28 August 2013

Simulating Greenland's Surface Mass Balance in the Community Earth System Model

Science

The surface mass balance (SMB) of a glacier or ice sheet is defined as the difference between accumulation (mainly snowfall) and ablation (mainly surface melting and runoff). The average SMB for the Greenland ice sheet is positive in the cold interior, where there is little or no summer melting, and negative along the warmer margins where summer melting can exceed winter snowfall. Greenland’s SMB has previously been simulated by high-resolution regional models such as RACMO2, which has been extensively validated against observations. Until now, however, global climate models have not been considered suitable for simulating ice sheet SMB because of model biases and insufficient resolution.

Approach

Climate scientists in the Netherlands (Utrecht University) and the U.S. (Los Alamos National Laboratory and the National Center for Atmospheric Research) have evaluated a new surface-mass-balance (SMB) scheme for ice sheets in the Community Earth System Model (CESM). This study analyzes the Greenland SMB simulated for 1850-2005 by CESM, in which the SMB is computed in the land model for multiple elevation classes on a 1o grid and then is downscaled to the finer 5-km ice sheet grid. Through comparison to observations and RACMO2 output, it is shown that CESM can simulate a realistic SMB for the Greenland ice sheet. The simulated mean SMB for 1960-2005 is 359 ± 120 Gt/yr, in the range of estimates from regional models. CESM correctly simulates the major ablation areas. It is able to simulate the bands of precipitation maxima along the southeast and northwest margins, but precipitation rates are underestimated along the southeast margin and overestimated in the high interior. Future work will focus on reducing the remaining biases.

Impact

CESM is the first global climate model that can simulate a realistic surface mass balance for the Greenland ice sheet. This success is attributed to a lack of major climate biases, a sophisticated snowpack model, and the use of elevation classes for downscaling.

Contact
Siyu Chen
Funding
Acknowledgments

This work was supported by the Earth System Modeling program of the Office of Biological and Environmental Research within the US Department of Energy’s Office of Science.