Recent improvements of the melt pond albedo parametrization in HIRHAM-NAOSIM

The spread of climate model results in terms of quantifying the sea ice surface albedo feedback is partly caused by the sensitivity of the simulated sea ice surface albedo to surface warming. The accurate representation of the Arctic sea ice and its evolution throughout the year, particularly in the melting period, is crucial to obtain reliable climate model projections.

The rapidly warming Arctic leads to changes in sea ice properties. Arctic sea ice is becoming younger, transitioning from rough multi-year ice to flatter first-year ice. This influences the distribution and occurrence of melt ponds, which increase surface heterogeneity during the melting season. As a result, the surface albedo is altered and modelling it becomes more complex. However, many models are not able to simulate ice properties, like surface roughness, which would be beneficial for simulating melt pond fractions. A new melt pond fraction parametrization for the coupled Arctic climate model HIRHAM-NAOSIM has been developed using satellite data. This new parametrization includes a retarded response to temperature changes with different change rates for thin and thick ice. By taking only surface temperature and ice thickness as input variables, this parametrization can be applied to many climate models. An offline analysis with satellite data shows a higher correlation between the new parametrization and satellite observations (R=0.71) compared to the old parametrization (R=0.62). The offline analysis, first model results, and a comparison of model results with MOSAIC and satellite observations will be presented. The effects of the new parametrization on the radiative energy balance will be discussed.