Longwave Radiation in Mountainous Areas and Its Influence on the Energy Balance of Alpine Snowfields

Field studies in the Colorado Front Range provide data for calibrating and testing a model that computes incoming longwave radiation in alpine terrain. The model estimates longwave irradiance on the basis of empirical terrain and atmospheric radiance distributions. A statistical analysis of estimated versus observed longwave irradiance indicates no difference between the regression line and a line of one‐to‐one correspondence. Simulations of longwave irradiance to cirque floors within the study area reveal subtle variations that are due to differences in ground slope and the configuration of surrounding ridges. The simulated variations in longwave irradiance are not adequately represented by the commonly employed istoropic approximation. Surrounding rockwalls enhance the energy balance of alpine snowfields by reducing their net longwave loss circa 50% below that of an unobstructed ridge top. The added energy is equivalent to roughly 0.5 m of melt when integrated over an entire snowmelt season.