Abstract
Abstract. Radiative transfer in snow and ice is often not modeled explicitly in regional climate models. In this study, we evaluate a new englacial radiative transfer scheme and assess the surface mass and energy budget for the Greenland ice sheet in the latest version of the regional climate model RACMO2, version 2.3p3. We also evaluate the modeled (sub)surface temperature and melt, as radiation penetration now enables internal heating. The results are compared to the previous model version and are evaluated against stake measurements and automatic weather station data of the K-transect and PROMICE projects. In addition, subsurface snow temperature profiles are compared at the K-transect, Summit, and southeast Greenland. The surface mass balance is in good agreement with observations, with a mean bias of −31 mm w.e. yr−1 (−2.67 %), and only changes considerably with respect to the previous RACMO2 version around the ice margins and near the percolation zone. Melt and refreezing, on the other hand, are changed more substantially in various regions due to the changed albedo representation, subsurface energy absorption, and meltwater percolation. Internal heating leads to higher snow temperatures in summer, in agreement with observations, and introduces a shallow layer of subsurface melt. Hence, this study shows the consequences and necessity of radiative transfer in snow and ice for regional climate modeling of the Greenland ice sheet.
Highlights
The Greenland ice sheet (GrIS) has been losing mass at an accelerating pace in the last decade (Box and Colgan, 2013; Kjeldsen et al, 2015; Bevis et al, 2019; Shepherd et al, 2020)
Snow and ice melt leading to extensive runoff typically dominates the surface mass balance (SMB) around the margins of the GrIS, leading to mass loss of up to 3 m water equivalent (w.e.) yr−1, while snowfall dominates in the interior (Van den Broeke et al, 2016)
The plane-parallel broadband snow albedo scheme based on Gardner and Sharp (2010) is replaced by the Two-streAm Radiative TransfEr in Snow Model (TARTES; Libois et al, 2013), which is coupled to RACMO2 with the Spectralto-NarrOWBand ALbedo (SNOWBAL) module version 1.2 (Van Dalum et al, 2019)
Summary
The Greenland ice sheet (GrIS) has been losing mass at an accelerating pace in the last decade (Box and Colgan, 2013; Kjeldsen et al, 2015; Bevis et al, 2019; Shepherd et al, 2020). C. T. van Dalum et al.: RACMO2.3p3 GrIS SMB and energy budget spatial coverage and temporal sampling to fully capture these events, while satellites cannot adequately quantify melt rates, and the use of climate models is required (Rae et al, 2012; Goelzer et al, 2013; Leeson et al, 2018; Alexander et al, 2019). A considerable part of incoming shortwave radiation, penetrates through the surface, heating snow and ice layers below (Kuipers Munneke et al, 2009; Warren, 2019; He and Flanner, 2020). The new version RACMO2.3p3, Rp3, incorporates a new snow and ice albedo and radiative transfer scheme, which includes internal heating by radiation penetration, and updates to the firn module (Van Dalum et al, 2020a).
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