Simulating the Greenland atmospheric boundary layer Part II: Energy balance and climate sensitivity

Abstract

A three-dimensional dynamic downscaling model of the Greenland atmospheric boundary layer is usedto investigate the surface energy balance of the Greenland ice sheet for the summer ablation season of1998. The model is forced by ECMWF analysis data and has a horizontal resolution of 20 km. Theresults show that the turbulent heat fluxes contribute significantly (32%) to the total surface energy fluxin the ablation region. A climate sensitivity experiment is carried out with the model by increasing thefree atmospheric forcing temperature by 1 K. The resulting change, known as climate sensitivity, in2 m temperature, 2 m wind speed and the surface energy balance components are discussed. The 2 mtemperature is shown to have a climate sensitivity significantly less than unity, as low as 0.3, in regionswhere melt prevails for most of the ablation season. The surface energy flux in the ablation region isfound to increase by 21% for a 1 K increase in atmospheric temperature. Wind speeds also increase, particularly near the margin of the ice sheet, as a result of enhanced katabatic forcing. Enhanced windspeeds are shown to account for roughly 12% of the climate sensitivity of the sensible heat flux whenaveraged over the ablation region. Albedo feedback is also shown to play an important role in the totalclimate sensitivity of the surface energy balance.