Submitted to: Journal of Applied Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 22, 1998
Publication Date: N/A
Interpretive Summary: Surface temperature and meteorological observations collected during the Washita '94 Experiment were used in a model for computing evapotraspiration (ET) from natural and agricultural surfaces. The "local" meteorological data were collected at two meters from weather towers while "regional" meteorological data were collected from balloon borne instruments rising 1000's of meters above the surface. There was less agreement between modeled and measured ET when the regional versus local meteorological data were used for driving the model. However, differences with the ET observations ranged from 25% to 30%, on average, which is similar to the uncertainty in ET observations. This permits the mapping of spatially-distributed ET over large area scales using a single observation of upper air data. This will be especially useful when the model is applied operationally to high resolution surface temperature data which will be available from the ASTER instrument on NASA's Earth Observing System. This approach with ASTER data will permit high resolution ET mapping over agricultural regions and provide useful information to resource managers on plant stress and water use of various agricultural and natural ecosystems.
Technical Abstract: Surface temperature and meteorological observations collected during the Washita '94 Experiment were used in a two-source energy balance model for computing fluxes from natural and agricultural surfaces. Standard surface layer similarity was used with the "local" meteorological data while bulk similarity approaches were used with mixed-layer data. This latter approach to drive model computations for the different sites is similar to the so-called flux aggregation schemes or methods proposed to account for sub-grid variability in atmospheric models. There was less agreement between modeled and measured fluxes when using mixed-layer versus local meteorological data for driving the model. Differences between the flux observations using local data were 25% on average, while using the mixed layer data with bulk formation differences averaged 30%. Given the uncertainty in flux observations is around 20%, these estimates are still considered reasonable. Moreover, they permit the mapping of spatially distributed surface fluxes at regional scales using a single observation of the upper atmosphere with high resolution surface temperature data. Such surface temperature observations will be available from ASTER to be launched on NASA's Earth Observing System.