30 research outputs found
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Comparison of precipitable water vapor measurements obtained by microwave radiometry and radiosondes at the Southern Great ...
Comparisons between the precipitable water vapor (PWV) estimated by passive microwave radiometers (MWRs) and that obtained by integrating the vertical profile of water vapor density measured by radiosondes (BBSS) have generally shown good agreement. These comparisons, however, have usually been done over rather short time periods and consequently within limited ranges of total PWV and with limited numbers of radiosondes. We have been making regular comparisons between MWR and BBSS estimates of PWV at the Southern Great Plains Cloud and Radiation Testbed (SGP/CART) site since late 1992 as part of an ongoing quality measurement experiment (QME). This suite of comparisons spans three annual cycles and a relatively wide range of total PWV amounts. Our findings show that although for the most part the agreement is excellent, differences between the two measurements occur. These differences may be related to the MWR retrieval of PWV and to calibration variations between radiosonde batches
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Initial evaluation of profiles of temperature, water vapor, and cloud liquid water from a new microwave profiling radiometer.
To measure the vertical profiles of temperature and water vapor that are essential for modeling atmospheric processes, the Atmospheric Radiation Measurement (ARM) Program of the U. S. Department of Energy launches approximately 2600 radiosondes each year from its Southern Great Plains (SGP) facilities in Oklahoma and Kansas, USA. The annual cost of this effort exceeds $500,000 in materials and labor. Despite the expense, these soundings have a coarse temporal resolution and reporting interval compared with model time steps. In contrast, the radiation measurements used for model evaluations have temporal resolutions and reporting intervals of a few minutes at most. Conversely, radiosondes have a much higher vertical spatial resolution than most models can use. Modelers generally reduce the vertical resolution of the soundings by averaging over the vertical layers of the model. Recently, Radiometries Corporation (Boulder, Colorado, USA) developed a 12-channel, ground-based microwave radiometer capable of providing continuous, real-time vertical profiles of temperature, water vapor, and limited-resolution cloud liquid water from the surface to 10 km in nearly all weather conditions. The microwave radiometer profiler (MWRP) offers a much finer temporal resolution and reporting interval (about 10 minutes) than the radiosonde but a coarser vertical resolution that may be more appropriate for models. Profiles of temperature, water vapor, and cloud liquid water are obtained at 47 levels: from 0 to 1 km above ground level at 100-m intervals and from 1 to 10 km at 250-m intervals. The profiles are derived from the measured brightness temperatures with neural network retrieval. In Figure 1, profiles of temperature, water vapor, and cloud liquid water for 10 May 2000 are presented as time-height plots. MWRP profiles coincident with the 11:31 UTC (05:31 local) and 23:47 UTC (17:47 local) soundings for 10 May are presented in Figures 2 and 3, respectively. These profiles illustrate typical performance for temperature inversion and lapse conditions
Analysis of Raman Lidar and radiosonde measurements from the AWEX-G field campaign and its relation to Aqua validation
Early work within the Aqua validation activity revealed there to be large differences in water vapor measurement accuracy among the various technologies in use for providing validation data. The validation measurements were made at globally distributed sites making it difficult to isolate the sources of the apparent measurement differences among the various sensors, which included both Raman lidar and radiosonde. Because of this, the AIRS Water Vapor Experiment-Ground (AWEX-G) was held in October - November, 2003 with the goal of bringing validation technologies to a common site for intercomparison and resolution of the measurement discrepancies. Using the University of Colorado Cryogenic Frostpoint Hygrometer (CFH) as the water vapor reference, the AWEX-G field campaign resulted in new correction techniques for both Raman lidar, Vaisala RS80-H and RS90/92 measurements that significantly improve the absolute accuracy of those measurement systems particularly in the upper troposphere. Mean comparisons of radiosondes and lidar are performed demonstrating agreement between corrected sensors and the CFH to generally within 5% thereby providing data of sufficient accuracy for Aqua validation purposes. Examples of the use of the correction techniques in radiance and retrieval comparisons are provided and discussed
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Performance of radar wind profilers, radiosondes, and surface flux stations at the SGP CART site
The performance of several routinely operating observational systems at the Southern Great Plains (SGP) Cloud and Radiation Testbed (CART) site has been evaluated. The results of a few specific investigations are shown here for Radar Wind Profilers (RWPs) and Radio Acoustic Sounding Systems (RASSs), Balloon-Borne Sounding Systems (BBSSs), and Energy Balance Bowen Ratio (EBBR) stations
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An evaluation of ARM radiosonde operational performance
Because the ARM (Atmospheric Radiation Measurement) program uses data from radiosondes for real-time quality control and sensitive modeling applications, it is important to have a quantitative measure of the quality of the radiosonde data themselves. Two methods have been tried for estimating the quality of radiosonde data: comparisons with known standards before launch and examination of pseudo-replicate samples by single sensors aloft. The ground check procedure showed that the ARM radiosondes are within manufacturer`s specifications for measuring relative humidity; procedural artifacts prevented verification for temperature. Pseudo-replicates from ascent and descent suggest that the temperature measurement is within the specified {minus_plus}0.2 C. On average ascent and descent data are similar, but detailed structure may be obscured on descent by loss of sampling density, and the descent involves other uncertainties
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An iterative procedure for estimating areally averaged heat flux using planetary boundary layer mixed layer height and locally measured heat flux
Measurements at the central facility of the Southern Great Plains (SGP) Cloud and Radiation Testbed (CART) are intended to verify, improve, and develop parameterizations in radiative flux models that are subsequently used in General Circulation Models (GCMs). The reliability of this approach depends upon the representativeness of the local measurements at the central facility for the site as a whole or on how these measurements can be interpreted so as to accurately represent increasingly large scales. The variation of surface energy budget terms over the SGP CART site is extremely large. Surface layer measurements of the sensible heat flux (H) often vary by a factor of 2 or more at the CART site (Coulter et al. 1996). The Planetary Boundary Layer (PBL) effectively integrates the local inputs across large scales; because the mixed layer height (h) is principally driven by H, it can, in principal, be used for estimates of surface heat flux over scales on the order of tens of kilometers. By combining measurements of h from radiosondes or radar wind profiles with a one-dimensional model of mixed layer height, they are investigating the ability of diagnosing large-scale heat fluxes. The authors have developed a procedure using the model described by Boers et al. (1984) to investigate the effect of changes in surface sensible heat flux on the mixed layer height. The objective of the study is to invert the sense of the model
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Long-term evapotranspiration estimates in the Walnut River Watershed in Kansas.
This project focuses on improving and testing a simple method for using reflectance data obtained from satellites to infer the effects on evapotranspiration of variations in soil moisture availability. The major advantage to the method, which is based on the parameterization of subgrid-scale surface fluxes (PASS) model (Gao 1995; Gao et al. 1998), is that it can be applied to areas having diverse surface characteristics where direct surface flux measurements either do not exist or are not feasible and where meteorological data are available from only a limited number of ground stations. The emphasis of the PASS model is on improving (1) methods for using high-resolution satellite remote sensing data to derive the essential parameters for individual types of surfaces overlarge areas, (2) algorithms for describing the interactions of near-surface atmospheric conditions with surface processes, and (3) algorithms for computing surface energy and water vapor flux at a scale close to the size of a satellite pixel. An operational modeling system is being developed. Testing of the system is accomplished by applying it to the Walnut River Wak-shed (WRW), instrumented watershed of moderate area (5,000 km{sup 2}) located just east of Wichita, Kansas. Data from field experiments such as the intensive field campaign in 1997 by the Cooperative Atmosphere-Surface Exchange Study (CASES) and from routine operation of the Atmospheric Boundary Layer Experiments (ABLE) in the WRW are used to evaluate the ability of the PASS model to estimate accumulated water loss over a growing season. The research goals of the project areas follow: (1) Improve the existing satellite-data interfacing modules, especially the parameterization of soil moisture availability and water vapor flux; (2) Apply and evaluate the methods by using measurements at ground stations distributed within the WRW; and (3) Develop an operational version of the modeling system, and apply it to derive long-term evapotranspiration estimates at the WRW