How well do the regional atmospheric, oceanic and coupled models describe the Antarctic sea ice albedo?

A realistic representation of the Antarctic sea ice surface albedo, especially during the melting period, is essential to obtain reliable atmospheric and oceanic model predictions. Antarctic sea ice cover influences the atmosphere by reflecting solar radiation and acting as a barrier between the atmosphere and the ocean, for example. The Antarctic sea ice consists of ice floes of varying thickness, usually covered by snow, and broken up by cracks, leads and polynyas. Therefore, the optical properties of sea ice can vary greatly.

We use regional atmospheric (HCLIM-AROME), oceanic (MetROMS-UHel) and coupled (MAR-NEMO) models to compare the representation of the basic sea ice characteristics: sea ice albedo, snow and ice thickness, and meteorological data during the melt periods of two Antarctic domains with very different sea ice conditions, using data of the ISPOL and Marsden field campaigns. During the ISPOL campaign (Dec 2004; Hellmer et al. 2008) RV Polarstern was moored to an ice floe in the Weddell Sea, where snow-covered multi-year ice persists. The Marsden field campaign (Nov. 2022; Dadic et al. 2023) was established over 2.4m thick land-fast ice of McMurdo Sound, where snow thickness ranged from 0 to 40 cm in patches over the roughest ice. We aim to bridge the models to observations, by comparing model output to various levels of observations, from in-situ measurements of the ISPOL and Marsden campaigns to smaller/larger scale satellite observations over Weddell and Ross Seas. 

The first comparisons revealed that HCLIM, with a simplistic 1D thermodynamic sea ice scheme (SICE, Bartrak et al. 2018), was underestimating snow albedo up to 30%, and needed retuning for Antarctic conditions. Overall, preliminary results indicate that the models do well reproducing the snow-covered sea ice during the ISPOL campaign, when the weather was warm, with the air temperature mostly above −5◦C. MetROMS-UHel, which uses the Delta-Eddington multiple scattering radiative transfer model to calculate the sea ice albedo, even reproduced similar diurnal variability than observed. The Marsden field campaign took place in an area of complex topography, cold weather conditions, and greatly varying sea ice. The models tend to overestimate the albedo of the land-fast ice of the Marsden field campaign, as a uniform, instead of patchy, snow layer is modelled. Models also cannot reproduce the variety of sea ice, such as freshly formed ice, in the McMurdo Sound area apparent on the satellite images.