Physics of snow cover in the climate model INMCM

Snow cover has a great influence on the energy balance on the surface, in particular ability to reflect solar radiation. As well as radiation, when modeling the climate, it is important to correctly describe the water cycle. During the transitional seasons, when the temperature fluctuates around zero degrees Celsius, some of the melt water can be retained in the snow layer and refreeze. In addition, over time after a snowfall the snow becomes denser. Aged, wet, refrozen snows have different optical properties than new-fallen snow, in particular a lower albedo. Moreover, atmospheric aerosols falling on a snow-covered surface leads to its pollution and, as a consequence, reduces its reflectivity. Aerosols such as mineral dust and black carbon have the greatest effect on the albedo and radiation balance.

In the climatу model INMCM, some physical features of snow cover have been implemented. The porous structure of the snow is taken into account and the calculation of the water content of the snow layer is realized. During snowmelt, the ratio of the water is retained in the pores, and does not go immediately to the upper boundary of the soil. The possibility of refreezing of melt water contained in the snow layer has also been implemented. The change in snow density over time is taken into account. At the same time, it is assumed that the snow layer consists of a mixture of usual and refrozen snow, as well as melt water contained in snow pores. The influence of the composition of the snow layer and its density on the reflectivity is taken into account. The effect on the albedo of impurities contained in snow is also taken into account (for example, black carbon). Computational experiments were carried out with the INMCM model to assess the sensitivity to the realized physical processes.

This work is supported by the Russian Science Foundation, project No. 20-17-00190.