Abstract
Abstract. Changing climate conditions on Greenland influence the snow accumulation rate and surface mass balance (SMB) on the ice sheet and, ultimately, its shape. This can in turn affect local climate via orography and albedo variations and, potentially, remote areas via changes in ocean circulation triggered by melt water or calving from the ice sheet. Examining these interactions in the IPSL global model requires improving the representation of snow at the ice sheet surface. In this paper, we present a new snow scheme implemented in LMDZ, the atmospheric component of the IPSL coupled model. We analyse surface climate and SMB on the Greenland ice sheet under insolation and oceanic boundary conditions for modern, but also for two different past climates, the last glacial inception (115 kyr BP) and the Eemian (126 kyr BP). While being limited by the low resolution of the general circulation model (GCM), present-day SMB is on the same order of magnitude as recent regional model findings. It is affected by a moist bias of the GCM in Western Greenland and a dry bias in the north-east. Under Eemian conditions, the SMB decreases largely, and melting affects areas in which the ice sheet surface is today at high altitude, including recent ice core drilling sites as NEEM. In contrast, glacial inception conditions lead to a higher mass balance overall due to the reduced melting in the colder summer climate. Compared to the widely applied positive degree-day (PDD) parameterization of SMB, our direct modelling results suggest a weaker sensitivity of SMB to changing climatic forcing. For the Eemian climate, our model simulations using interannually varying monthly mean forcings for the ocean surface temperature and sea ice cover lead to significantly higher SMB in southern Greenland compared to simulations forced with climatological monthly means.
Highlights
Among the conditions determining the long-term evolution of an ice sheet, the amount of snow and ice accumulated on its surface is of primary importance
Van de Berg et al (2011) use a regional model nested into a general circulation model (GCM) and show that the change of melt for the Eemian calculated by a positive degree-day (PDD) method appears to be 30 % lower than the one in their model, questioning the validity of the PDD approach for past climate, as concluded by Ganopolski and Robinson (2011)
After describing the model versions used and the simulations performed in Sect. 2, we evaluate the effect of using an improved versus a simplistic snow scheme in the LMDZ GCM (Sect. 3.1) and compare the surface mass balance (SMB) obtained by the model to the SMB estimated with a PDD method (Sect. 3.2) for modern and paleo climates, respectively
Summary
Among the conditions determining the long-term evolution of an ice sheet, the amount of snow and ice accumulated on its surface is of primary importance. Van de Berg et al (2011) use a regional model nested into a GCM and show that the change of melt for the Eemian calculated by a PDD method appears to be 30 % lower than the one in their model, questioning the validity of the PDD approach for past climate, as concluded by Ganopolski and Robinson (2011) We complement these studies with the following approach: a comprehensive snow scheme already in use for regional studies (Gallee et al, 2001; Fettweis, 2007; Fettweis et al, 2011) is integrated into the global atmospheric circulation model LMDZ.
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