Tuesday, 11 February 2003: 1:30 PM
Climate changes in the partitioning of water in convective storms: thermostat or iris? (Invited Presentation)
Two divergent views of the role of deep convective clouds in climate change have been proposed. The thermostat hypothesis asserts that more condensed water will be detrained into cumulonimbus clouds and their associated anvils as climate warms, leading to greater reflection of sunlight and a negative cloud feedback. The adaptive iris hypothesis argues that increasingly efficient precipitation formation in deep convection as climate warms will reduce the water available to form cloud, leading to thinner anvil cirrus and increasing longwave radiation to space. We will use satellite data from the Tropical Rainfall Measuring Mission and International Satellite Cloud Climatology Project to illustrate how rainfall and convective cloud properties respond to changes in convective strength, temperature and large-scale dynamics in the current climate. The observations, combined with GCM predictions of thermodynamic structure changes, suggest that warmer climates might be characterized by greater rainfall rates, more extensive anvil cloud cover and higher top altitudes, while albedos and ice water paths remain fairly constant. The observations provide constraints on the convective water budget that are useful in evaluating diagnostic and prognostic parameterizations of cumulus updraft speeds and cumulus detrainment.