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Land-surface-atmosphere coupling in observations and models

The diurnal cycle and the daily mean at the land-surface result from the coupling of many physical processes. The framework of this review is largely conceptual; looking for relationships and information in the coupling of processes in models and observations. Starting from the surface energy balance, the role of the surface and cloud albedos in the shortwave and longwave fluxes is discussed. A long-wave radiative scaling of the diurnal temperature range and the night-time boundary layer is summarized. Several aspects of the local surface energy partition are presented: the role of soilwater availability and clouds; vector methods for understanding mixed layer evolution, and the coupling between surface and boundary layer that determines the lifting condensation level. Moving to larger scales, evaporation-precipitation feedback in models is discussed; and the coupling of column water vapor, clouds and precipitation to vertical motion and moisture convergence over the Amazon. The final topic is a comparison of the ratio of surface shortwave cloud forcing to the diabatic precipitation forcing of the atmosphere in ERA-40 with observations.

Plain English Discussion

This paper is an illustrated review explaining what determines the climate during the day and at night over forest and grasslands. Sunlight warms the surface but some is reflected, especially if there is snow cover on grass. Clouds and water vapor in the atmosphere trap the earth's heat and reduce the cooling of the surface at night. Rainfall refills the reservoirs of water in the soil, which increases evaporation, giving a cooler surface, more clouds and the likelihood of more rain.

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Betts, A. K. (2009), Land-surface-atmosphere coupling in observations and models. J. Adv. Model Earth Syst., Vol. 1, Art. #4, 18 pp., doi: 10.3894/JAMES.2009.1.4 [Published Online 1 Jul. '09] http://james.agu.org/index.php/JAMES/article/view/v1n4/JAMES.2009.1.4