Analysis of Cold Airmass Temperature Modification across the U.S. Great Plains as a Consequence of Snow Depth and Albedo

Abstract

The presence of snow cover has been shown to modify atmospheric conditions through much of the earth?s troposphere due to its radiative effects. Snow cover has garnered much attention in recent decades as a result of concerns associated with potential changes in the global environment that may be intensified by the presence or absence of a snow cover. As a result, a greater emphasis has been placed on the representation of snow cover in weather and climate prediction models. This study investigates the effects of snow albedo and snow depth on the modification of surface air temperatures within cold air masses moving across the U.S. Great Plains in winter. Through the adaptation of a one-dimensional snowpack model, the thermal characteristics of the core of a cold air mass were derived from the equation governing the heat balance between the surface and the lower atmosphere. The methodology was based on the premise that the core of a cold air mass may be considered homogeneous and not subject to advection of air from outside, thereby isolating the exchange of energy between the surface and the atmosphere as the control on lower-tropospheric temperatures. The adapted model included the synergism of the air mass?snow cover relationship through time, incorporating the natural feedback process. Simulation of surface air temperatures within four cold air masses over snow cover of different albedo values and depths led to several conclusions. In testing the effects of snow albedo, results indicate 1) mean daytime air temperatures 3°?6°C higher and maximum daytime air temperatures 7°?12°C higher over snow with an albedo equal to 0.50 compared to 0.90, as a consequence of differences in sensible heat flux, and ultimately, absorbed solar radiation, and 2) little thermal inertia and therefore little difference in subsequent nighttime airmass temperatures over snow with an albedo of 0.50 compared to 0.90. In testing the effects of snow depth, results indicate 1) little difference in daytime air temperatures associated with a snow depth of 2.5 cm compared to 15.0 or 30.0 cm, 2) an increase in mean nighttime temperatures of 0.2°?0.7°C over a snow depth of 2.5 cm compared to either of the larger depths, and 3) a masking of the underlying bare soil surfaces by the snow depths of 15.0 and 30.0 cm and virtually no difference in airmass temperatures over the two snow depths. The potential utility of the results of this study lies in their application as additional guidance for temperature forecasts within wintertime cold air masses over, and downstream from, snow cover across the U.S. Great Plains. Likewise, this study illustrates the importance of the various components of the heat balance between the lower atmosphere and snow cover as based on the physical characteristics of the snowpack, which could prove beneficial in considerations of snow cover in weather and climate models.