3.3
Closure of the surface energy budget at 10 OASIS super sites
Jerald A. Brotzge, University of Oklahoma, Norman, OK; and K. C. Crawford
A historical review of the literature confirms a pattern of underestimating the sum of sensible and latent heat flux (SH+LH) by eddy correlation (EC) when compared to the net available energy of net radiation and ground heat flux (Rn – GH). An underestimation in (SH+LH) leads to an underestimation in closure as defined as C=(SH+LH)/(Rn-GH). Results from FIFE, Monsoon-90, HAPEX-SAHEL, and SGP-97 reflect an underestimation in closure from EC observations.
During 1999 the Oklahoma Atmospheric Surface-layer Instrumentation System (OASIS) Project instrumented 10 Oklahoma Mesonet sites with the capability to monitor the entire surface energy budget in real-time. A four-component net radiometer, the CNR1, measures incoming and outgoing shortwave and longwave radiation, and ground heat flux is estimated from a suite of in-ground sensors. A sonic anemometer and Krypton hygrometer, sampling at 8 Hz, provide measurements of sensible and latent heat flux, respectively. Observations of each component are averaged and recorded every 5-minutes.
A complete one-year data set of surface energy budget measurements collected from the ten OASIS sites are examined in detail. The OASIS data set yields similar results to previous work with a consistent underestimation in closure. Daily estimates of closure range between 70% and 92% at the ten sites. A brief synopsis of closure is presented followed by several hypotheses as to the reasons for the underestimation. Results focus upon the effects of topography, vegetation, and instrument error.
Session 3, Surface Energy Fluxes
Monday, 15 January 2001, 1:30 PM-3:00 PM
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