Implementation of Accurate, Interactive Sea Ice Radiative Transfer into the GISS GCM and Its Impact on the Solar Radiation Distribution in the Arctic Atmosphere-Sea Ice-Ocean System

A multiple-stream radiative transfer scheme for sea ice suitable for GCM applications is introduced. The algorithm explicitly considers the refraction at the air-ice and air-water interfaces and the multiple scattering by inclusions entrapped in the ice, such as brine pockets and air bubbles. The integrated brine and air volumes are derived from the ice physical properties (salinity, density and temperature) based on phase equilibrium relationships. Thus, the AOPs are linked to the sea ice IOPs through the ice physical properties, which are used as the input variables for the radiative transfer computations. This physically based approach provides a sophisticated and complete treatment for the radiation transport in sea ice, and facilitates its inclusion in climate models. The new radiative transfer scheme is implemented into the GISS climate model to calculate the sea ice albedo, solar radiation transmission and internal ice absorption. These radiative variables are fed back to the sea ice thermodynamic module to simulate the ice properties, so that radiation, ice properties and thermodynamics are interactively coupled. Model experiments show that the new sea ice radiation physics significantly influence the solar radiation distribution in the atmosphere-sea ice-ocean system, especially the shortwave attenuation in the ice and the transmission into the ocean beneath. The melting at the ice top is highly correlated with the net shortwave radiation at the surface, whereas the basal melting is highly correlated with the shortwave transmission. The modeled albedo is generally consistent with surface- and satellite-based observations.