Closure of the Surface Energy Budget

Jerald A. Brotzge

 Uversity of Oklahoma
Center for Analysis and Prediction of Storms


The OASIS Project became operational 1 January 2000 and permits measurement of net radiation and ground heat flux as well as sensible and latent heat fluxes via eddy correlation at ten Mesonet sites across Oklahoma. Unfortunately, measurements using eddy correlation (EC) systems often have failed to close the surface energy budget (Rn  <> H + Le + G). Previous experiments such as FIFE, Monsoon-90, and SGP-97 have consistently underestimated closure. This lack of closure casts doubt on the accuracy of EC measurements. In this research, the closure issue is investigated using over 5 million observations collected during a one-year period from the OASIS and ARM projects. Problems with closure were found limited to measurement of latent heat flux, and several reasons for the underestimate in latent heat flux were identified. Instrument error, a mismatch in source area, surface heterogeneity, and fetch are examined as possible sources of error.