October 2012

Accounting for Mountain Topography in Climate Models

3D simulation shows mountain impacts on surface solar fluxes.

Click to enlarge photo. Enlarge Photo

Image courtesy of Wikimedia Commons, Geographer

To better understand solar radiation effects in mountainous regions, scientists have incorporated three-dimensional inputs into climate simulations examining the Sierra Nevadas, including Mount Whitney (pictured).

The Science

In climate models, radiation from the sun’s rays is assumed to interact with Earth’s surface only straight up and down. However, for regions with steep topography, including mountains, a three-dimensional (3D) scheme may be needed to capture how radiation affects the climate in such areas.

The Impact

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.

Summary

Scientists at the Department of Energy’s (DOE) Pacific Northwest National Laboratory and 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 were performed: one with 3D radiative transfer parameterizations and one without. Comparison of the simulations shows that mountain topography can induce up to ± 50 W/m2 deviations in solar fluxes reaching the surface in the Sierra Nevadas. In response to these changes, the 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 during midday, leading to a relative cooling effect. These changes are reflected in a reduced diurnal temperature range as well as shifts in sensible and latent heat fluxes. The relatively large changes in diurnal variability and surface fluxes underscore the need to assess the climatic effects of 3D radiative transfer in mountains and the implications to the hydrological cycle in mountainous regions worldwide.

Contact

Y. Gu
Joint Institute for Regional Earth System Science and Engineering
Department of Atmospheric and Oceanic Sciences, University of California
Los Angeles, CA 90095
gu@atmos.ucla.edu

Funding

This research was supported by the Earth System Modeling program (grant DESC0006742) within DOE’s Office of Science Biological and Environmental Research program

Publications

Gu, Y., Liou, K.N., Lee, W.L., and Leung, R.L. “Simulating 3-D radiative transfer effects over the Sierra Nevada mountains using WRF.” Atmos. Chem. Phys. 12, 9965–9976 (2012). [DOI: 10.5194/acp-12-9965-2012].

Highlight Categories

Program: BER, CESD

Performer/Facility: University, DOE Laboratory

Last modified: 9/16/2013 7:14:48 AM