An Assessment of the Accuracy of Profile Sensible Heat Flux Measurements from the OASIS Project using the NCAR Flux-PAM Network

The OASIS (Oklahoma Atmospheric Surface-Layer Instrumentation System) Project is a National Science Foundation, Major Research Instrumentation grant to add observational capabilities to the Oklahoma Mesonet by developing a relatively low cost, low power, low maintenance observing system to monitor the surface energy budget in real time. This 90 station network estimates sensible heat flux (SH) using an indirect method based on Monin-Obukhov similarity theory, measures ground heat flux (GH), and measures net radiation (Rn) using a low-cost net radiometer; latent heat flux (LH) is estimated as the residual of the energy budget: Rn=SH + LH + GH. Ten of the 90 sites are equipped with additional instrumentation to directly measure sensible and latent heat fluxes using eddy covariance techniques, with net radiation being measured using a 4-component net radiometer.

OASIS2000 was the second phase of data evaluation for the OASIS Project. The first phase, OASIS98, conducted in the summer of 1998, was used to determine the accuracy with which OASIS instrumentation could measure/estimate the components of the surface energy budget. NCAR’s Integrated Surface Flux Facility (ISFF), formerly know as ASTER, was used as a reference for measurement comparison. Results from OASIS98 revealed that OASIS instrumentation was sufficiently accurate to proceed with the next phase of the project, station installation.

The purpose of the OASIS2000 field project was to utilize the NCAR ISFF FLUX-PAM facilities to provide an estimate of the flux measurement errors at OASIS-instrumented Mesonet sites. Six to nine FLUX-PAM towers were collocated with 33 of the 90 OASIS-instrumented Mesonet sites for approximately four weeks. Project duration was 21 February to 30 June 2000. This paper will show results from the OASIS2000 field project, focusing on an evaluation of the accuracy of profile sensible heat flux measurements made at individual Mesonet sites over a variety of climate and topographic regimes.