Uversity of Oklahoma
Center for Analysis and Prediction of Storms
Abstract:
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.