Improved sea ice shortwave radiation physics in CCSM4: The impact of melt ponds and aerosols on Arctic Sea ice

For sea ice, the most notable improvements are the incorporation of a new shortwave radiative transfer scheme and the capabilities that this enables. This scheme uses inherent optical properties to define scattering and absorption characteristics of snow, ice, and included shortwave absorbers and explicitly allows for melt ponds and aerosols.

The deposition and cycling of aerosols in sea ice is now included, and a new parameterization derives ponded water from the surface meltwater flux. Taken together, this provides a more sophisticated, accurate, and complete treatment of sea ice radiative transfer. In preindustrial CO₂ simulations, the radiative impact of ponds and aerosols on Arctic sea ice is 1.1 W m⁻² annually, with aerosols accounting for up to 8 W m⁻² of enhanced June shortwave absorption in the Barents and Kara Seas and with ponds accounting for over 10 W m⁻² in shelf regions in July.