SIMULATION AND VALIDATION OF ARCTIC RADIATION AND CLOUDS IN A REGIONAL CLIMATE MODEL

A regional atmospheric climate model has been applied to simulate the Arctic climate north of 65 degrees N at a 50 km horizontal resolution for January and July 1990. The monthly mean components of the surface radiative balance and clouds using ECHAM3 parameterization have been d escribed and compared with data. The model overestimates the incoming shortwave flux, over-estimates clouds during January, and underestimat es clouds during July. The high-resolution simulations show many regio nal details due to regionally different surface temperatures, clouds, surface albedo, and snow depths. The bias in the model simulation can be reduced by using the ECHAM4 parameterization. The use of the ECHAM4 radiation parameterization clearly improves the results, due to the b etter description of atmospheric absorption. Sensitivity experiments w ith different cloud parameters (drop size, droplet concentration, clou d phase) have been described. The simulated changes due to these cloud parameter changes occur in a very small spatial scale and are of simi lar order as the model bias itself.