Model Evaluation in Central Greenland Using a Comprehensive Set of Atmospheric and Surface Measurements

In order to reconstruct and forecast the mass balance of the Greenland Ice Sheet we must understand the processes that occur at the atmosphere/ice interface. Surface temperature is the linchpin that connects the subsurface to the atmospheric boundary-layer and is changed by a surplus or deficit of the surface energy budget (SEB). The SEB is a balance of radiative, sensible, latent and ground heat flux. As the temperature approaches the melting point of snow the surface energy budget is important in determining if melt will occur. Once the threshold is reached the SEB determines how much water will be converted to liquid, affecting the global sea level and fresh water input into regional oceans.

At Summit Station, in central Greenland, liquid-bearing clouds increase the downwelling radiation compared to clear-sky scenes and scenes containing predominately ice-clouds.  Cloud radiative forcing, due to all cloud types, increases the net radiation at the surface throughout the year due to a relatively constant surface albedo.  Yet an increase or decrease in forcing terms (downwelling longwave and net shortwave radiation) is compensated by a response of the other SEB terms (upwelling longwave radiation, sensible, latent, and ground heat flux). The upwelling longwave radiation, which is proportional to the surface temperature to the fourth power, responds by 55-75% in summer compared to 40-50% in winter. In summer the latent heat flux response increases, the ground heat flux response decreases, and the sensible heat flux response remains relatively constant.

Using these detailed observations we evaluate the ability of ERA-Interim, NOAA-NCEP, and the Community Earth System Model to accurately represent cloud presence and phase. Next we determine if cloud radiative forcing elicits a physically realistic response in the latent, sensible and ground heat fluxes.  Ultimately these results are used to evaluate biases in surface temperatures on seasonal and diurnal time scales.   Process-based model evaluation of this nature provides the understanding necessary to pinpoint reasons for surface temperature discrepancies, ensuring that future climate projections and current reanalysis data, which are often us as “truth”, are representative of the physical processes occurring in central Greenland.