Impact of 3-D Radiation-Topography Interactions on Surface Temperature and Energy Budget Over the Tibetan Plateau in Winter

We incorporate a parameterization to quantify the effect of three-dimensional (3-D) radiation-topography interactions on the solar flux absorbed by the surfaces, including multiple reflections between surfaces and differences in sunward/shaded slopes, in the Community Climate System Model version 4 (CCSM4). A sensitivity experiment is carried out using CCSM4 with the prescribed sea surface temperature for year 2000 to investigate its impact on energy budget and surface temperature over the Tibetan Plateau (TP). The results show that the topographic effect reduces the upward surface shortwave flux and, at the same time, enhance snowmelt rate over the central and southern parts of TP. Comparing to observations and the ensemble of Coupled Model Intercomparison Project Phase 5 (CMIP5), we found that CMIP5 models have a strong cold bias of 3.9K over TP, partially induced by the strong reflection of shortwave fluxes. We show that the inclusion of topographic effect reduces the substantial biases of upward shortwave fluxes and surface air temperatures over TP by 13% in the CCSM4 model. Plain Language Summary We have developed a program to calculate the impact of shadow and multiple reflections on sunlight absorbed by the surface in mountainous areas for application to climate models. The results show that this impact can increase the amount of solar energy absorbed by the surface and produce a higher temperature. Because no climate model considers this effect currently, we believe it is why most global models severely underestimate the temperature over the Tibetan Plateau.