Single-column model simulations of arctic cloudiness and surface radiative fluxes during the Surface Heat Budget of the Arctic (SHEBA) experiment

Clouds play a fundamental role in the climate system through their impacts on the radiative, moisture, and heat budgets. Hence, a high priority in climate modeling is to have an accurate representation of important cloud processes. This is especially true over the Arctic Ocean because the magnitude of the surface temperature amplification is dependent upon the ice-albedo feedback, which in turn is sensitive to cloud processes. However, typical General Circulation Models (GCMs) fail to predict realistic cloud amounts over the Arctic Ocean and this is a critical issue for producing accurate predictions of Artic climate changes. Single-column models (SCMs) with prescribed large-scale forcing are commonly used for testing parameterizations developed for GCMs. For the Arctic, the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment provides a comprehensive observational dataset that allows initializing, forcing and evaluating SCM simulations of the Arctic during all phases of the annual cycle. Simulations are conducted both with the SCM version 3.6 of the NCAR Community Climate Model (CCM) and with a Stratocumulus 1D model that includes prognostic equations for cloud water and ice content. The models are initialized and forced with a dataset derived from the reanalysis of the ECMWF (European Centre for Medium-Range Weather Forecasts) for the SHEBA experiment. Other SHEBA datasets including lidar, radar and meteorological surface observations are used to evaluate the simulations. Typical winter and summer regimes have been integrated with the NCAR SCM. During winter, this model predicts too-cloudy skies associated with colder than observed temperatures and unrelaistically high humidity profiles. In constrast, the model underestimates summertime cloud amount and relative humidity and overestimates the temperatures. As the ice cloud amount is more important during winter, this may suggest that ice-phase processes are essential in determining the low-cloud amount over the Arctic. Additionally, experiments using a Stratocumulus 1D model that includes prognostic equations for cloud water and ice content will be discussed.