A clear sky net radiation model for the high-elevation glacial environment

A surface net radiation model appropriate to the high elevation glacial environment has been developed and tested for conditions of clear skies. For three glaciers of differing elevation and physical setting, the model evaluates the direct, diffuse, global, reflected and net shortwave radiation as well as the incoming, emitted and net longwave radiation. These irradiances are combined to produce the surface net radiation. The effect of the surrounding terrain is incorporated by evaluating the reflected shortwave and emitted longwave to the glacier surface from sectors of the terrain, each 45;Two of the glaciers, the Quelccaya Ice Cap and Glaciar Yanamarey are located in Peru. The third, Collier Glacier is located in the continental United States. The summit elevation of Quelccaya is 5,600 meters and is free of horizon obstructions. Glaciar Yanamarey and Collier Glacier are entrenched alpine glaciers with average elevations of 4,300 m and 2,500 m respectively. The shortwave generator follows the model of Davies, Schertzer and Nunez (1975). For longwave estimates, atmospheric emissivities are entered directly or estimated following Marks and Dozier (1979). A time-dependent temperature forcing function is used in estimates of incoming and emitted longwave radiation.;Results indicate that, with calibration, the model produces correlation coefficients of 0.97 or better for instantaneous values of all radiation budget components except the reflected solar radiation. Modeled daily totals reproduce observed values of the incoming fluxes and emitted radiation to within 4% for Quelccaya and 6 to 10% for Collier and Yanamarey. Minimum observed atmospheric emissivities are 0.59 for Quelccaya. Estimated emissivities were slightly smaller than observed values. For Collier Glacier and Yanamarey, reflected shortwave radiation is less than 3% of the global radiation, even with large terrain view factors. For inclined surfaces, receptor slope and azimuth are equally important as terrain configuration in influencing the flux receipt at the surface. An enhancement of 15% can be expected in the incoming longwave due to terrain emittance.