Seasonal evolution of snow density and its impact on thermal regime of sea ice during the MOSAiC expedition

Abstract. Snow density is a crucial parameter for snow and sea ice modelling at the physical process level. The seasonal evolution of surface (top 3 cm) and bulk (entire layer) snow densities observed during MOSAiC expedition were investigated and used to access several snow density schemes. A numerical snow and sea ice model was applied to simulate the impact of snow density on the thermal regime of sea ice during the period when snow was dry. The constant snow densities of 348 kg/m³, 308 kg/m³ and 487 kg/m³ were derived from linear regression of snow water equivalent (SWE) versus snow depth, using samples collected during the entire MOSAiC period, the winter-spring period (October–May), and summer-autumn period (June–September), respectively. The examined snow density schemes produced mean snow densities consistent with MOSAiC observations; however, none of the schemes adequately captured the observed temporal variability. The modelled mean surface temperature and ice thickness were linearly related to the snow density, whereas the modelled mean in-snow and in-ice temperatures had linear inverse relationships with the snow density. The impacts of time-dependent snow density on snow and ice thermodynamic regimes were stronger than in the model runs using constant snow density. Model sensitivity experiments revealed contrasting responses of the snow and ice system to changes in snow density and precipitation. Increased snow density decreased snow and ice temperatures, promoting ice growth, while increased precipitation led to warmer snow and ice temperatures and reduced ice thickness.