Albedo, snowpack

The physical impact of the snowpack depends on its physical properties, such as albedo and heat conductivity. Its chemical impact depends on its chemical composition and its reactivity, determined in part by the light flux inside the snowpack. All of these properties change with time, because of a set of physical and chemical processes regrouped under the term snow metamorphism , defined below. 

Snow is a porous medium formed of air, ice crystals and small amounts of chemical impurities. Because ice has a high vapor pressure (165 Pa at -15°C, 610 Pa at 0°C), the vertical temperature gradient that is almost always present within the snowpack generates sublimation and condensation of water vapor that change the size and shape of snow crystals. This results in changes in physical variables such as density, albedo, heat conductivity, permeability and hardness. These physical changes have formed the basis for the definition of snow metamorphism. ... 

Next to the temperature gradient inside the snowpack, an important driving force for snow metamorphism is wind, that lifts, transports and redeposits snow crystals, changing snowpack mass and density " and deposits aerosols inside the snowpack.Wind and temperature are climatic variables that determine metamorphism and snowpack physical properties such as albedo and heat conductivity. These properties affect the energy balance of the snow-atmosphere and of the soil-snow interfaces, which in turn affect climate. 

Variables such as density, albedo, light e-folding depth, specific surface area (SSA), crystal size and shape, heat conductivity, permeability, diffusivity and shear resistance are required for a complete physical description of the snowpack. Not all these variables have major relevance to climatic issues. Albedo, i.e. the fraction of incident light that is reflected, has obvious climatic relevance and is discussed here. It depends in part on crystal size and shape and this dependence can in fact more simply be related in part to the SSA of the snow i.e. the surface area accessible to gases per unit mass. ... 

Since both albedo and gas adsorption depend on SSA, the climate response of the concentration of species adsorbed within the snowpack will be similar to that of albedo increase in regions where warming is accompanied by a change from HGM to QIM, such as the southern taiga and the warmer Alpine areas in the fall and decrease in the other regions. These effects will be modulated by the temperature increase, that will decrease the concentration of adsorbed species. For example, a temperature rise from -15 to -10 °C will desorb 40% of adsorbed acetone molecules, that have an adsorption enthalpy of 57 kJ/mol,, at constant SSA. The combined effect of warming and SSA change will then probably lead to a decrease in the concentration of adsorbed species in most areas. 

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