Sensitivity of Greenland Ice Sheet surface mass balance to surface albedo parameterization: a study with a regional climate model

Abstract

Abstract. We present a sensitivity study of the surface mass balance (SMB) of the Greenland Ice Sheet, as modeled using a regional atmospheric climate model, to various parameter settings in the albedo scheme. The snow albedo scheme uses grain size as a prognostic variable and further depends on cloud cover, solar zenith angle and black carbon concentration. For the control experiment the overestimation of absorbed shortwave radiation (+6 %) at the K-transect (west Greenland) for the period 2004-2009 is considerably reduced compared to the previous density-dependent albedo scheme (+22 %). To simulate realistic snow albedo values, a small concentration of black carbon is needed, which has strongest impact on melt in the accumulation area. A background ice albedo field derived from MODIS imagery improves the agreement between the modeled and observed SMB gradient along the K-transect. The effect of enhanced meltwater retention and refreezing is a decrease of the albedo due to an increase in snow grain size. As a secondary effect of refreezing the snowpack is heated, enhancing melt and further lowering the albedo. Especially in a warmer climate this process is important, since it reduces the refreezing potential of the firn layer that covers the Greenland Ice Sheet.

Evaluation of the updated regional climate model RACMO2.3: summer snowfall impact on the Greenland Ice Sheet

“…5d). In contrast, simulated summer snowfall has not considerably changed at station S9 for the period -2012) and biases in albedo and melt energy have persisted ( Fig. 5d and f).…”

“…Among other changes, the rainfall-to-snowfall conversion has been revised and an ice supersaturation parameterization included to favour solid over liquid precipitation in summer and reduce the overestimated coastal cloud cover and precipitation simulated in pre- vious versions, respectively (Van de Berg et al, 2006). The subsequent increase in modelled summer snowfall has generally improved the representation of surface energy balance (SEB) and surface mass balance (SMB) along the K-transect in west Greenland.…”

“…1, white dots). Since 1990, annual stake measurements have been performed at eight sites along the transect: S4, S5, SHR, S6, S7, S8, S9 and S10 ( Van de Wal et al, 2005, 2012. Since August 2003, three AWS with the capability to close the SEB have been operated at sites S5 (∼ 500 m a.s.l.…”

Albedo over rough snow and ice surfaces

“…The magnitude of these reductions depends primarily on the penitente opening angle, but also the shape and spatial variability of the material albedo play a major role. Including surface roughness in the current parameterizations of surface albedo (e.g., Gardner and Sharp, 2010;van Angelen et al, 2012) is therefore essential if we want to correctly represent albedo in energy balance models over complex, rough terrain. Up to now, the representation of penitentes in energy balance models has typically been done based on albedo measurements derived from shortwave radiation sensors or remote sensing data (e.g., Corripio and Purves, 2005;Pellicciotti et al, 2008;Winkler et al, 2009).…”

“…Moreover, it is important to include surface roughness in the current parameterizations of surface albedo (e.g., Gardner and Sharp, 2010;Kuipers Munneke et al, 2011;van Angelen et al, 2012), certainly when they are used over surfaces with prominent macroscopic surface roughness. This is because over these surfaces the assumption that albedo reductions due to surface roughness occur only at high solar zenith angles, which have little impact on the overall surface energy balance (Gardner and Sharp, 2010;Warren et al, 1998), is no longer true.…”