Abstract:

We developed a 3D Monte Carlo photon tracing program for the transfer of radiation in inhomogeneous and irregular terrain to calculate broadband solar and thermal infrared fluxes. We selected an area of 100 × 100 km² in the Tibetan Plateau centered at Lhasa city and used the albedo and surface temperature from MODIS/Terra for this study. We showed that anomalies of surface solar fluxes with reference to a flat surface can be as large as 600 W/m², depending on time of day, mountain configuration, and albedo. Surface temperature is the dominating factor in determining anomalies of the surface infrared flux distribution relative to a flat surface with values as high as 70 W/m² at cold mountain surfaces. The average surface solar flux over regional domains of 100 × 100 km² and 50 × 50 km² comprising intense topography can deviate from the smoothed surface conventionally assumed in climate models and GCMs by 10–50 W/m².

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