Two Theoretical Models of Radiation Heat Transfer Between Forest Trees and Snowpacks
Two simple theoretical models describe the effect of forest cover on radiation transfer to a snowpack: Model 1, which describes the effect of varying canopy closure on the net radiation received by an interior snowpack, suggests that the net radiation may increase or decrease monotonically as the canopy closure increases from zero to 100%, or may exhibit a maximum at a non-zero canopy closure depending upon whether or not certain conditions are satisfied. This perhaps surprising result was due to the combined effect of long-wave radiation emitted from the canopy to the snowpack and multiple reflections of solar radiation between the snowpack and canopy. Model 2 predicts the spatial variation of the long-wave radiation flux from the bole and crown of an individual tree to the surrounding snowpack. This model may partially explain melt rates which appear to be higher near the boles of trees. Calculations with assumed data showed an intensification of the long-wave radiation flux to the snowpack as the bole is approached. According to this model, a horizontal snow surface receives negligible amounts of long-wave radiation from the tree at distances from the bole that are greater than two to three times the crown radius.