-grid scale mixing cannot directly explain the longevity and optical depth of the clouds. However, vertical motions are capable of altering the cloud optical depth by a sufficient magnitude in a short enough timescale to be responsible for the observed clearings. (C) 2007 Elsevier Inc. All rights reserved.