INFILTRATION OF WATER INTO SNOW

Measurements from a rectangular grid of thermistors set in a maritime snowpack are used to study the infiltration of water during two midwin ter rain on snow events. The progress of wetting is tracked in real ti me by monitoring changes in the position of the zero-degree isotherm. Rates and patterns of infiltration are calculated for each event. Infi ltration was not uniform, and water penetrated through localized chann els that often occupied less than 50% of the total volume of the snowp ack. The evolution of wetting was strongly influenced by the snow stra tigraphy. In one case the snowpack contained multiple ice layers, and vertical flow was impeded and diverted laterally for several hours at each layer. In the other case the snowpack was more homogeneous, and w ater concentrated in channels and penetrated to depth more rapidly. Th e measurements of temperature are also used to calculate the component s of heat transfer within the snow during each rain event. Heat transf er in dry snow occurs primarily by conduction, and rates are relativel y slow. However, introduction of liquid water results in the release o f latent heat when water freezes on contact with subfreezing snow at t he wetting front. The release of latent heat dominates heat transfer a nd has the potential to warm the snowpack rapidly. Rates of freezing n eeded to satisfy the heat equation are calculated. In both cases studi ed, less than 4% of the total influx of rainwater needed to change pha se. Most of the rain remained liquid and wet the snow or drained throu gh the snowpack.