A planetary boundary layer observational capability in Kansas

An initiative is underway to establish the Argonne Boundary Layer Experiments (ABLE) facility to provide continuous, long-term observations of the planetary boundary layer (PBL) with state-of-the-art instruments. Planning for ABLE began during 1995, and implementation is expected to be mostly complete by 1998. ABLE will be located within the area now occupied by the Southern Great Plains (SGP) Cloud and Radiation Testbed (CART) site of DOE`s Atmospheric Radiation Measurement (ARM) program. The Argonne facility will concentrate on measuring at spatial scales considerably smaller than addressed with CART. When it is fully functional, ABLE will offer atmospheric scientists the opportunity to remotely {open_quote}collect{close_quote} data in real time without necessarily leaving their home offices. Specialized computer analysis and visualization software will be developed and provided by ABLE to facilitate analysis by remote users. ABLE will host specialized field campaigns for which it can provide supplementary measurements and the required facilities for shorter-term instrument deployments. In addition, ABLE will function as the proving ground for new technologies for atmospheric boundary layer research. 1 ref., 1 fig

Aspects of the quality of data from SGP cart site broadband radiation sensors

This report presents details of the performance of broadband radiometers the the southern Great Plains (SGP) cloud and radiation testbed (CART) site to estimate the uncertainties of irradiance observations. Net radiation is observed with net radiometer in the energy balance Bowen ratio station at the central facility and compared with the net radiation computed as the sum of component irradiances recorded by nearby pyranometers and pyrgeometers. This paper observes the uncertainties of readings from net radiometers which are known to be substantial

Estimating watershed evapotranspiration with PASS. Part II: moisture budgets during drydown periods

The second part of the parameterization of subgrid-scale surface fluxes model (PASS2) has been developed to estimate long-term evapotranspiration rates over extended areas at a high spatial resolution by using satellite remote sensing data and limited, but continuous, surface meteorological measurements. Other required inputs include data on initial root-zone available moisture (RAM) content computed by PASS1 for each pixel at the time of clear-sky satellite overpasses, normalized difference vegetation index (NDVI) from the overpasses, and databases on available water capacity and land-use classes. Site-specific PASS2 parameterizations evaluate surface albedo, roughness length, and ground heat flux for each pixel, and special functions distribute areally representative observations of wind speed, temperature, and water vapor pressure to individual pixels. The surface temperature for each pixel and each time increment is computed with an approximation involving the surface energy budget, and the evapotranspiration rates are computed via a bulk aerodynamic formulation. Results from PASS2 were compared with observations made during the 1997 Cooperative Atmosphere–Surface Exchange Study field campaign in Kansas. The modeled diurnal variation of RAM content, latent heat flux, and daily evapotranspiration rate were realistic in comparison to measurements at eight surface sites. With the limited resolution of the NDVI data, however, model results deviated from the observations at locations where the measurement sites were in fields with surface vegetative conditions notably different than surrounding fields. Comparisons with aircraft-based flux measurements suggested that the evapotranspiration rates over distances of tens of kilometers were modeled without significant bias

Observed effects of horizontal surface temperature variations on the atmosphere over a Mid-west watershed during CASES 97

The association between 10-km scale horizontal variation of radiometric surface temperature (Ts) and aircraft-derived fluxes of sensible heat (H) and moisture (LE) is the focus of this work. We use aircraft, surface, and satellite data from a Cooperative Atmospheric-Surface Exchange Studies (CASES) field program, which took place in the southern part of the 60 100 km Walnut River (Kansas) watershed from 22 April to 22 May 1997, when winter wheat matured and prairie grass greened up. Aircraft Ts observed along repeated flight tracks above the surface layer showed a persistent pattern: maxima over ridges characterized by shallow soil and rocky outcroppings and minima over riparian zones. H and Ts reached maxima in the same longitude zone on two flight tracks 40 km apart. Satellite Ts data from March to June reveal similar persistent patterns with minima more persistent than maxima. Two mechanisms are suggested to explain the association of H and Ts maxima: (1) for winds between 6 and 8 ms 1, modulation of the surface energy budget by vegetation effects; or (2) for winds equal to or below 4 ms 1,a thermally driven circulation centered on Ts maxima. Both mechanisms were possibly enhanced by increased static instability over the Ts maxima. Owing to the small sample available, these results are suggestive rather than conclusive. Effects of rainfall and vegetation on watershed-scale Ts gradients are also explored

Using the ABLE facility to observe urbanization effects on planetary boundary layer processes

The Argonne Boundary Layer Experiments (ABLE) facility, located in south central Kansas, east of Wichita, is devoted primarily to investigations of and within the planetary boundary layer (PBL), including the dynamics of the mixed layer during both day and night; effects of varying land use and landform; the interactive role of precipitation, runoff, and soil moisture; storm development; and energy budgets on scales of 10 to 100 km. With an expected lifetime of 10--15 years, the facility is well situated to observe the effects of gradual urbanization on PBL dynamics and structure as the Wichita urban area expands to the east and several small municipalities located within the study area expand. Combining the continuous measurements of ABLE with (1) ancillary continuous measurements of, for example, the Atmospheric Radiation Measurement (ARM) program and the Global Energy Water Cycle Experiment (GEWEX) programs and with (2) shorter, more intensive studies within ABLE, such as the Cooperative Atmosphere Surface Exchange Studies (CASES) Program, allows hypothesized features of urbanization, including heat island effects, precipitation enhancement, and modification of the surface energy budget partitioning, to be studied