Snow structure and depth hoar formation in Mizuho Plateau, Antarctica

The development of depth hoar was investigated for four 30-m snow cores in Mizuho Plateau, Antarctica, with measurements of specific area of internal free surfaces and air permeability. Both the specific area and air permeability increased with increasing porosity for the four cores. But the specific area at a given porosity was smaller for the core in a region having a smaller accumulation rate. The air permeability at a given porosity was larger in a region having a smaller accumulation rate. Degrees of orientation were extremely large in a region having a smaller accumulation rate, showing the development of vertical structure. It was concluded that the development of depth hoar was larger at a smaller accumulation rate. The dominant factor of the development of depth hoar was discussed with reference to the variations of snow temperature at the four stations of core sampling. The development of depth hoar is essentially determined not only by the temperature gradient in snow but also by the staying period near the surface where the temperature gradient is largest. Thus the accumulation rate is an important factor in determining the characteristic structure of snow in polar regions. A physical quantity, cumulative thermogradient, is introduced to describe the degree of depth hoar development at a given site