Regional grid refinement in an Earth system model: impacts on the simulated Greenland surface mass balance

Leonardus Van Kampenhout,Jan T M Lenaerts,Adam R Herrington,William J Sacks,Alan M Rhoades,Colin M Zarzycki,Michiel R Van Den Broeke

doi:10.5194/tc-13-1547-2019

Abstract

Abstract. In this study, the resolution dependence of the simulated Greenland ice sheet surface mass balance (GrIS SMB) in the variable-resolution Community Earth System Model (VR-CESM) is investigated. Coupled atmosphere–land simulations are performed on two regionally refined grids over Greenland at 0.5∘ (∼55 km) and 0.25∘ (∼28 km), maintaining a quasi-uniform resolution of 1∘ (∼111 km) over the rest of the globe. On the refined grids, the SMB in the accumulation zone is significantly improved compared to airborne radar and in situ observations, with a general wetting (more snowfall) at the margins and a drying (less snowfall) in the interior GrIS. Total GrIS precipitation decreases with resolution, which is in line with best-available regional climate model results. In the ablation zone, CESM starts developing a positive SMB bias with increased resolution in some basins, notably in the east and the north. The mismatch in ablation is linked to changes in cloud cover in VR-CESM, and a reduced effectiveness of the elevation classes subgrid parametrization in CESM. Overall, our pilot study introduces VR-CESM as a new tool in the cryospheric sciences, which could be used to dynamically downscale SMB in scenario simulations and to force dynamical ice sheet models through the CESM coupling framework.

Highlights

The contribution of the Greenland ice sheet (GrIS) to global sea level rise is increasingly determined through its surface mass balance (SMB) (van den Broeke et al, 2016)
We argue that it is fair to compare variable-resolution Community Earth System Model (VR-Community Earth System Model (CESM)) directly to the downscaled 1 km RACMO2 product as (i) CESM performs online downscaling using the semi-statistical elevation classes (Sect. 2.3), and (ii) best-estimate data are preferred in order to identify either model improvements or regressions, in line with the purpose of this paper
It is surrounded by a band of negative height anomalies in all three simulations, with one of the minima approximately centred over Iceland–south Greenland, indicating more cyclonic flow over the GrIS in CESM

Summary

Introduction

The contribution of the Greenland ice sheet (GrIS) to global sea level rise is increasingly determined through its surface mass balance (SMB) (van den Broeke et al, 2016). Accurate estimates of future GrIS SMB are key in providing projections for sea level rise. The most realistic SMB projections to date are derived from general circulation model (GCM) scenario output downscaled using regional climate models RCMs typically run at a horizontal grid resolution of O(10 km) whereas atmospheric GCMs are typically run using 1◦ or O(100 km) grids. A fine spatial resolution seems indispensable for resolving narrow ablation zones found around the GrIS margins (Lefebre et al, 2005; Pollard, 2010)

Methods

Results

Conclusion