| Summary: | The salient feature of the snow cover in the lowlands of interior Alaska is its low density. This results from prolonged exposure to steep snow temperature gradients with negligible wind action. Strong surface inversions occur frequently and last for weeks at a time in interior Alaska and decouple the lowest air layer in valley bottoms from the air aloft. The dense surface air layer is still and cold (-30 to -40°C is common) and the shallow (less than 1 m thick) snow pack underlying it is subjected to steep temperature gradients because the snow-soil interface temperature rarely goes below -6°C. This transforms most of the snow pack into depth hoar before spring breakup. The density of this depth hoar is generally less than 0.20 g cm-3 which is significantly less than that observed on the Greenland and Antarctic ice sheets or in Alpine snow packs. The boundary between air in the valley bottoms and the air aloft is often sharp. Above the inversion winds are frequent and the snow in this environment is harder and had surface density values in the range of 0.35 to 0.40 g cm-3 whereas the density of the entire snow pack in valley bottoms, only 200-300 m below, is about 0.20 g cm-3. Towns in lowland valleys, such as Fairbanks, lie in the stagnant inversion layer and are subject to air pollution in the winter. The snow cover can be utilized to measure this pollution because it acts as a gigantic filter for fallout particles. A simple measure of impurities in snow is obtained by measuring the specific electrical conductance of its melt water. Tests on a network of top-to-bottom samples of the snow pack taken just before breakup during each of three years, in and around Fairbanks, show values which increase sharply from less than 10 µmho cm-1 in outlying areas to greater than 100 µmho cm-1 downtown. Since this is a reconnaissance study a chronological summary of the field work is presented with the results. Supported from USA CRREL Grant DA ENG-27-021-62-G4 and State of Alaska Funds. Preface – Table of Contents – ...
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