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

A three-dimensional dynamic downscaling model of the Greenland atmospheric boundary layer is used to investigate the surface energy balance of the Greenland ice sheet for the summer ablation season of 1998. The model is forced by ECMWF analysis data and has a horizontal resolution of 20 km. The results show that the turbulent heat fluxes contribute significantly (32%) to the total surface energy flux in the ablation region. A climate sensitivity experiment is carried out with the model by increasing the free atmospheric forcing temperature by 1 K. The resulting change, known as climate sensitivity, in 2 m temperature, 2 m wind speed and the surface energy balance components are discussed. The 2 m temperature is shown to have a climate sensitivity significantly less than unity, as low as 0.3, in regions where melt prevails for most of the ablation season. The surface energy flux in the ablation region is found 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 when averaged over the ablation region. Albedo feedback is also shown to play an important role in the total climate sensitivity of the surface energy balance.