A235-05
The Spatiotemporal Variability of Cloud Radiative Effects on the Greenland Ice Sheet Surface Mass Balance

Wednesday, 16 December 2020: 07:13
Virtual
Maaike Izeboud, Delft University of Technology, Delft, Netherlands, Stef Lhermitte, Delft University of Technology, Geoscience and Remote Sensing, Delft, Netherlands, Jan Lenaerts, University of Colorado Boulder, Department of Atmospheric and Oceanic Sciences, Boulder, CO, United States, Kristof Van Tricht, VITO, Remote Sensing, Mol, Belgium, Nander Wever, University of Colorado Boulder, Department of Atmospheric and Oceanic Sciences, Boulder, United States and Nicole P.M. Van Lipzig, KULeuven, Leuven, Belgium
Abstract:
To better understand and quantify the impact of clouds on the Greenland Ice Sheet surface mass balance (SMB), we study the spatiotemporal variability of the cloud radiative effect (CRE). We perform multiple simulations with the SNOWPACK model for 2001-2010 with meteorological data that is obtained from the regional climate model RACMO2.3p2. We also separate the total CRE into short‐term and long‐term impacts. The short-term quantifies the effect of each, individual cloudy day on the SMB compared to clear-sky conditions on that day, while the long-term assess the effect of pre-conditioning the snow.

Our results show that overall clouds warm the GrIS (16.8 ± 4.5 W/m2) for all seasons, except in summer over the ablation area where they cool (−6.4 ± 5.7 W/m2). The cloud radiative warming effects yield a reduction of the SMB (-157 Gt/yr) caused primarily by reduced melt-water refreezing and enhanced sublimation rates. The impact of cloud radiative cooling effects is an enhanced SMB (121 Gt/yr) mainly through the blocking of SW radiation and stabilisation of the albedo-melt feedback. The cloud-enhanced SMB effect in the ablation area is stronger per square meter than the cloud-reduced SMB effect in the accumulation area, but negative SMB effects occur over a longer period and ten-fold area. Hence outweighing the cloud-enhanced SMB and resulting in a relative mass loss of -36 Gt/yr due to clouds.

Furthermore, our results show competing short-term and long-term effects over the ablation area. Short-term cooling effects occur through SW radiation blocking. Long-term warming effects are a result of the pre-conditioning of the snow: a decrease in albedo increases SW absorption. This long-term effect can further enhance (summer) melt.

Our results demonstrate the complex role of cloud radiation on GrIS SMB. The impact of the CRE, determined by spatial, temporal and initial conditions, explains existing conflicted views on the role of cloud radiation and emphasises the need for accurate cloud and albedo representations in future studies.

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