CAPT Analysis of Land-Atmosphere Interactions Manifested in ARM Observations at the U.S. Southern Great Plains Site

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Description

This study examines land-atmosphere interactions observed during 1997-2008 warm seasons at the ARM Southern Great Plains Central Facility (SGP CF) near Lamont, Oklahoma. Characteristics of the local land-atmosphere coupling are inferred by analyzing the covariation of selected surface and atmospheric variables. For both the energetic and hydrological aspects of this coupling, it is found that atmospheric forcings generally predominate, with comparatively weak feedbacks of the land on the atmosphere occurring much of the time. The diminished land feedbacks are manifested by 1) the inability of soil moisture to comprehensively impact the coupled land-atmosphere energetics, and 2) the limited local recycling of precipitation under synoptic conditions where most of the rainfall derives from remotely triggered convective cells. However, a relative strengthening of land feedbacks is typically observed to occur as the soil dries out in the aftermath of precipitation events, or on days when shallow cumulus clouds (indicative of moist thermal updrafts driven by surface sensible heating) are present. Some implications of these observational results for Community Atmosphere Model hindcasts implemented by the CAPT* project also are considered. *CAPT: Cloud-Associated Parameterization Testbed Acknowledgments This work was funded by the U.S. Department of Energy Office of Science and was performed at the Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.