01/28/2014
Observational Analysis of Land-Atmosphere Coupling Provides Standards for Evaluating Climate Models
Summary
Global climate model simulations of northern-hemisphere summer climate imply that soil moisture couples strongly with precipitation and other atmospheric variables in semi-arid regions such as the U.S. Southern Great Plains (SGP). The long-time dataset from the Atmospheric Radiation Measurement (ARM) SGP site near Lamont, Oklahoma, provided the data to evaluate these model predictions. In this study, U.S. Department of Energy (DOE) researchers at Lawrence Livermore National Laboratory estimated the strength of land-atmosphere coupling from correlations of soil moisture with a diverse set of atmospheric variables observed during the summers of 1997-2008 at the SGP site. Local soil moisture correlated significantly with surface evaporation, relative humidity, and temperature, as well as with the base heights of clouds in the atmospheric boundary layer. These correlations grew stronger as the soil increasingly dried out in the aftermath of precipitation events. Contrary to the climate model predictions, no significant correlation of soil moisture with subsequent precipitation events was found, indicating that the coupling between local soil conditions and precipitation initiation is too strong in the climate models. Further evaluation and development of the models’ land-surface and boundary layer parameterizations are needed to identify and address the specific reasons for these discrepancies. The datasets of observed characteristics of SGP land-atmosphere coupling developed in this study will provide a basis for future diagnosis and improvement of the climate model parameterizations using a testbed framework developed by DOE researchers.
References
Phillips, T. J., and S.A. Klein. 2014. “Land-Atmosphere Coupling Manifested in Warm-Season Observations on the U.S. Southern Great Plains,” Journal of Geophysical Research—Atmospheres 119(2), 509-28. DOI:10.1002/2013/D020492.