10/30/2012
Mountain Topography Affects Surface Solar Radiation
Summary
In climate models, radiation from the sun’s rays are assumed to
only interact with the Earth’s surface straight up and down. However, when there is steep topography, as in mountainous regions, a 3D scheme may be needed to capture the impacts on mountain climates. Researchers have now implemented a parameterization of the interactions between 3D radiative transfer and mountain topography in a regional climate model that includes a detailed land surface model. The parameterization accounts for deviations of the downward solar fluxes from flat surfaces. U.S. Department of Energy scientists at Pacific Northwest National Laboratory and at the University of California—Los Angeles investigated the effects of 3D radiative transfer over a western U.S. region focusing on the Sierra Nevada
Mountains. Two simulations, with and without the 3D radiative transfer parameterizations, were performed. Comparison of the simulations shows that mountain topography can induce up to -50 W/m2 to +50 W/m2 deviations in solar fluxes reaching the surface in the Sierra Nevada Mountains. In response to these changes, surface temperature can increase by up to 1oC on the sunny side of the mountains, leading to
enhanced snowmelt and increased soil moisture. The team found that
mountain areas receive more solar radiation during early morning and
late afternoon with a corresponding increase in surface temperature.
However, the 3D-radiation impact is smaller in the middle of the day
leading to a relative 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 the implications to the hydrological cycle in mountainous regions worldwide.
References
Gu, Y., K. N. Liou, W.-L. Lee, and R. L. Leung. 2012. “Simulating 3-D Radiative Transfer Effects over the Sierra Nevada Mountains Using WRF,” Atmospheric Chemistry and Physics 12 , 9965–76. DOI: 10.5194/acp-12-9965-2012.