Analysis of clear-sky Antarctic snow albedo using observations and radiative transfer modeling

A radiative transfer model for studying spectral and broadband snow surface albedo has been applied to radiation data (1998-2001) from different climate regimes in Antarctica. The model makes use of the doubling-adding method for radiative transfer, combined with the correlated k-distribution technique to account for atmospheric gas absorption. Snow layers are described by scattering phase functions for irregular hexagonal plate-shaped ice crystals. Multiple scattering is included, as well as the option to include soot in the snowpack, as well as clouds. Sensitivity experiments show that the model is capable of calculating spectral and broadband albedos as a function of solar zenith angle and effective snow grain radius re. The novel approach of applying the model to multiple-year field data of clear-sky albedo from five locations in Dronning Maud Land, Antarctica, reveals that seasonal clear-sky albedo variations (0.77-0.88) are dominantly caused by strong spatial and temporal variations in re. Summer season averages of re range from 22 mm on the Antarctic plateau to 64 mm on the ice shelf. Maximum monthly values of re are 40-150% higher. Other factors influencing clear-sky broadband albedo are the seasonal cycle in solar zenith angle (at most 0.02 difference in summer and spring/autumn albedo) and the spatial variation in optical thickness of the cloudless atmosphere (0.01 difference between ice shelves and plateau). The seasonal cycle in optical thickness of the atmosphere was found to be of minor importance (< 0.005 between summer and spring/autumn).