The Oklahoma Mesonet provides the spatial density to measure synoptic and mesoscale features. With such resolution, the spatial and temporal variability of surface fluxes can be monitored as well. Because of the highly variable nature of surface energy fluxes, a dense surface network is required. Approximately one-half of the Mesonet sites already measure air temperature and wind speed at two levels from which sensible heat flux has been estimated. Variations of heat flux can be observed in real-time while archived data can provide seasonal and annual trends. Moreover, flux variability across Oklahoma can be correlated with other meteorological or surface variables (e.g., solar radiation, precipitation, and soil moisture).
The Oklahoma Atmospheric Surface-layer Instrumentation System (OASIS) Project is designed to equip the Mesonet with the capability to estimate the total surface energy budget at approximately 90 of the 114 sites across the state. Net radiation will be measured directly using a low maintenance, nonaspirated net radiometer installed at 2 m. Ground heat flux will be measured directly using an average of two heat flux plates installed at 5 cm; the 0-5 cm storage term will be included by measuring the integrated soil temperature over that depth. Soil moisture at 5 cm will be included in the storage term as well. Temperature and wind speed, measured at two levels, allows sensible heat flux to be estimated at all sites with a gradient aerodynamic approach. Latent heat flux will be estimated as the residual from the energy balance equation. As verification of these techniques, approximately nine “Super Sites” also will measure sensible and latent heat directly using an eddy correlation system. Each “Super Site” will be equipped with a sonic anemometer, fast response hygrometer, and a four-way net radiometer. In addition, soil temperature and soil moisture probes will be installed at 54 additional sites across the Mesonetwork.
To ensure data quality and accuracy of the flux estimates, the OASIS instrumentation and methodologies are being compared with a number of independent networks. During the summer of 1998, the NCAR ASTER facility was collocated with the OASIS Mesonet site in Norman, OK. Direct comparisons of OASIS instrumentation and methods during a six week period allowed for a critical evaluation and improvement of the upgraded system. The NCAR Flux-Pam stations will be used during 1999, if possible, for further assessment of the accuracy of surface fluxes. In addition, two Mesonet sites are collocated with ARM sites at Foraker and El Reno, OK. Measurements at these two sites will provide direct comparisons between net radiation, ground, sensible, and latent heat fluxes on a continous basis. Development and installation of the OASIS Project system is scheduled for completion by 1 May 1999. Testing and evaluation of the network will continue through 1 February 2000