Quantitative Analysis of Terrain Reflected Solar Radiation in Snow-Covered Mountains: A Case Study in Southeastern Tibetan Plateau

Terrain reflected solar radiation in snow-covered mountains is nonnegligible in investigations of the energy budget. However, it has so far not been investigated thoroughly, especially with regard to the influence of snow cover. Several parameterization approaches have been raised but not yet evaluated in a more uniform and quantitative manner. Based on the three-dimensional (3-D) ray-tracing simulation, we explored the temporal and spatial characteristics of the terrain reflected radiation in 15 domains on the southeastern Tibetan Plateau, and comprehensively evaluated different parameterization approaches. The results indicate that the ratio of reflected radiation to total daily radiation ranges from 0.25% to 10.85% at the scale of 5 x 5 km(2) in a winter clear day, and it is 57% higher at noon in spring and autumn due to the higher snow cover fraction. Snow cover not only enhances the magnitude of reflected radiation by increasing surface albedo but also changes the spatial distribution pattern of radiation in partial snow-covered mountains, causing more snow-reflected radiation to be received by the surrounding surfaces. Three forms of terrain configuration factors in common parameterization approaches were evaluated by the ray-tracing model. The complementary of sky view factor shows good consistency with ray-tracing model at domain-averaged scales, with a root mean square error (RMSE) of 2.55 (14%) W/m(2), while the other two both underestimate the radiation. The parameterization approach involving the multi-reflection shows better performance with the normalized RMSE decreasing by 5%. However, the uncertainty of it increases with the surface spatial heterogeneity caused by the partial snow cover, especially at high resolution.

Automated summary

The research found that reflected radiation in snow-covered mountain terrain has a significant impact on the total daily radiation, with the influence being greater in areas with snow cover. Through ray-tracing modeling, different parameterization methods were evaluated for simulating reflected radiation, showing varying degrees of accuracy and limitations in considering surface spatial heterogeneity.