Understanding cloud formation mechanisms and cloud feedbacks

Changes in cloud amount, vertical distribution, and microphysical characteristics are expected to accompany global warming and further modify climate, but the magnitude and sign of this feedback remain uncertain. Recent studies have shown significant trends in Arctic cloud amount over the last two decades, accompanied by an overall increase in surface temperature. A trend in Arctic cloud amount may be the result of local processes such as enhanced evaporation, or it may result from changes in large-scale circulation and heat and moisture transport into the Arctic. What is the relative role of these processes in Arctic climate change? Satellite data has been used to monitor the Arctic since the late 1970s and thus provides the opportunity to examine clouds formation mechanisms and cloud feedbacks over time. Products from the extended AVHRR Polar Pathfinder (APP-x) data set, including cloud amount, cloud microphysical characteristics, surface air-temperature, and cloud radiative effects, are combined with heat and moisture fluxes from the TOVS Path-P data set over the period 1982-2000 for this analysis. Additionally, detailed measurements of cloud amount and microphysical characteristics, surface temperature, surface heat and moisture flux, and horizontal heat and moisture advection collected during Surface Heat Budget of the Arctic Ocean (SHEBA) field campaign are employed. Preliminary results show that anomalies of high cloud amount vary with moisture flux anomalies over the Arctic (70°N north to the pole) from 1992 through 1998, and that total cloud cover anomalies vary with snow/ice cover anomalies from 1992 through 1998, but are out of phase.