In the Jutulgryta area of Dronning Maud Land, Antarctica, subsurface melting of
the ice sheet has been observed. The melting takes place during the summer
months in blue-ice areas under conditions of below-freezing air and surface
temperatures. Adjacent snow-covered regions, having the same meteorological and
climatic conditions, experience little or no subsurface melting. To help explain
and understand the observed melt-rate differences in the blue-ice and
snow-covered areas, a physically based numerical model of the coupled
atmosphere, radiation, snow and blue-ice system has been developed. The model
comprises a heat-transfer equation which includes a spectrally dependent
solar-radiation source term. The penetration of radiation into the snow and blue
ice depends on the solar-radiation spectrum, the surface albedo and the snow and
blue-ice grain-sizes and densities. In addition, the model uses a complete
surface energy balance to define the surface boundary conditions. It is run over
the full annual cycle, simulating temperature profiles and melting and freezing
quantities throughout the summer and winter seasons. The model is driven and
validated using field observations collected during the Norwegian Antarctic
Research Expedition (NARE) 1996–97. The simulations suggest that the
observed differences between subsurface snow and blue-ice melting can be
explained largely by radiative and heat-transfer interactions resulting from
differences in albedo, grain-size and density between the two mediums.