Effects of 3D Radiative Transfer in the Sierra Nevada Mountains
Researchers have now implemented a parameterization of the interactions between 3D radiative transfer and mountain topography in a regional climate model based on the Weather Research and Forecasting (WRF) model, which includes a detailed land surface model. The parameterization accounts for the deviations of the downward solar fluxes from flat surfaces. The researchers, including DOE scientists at Pacific Northwest National Laboratory (PNNL), investigated the effects of 3D radiative transfer over a western U.S. region with a focus on the Sierra Nevada mountains. Two simulations, with and without the 3D radiative transfer parameterizations, were performed for a case study of a relatively clear day in the spring season. Comparison of the simulations shows that mountain topography can induce up to – 50 W/m2 and 50 W/m2 deviations in solar fluxes reaching the surface in the Sierra Nevada mountains. In response to the changes in downward solar fluxes, surface temperature can increase by up to 1oC in the sunny side of the mountains, leading to enhanced snowmelt and increased soil moisture. The team found mountain areas receive more solar radiation during early morning and late afternoon with a corresponding increase in surface temperature. However, solar insolation reduces in the middle of the day leading to a cooling effect. These changes are reflected in a reduced diurnal temperature range and changes in sensible and latent heat fluxes. The relatively large changes in diurnal variability and surface fluxes motivate the need to assess the climatic effects of 3D radiative transfer in mountains and implications to the hydrological cycle in mountainous regions worldwide. This research is a collaborative effort between scientists at the University of California Los Angeles and PNNL.