© International Glaciological Society AIR AND WATER-VAPOUR CONVECTION IN SNOW by

Heat and mass transport by an air and water-vapour mixture (pore air) in snow due to thermal convection has been computed. It can be shown theoretically that thermal convection is always occuring in newly fallen snow, but never occurs in snow with rounded grains. Rayleigh numbers of depth hoar and partly settled snow are close to the critical Rayleigh number, therefore a small change in one or more of the snow parameters will decide whether there is convective or conductive heat transport. The influence of thermal convection on the mass transport rates of water vapour in snow is computed based on the assumption of the ventilation approach. Although thermal convection occurs more often than previously assumed, its influence amounts only to about 2-3%