The OASIS Project: Oklahoma Atmospheric Surface-Layer Instrumentation System
June - July 1998
The objectives of The OASIS Project (Oklahoma Atmospheric & Surface-layer Instrumentation System) are to advance the frontier of mesoscale and storm-scale meteorological research as well as hydrologic, agricultural, and climatological research by:
- Development of a system of surface-flux stations using the 114 operating sites in the Oklahoma Mesonetwork;
- Development of a system of electric-field sensors using the 42 sites in a Micronetwork of stations over the Little Washita watershed (southwest of Oklahoma City).
The foundation of this instrument development project is the Oklahoma Mesonetwork. This network of 114 sites has operated continuously since commissioning in March of 1994. Sites have sensors that extend from 10 m above ground to 75 cm below ground.
The source of funding for The OASIS Project is the National Science Foundation's (NSF) Major Research Instrumentation (MRI) Program. OASIS represents an opportunity to capitalize on the sizable investment and stable operations of the Oklahoma Mesonet by augmentation of its capabilities in three distinct, but related research areas: (1) surface energy budget; (2) vertical flux of heat and moisture, and (3) storm electrification.
The new, unique data sets that result will make it possible to address a number of key questions that cannot be dealt with today for lack of observations. For example, quantitative assessment of the surface energy budget for the entire state will provide better initialization for storm-scale modeling and will allow tests of the relative importance of surface energy fluxes under various conditions. Electric-field data from the network of ground-based sensors will be used to investigate variations in electrical activity from storm-to-storm, and relations of electrical activity to other meteorological observables in storms, such as radar reflectivity.
The two main objectives of the Surface-layer Intercomparison of Fluxes (SIF) Project are:
- Examine the uncertainties associated with the measurement of surface fluxes made in the OASIS Project,
- Validate the reference sensors used at the OASIS intercomparison facility.
ASTER facilities are requested to provide a reference for intercomparison with OASIS-measured fluxes. This will be done by carefully comparing the estimated surface fluxes obtained using OASIS instrumentation with those directly measured by ASTER. Measurement of the following parameters by ASTER are required: momentum, sensible heat, and water vapor fluxes by eddy-correlation; vertical profiles of wind, temperature, and humidity; net radiation, soil heat flux, soil temperature, and soil moisture.
The OASIS intercomparion facility has been developed for the OASIS Project in which high quality reference sensors are being used to verify the accuracy of potential OASIS instrumentation (e.g., high quality 4-way net radiation measurements are being compared with measurements from lower quality, less expensive net radiation sensors). ASTER measurements will be compared with the OASIS reference sensors. In addition, ASTER's ability to measure profiles of temperature, water vapor, humidity, and wind at multiple levels makes it possible to assess the quality of the fetch at the OASIS intercomparison facility. Finally, ASTER's mechanically-aspirated temperature and relative humidity measurements will be compared with naturally-ventilated measurements made by OASIS.
The use of the ASTER facility will make it possible to quantify the accuracy of the measurement methods used by OASIS and allow detailed examination of the errors associated with each energy component.
NCAR ASTER facilities are requested for the six-week period 1 July to 15 Aug 1998.
The use of the ASTER facilities is the first of a two-step process to validate and verify the measurement techniques and the accuracy of the measured fluxes made by OASIS. In the first step described here, ASTER will be used to verify the accuracy of the proposed OASIS instrumentation at the OASIS intercomparison facility. In the second step, flux-Pam will be used to examine the errors in the measured fluxes at individual Mesonet sites (request submitted). Upon completion of the two field projects, OASIS will be poised to provide estimates of the surface energy budget across the entire state of Oklahoma. Without the use of NCAR's ASTER and flux-Pam facilities, it will be difficult to quantify the errors associated with the OASIS flux estimates.
Scott J. Richardson
University of Oklahoma, Oklahoma Climatological Survey
100 East Boyd, Suite 1210
Norman, OK 73019