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Gerard E. Klazura

Abstract

Precipitation particles >250 μ were sampled in the upper regions of warm cumuli over southeast Texas using a foil-belt particle sampler. It was found that relatively high concentrations of drops can occur. Concentrations exceeding 1000 m−3 were found in nearly 25% of the clouds. Drop sizes 1 mm in diameter were found fairly often, and 2-mm drops were occasionally sampled.

The effect of cloud height on the precipitation characteristics was found to be quite pronounced. Higher concentrations and broader distributions generally were found in the tallest clouds. The height of clouds plays a more important role in determining drop concentration and size distribution range than do updrafts or downdrafts.

In a comparison between concentration of precipitation particles and average cloud water content (CWCm), it was found that large quantities of drops were associated with low CWCm. Conversely, large values of CWCm were associated with small numbers of drops >250 μ in diameter.

The 1968 clouds generally contained much higher concentrations of drops and had broader distributions of drop sizes than did the 1969 clouds. Smaller clouds investigated during 1968 were nearly as proficient in developing large drops as much taller clouds studied during 1969. The 1968 clouds seemed to have precipitation particle characteristics that were similar to trade-wind cumuli investigated by Brown and Braham, while the drop characteristics of the 1969 clouds were more nearly like the cumulus congestus studied in Missouri, also by Brown and Braham.

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Gerard E. Klazura

Abstract

Radar and gage data from a convective storm were analyzed with the objective of examining how much gage-estimated and radar-estimated rainfall differ in a high rainfall-rate gradient situation considering 1) the location and size of the radar contributing area, 2) whether radar-estimated rainfall was computed using maximum, average or integrated values, and 3) the radar reflectivity factor threshold. Differences exceeding a factor of 6 and 3 have been observed for individual gages and for the mean of 17 gages, respectively.

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Gerard E. Klazura and Ra Aman

Abstract

This paid describes the logic and process used to process high volumes of digital radar data recorded on magnetic tape to a compressed quality-checked archival format. The basic Philosophy in the processing is to retain all echo data that exceed the background noise threshold, and to convert fixed-length raw data records to a space-saving variab1e-length format, having about 70 data quality conditions checked and flagged in binary masks. Edit flags provide information to analysts regarding errors or potential errors within the header fields (e.g. azimuth, elevation, date, time, range delay, range interval, and samples per averaged return) and data fields (e.g. suspicious reflectivity gradients, anomalously high reflectivities and reflectivities significantly below the noise threshold).

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Gerard E. Klazura and Robert G. Pritchard

Abstract

Digital radar data and atmospheric sounding information were analyzed with the intention of beginning a search for atmospheric parameters which are easily attainable, are independent of whether or not clouds are seeded, and either individually or in concert with others can be used to predict the potential size, intensity and coverage of convective precipitation as estimated by radar. Stability indexes and upper level wind speeds seemed to be the dominant predictor variables.

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Gerard E. Klazura and Clement J. Todd

Abstract

A systematic modeling exploration has been conducted to map the growth and trajectory of hygroscopically initiated precipitation particles. The model used is a one-dimensional, steady-state, condensation-coalescence model with adiabatic cloud water content. Drop breakup and freezing were simulated but competition among precipitation particles was not considered. Sizes of initial hygroscopic seeds varied from 5 to 400 μm in diameter, updraft speed ranged from 1 to 25 m s−1, and cloud base temperature varied from 0 to 20°C. The 23 July 1970 salt seeding case reported by Biswas and Dennis was also analyzed using the model.

The numerical simulations reveal several complex interactions: 1) For slow updrafts, the larger hygroscopic seeds travel through a lower trajectory and sweep out less water than small, hygroscopic seeds which are also more apt to grow large enough to break up and create additional large precipitation particles. 2) For fast updrafts, the larger hygroscopic seeds grow into precipitation and stand a better chance of breaking up and initiating a Langmuir chain reaction, while the small hygroscopic particles are carried up to the cirrus level and are lost before they reach precipitation size. 3) For very strong updrafts only large hygroscopic seeds will have a chance to convert to precipitation, and in this situation hail is produced. 4) Hygroscopic seeding produces a greater water yield from warmer based clouds.

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Melvin J. Schroeder and Gerard E. Klazura

Abstract

Digital radar data are being collected as part of the Bureau of Reclamation's High Plains Cooperative Program (HIPLEX). The radars used in this study are sensitive, narrow-beam, 5 cm wavelength systems which record echo data on computer compatible magnetic tape. The antenna scans continuously in a volume mode of 360° in azimuth and 12° in elevation. The time interval for a complete volume scan is approximately 5 min. An overview of the HIPLEX radar operational program and data flow from collection to analysis products is presented.

Computer programs to edit, correct, compress, process and archive the data have been developed and tested. Examples and descriptions of printed, microfiche and magnetic tape output are described. These include composite maximum reflectivity and echo top displays, an equivalent reflectivity file, and a case study summary file which contains location, area, volume, rain and motion information for cells that were identified and tracked. It is shown that the flow of digital radar data has a sufficient amount of human intervention to maintain quality control in an evolving computer environment.

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Gerard E. Klazura and David A. Imy

The NEXRAD program is deploying a network of approximately 160 weather radars throughout the United States and at selected overseas sites. The WSR-88D systems provide highly sensitive, fine-resolution measurements of reflectivity, mean radial velocity, and spectrum width data and generate up to 39 categories of analysis products derived from the base data every five to ten minutes. This paper provides an overview of the analysis products that are available on the WSR-88D systems. Primary uses and limitations of these products are discussed, and several examples are presented. A brief description of the WSR-88D system, including primary components, antenna scanning strategies, and product dissemination plans is also included.

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Gerard E. Klazura, Jessica M. Thomale, D. Scott Kelly, and Paul Jendrowski

Abstract

Radar-estimated rainfall amounts from the NEXRAD Weather Surveillance Radar precipitation accumulation algorithm were compared with measurements from numerous rain gauges (1639 radar versus gauge comparisons). Storm total rain accumulations from 43 rain events from 10 radar sites were analyzed. These rain events were stratified into two precipitation types: 1) high-reflectivity horizontal gradient storms and 2) low-reflectivity horizontal gradient events. Overall, the radar slightly overestimated rainfall accumulations for high-reflectivity gradient cases and significantly underestimated accumulations for low-reflectivity gradient cases. Varying degrees of range effects were observed for these two types of precipitation. For high-reflectivity gradient cases, the radar underestimated rainfall at the nearest ranges, overestimated at the middle ranges, and had fairly close agreements at the farthest ranges. A much stronger range bias was evident for low-reflectivity gradient cases. The radar underestimated rainfall by at least a factor of 2 in the nearest and farthest ranges, and to a somewhat lesser extent at midranges.

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Margaret A. LeMone, Robert L. Grossman, Richard L. Coulter, Marvin L. Wesley, Gerard E. Klazura, Gregory S. PouIos, William Blumen, Julie K. Lundquist, Richard H. Cuenca, Shaun F. Kelly, Edward A. Brandes, Steven P. Oncley, Robert T. McMillen, and Bruce B. Hicks

This paper describes the development of the Cooperative Atmosphere Surface Exchange Study (CASES), its synergism with the development of the Atmosphere Boundary Layer Experiments (ABLE) and related efforts, CASES field programs, some early results, and future plans and opportunities. CASES is a grassroots multidisciplinary effort to study the interaction of the lower atmosphere with the land surface, the subsurface, and vegetation over timescales ranging from nearly instantaneous to years. CASES scientists developed a consensus that observations should be taken in a watershed between 50 and 100 km across; practical considerations led to an approach combining long-term data collection with episodic intensive field campaigns addressing specific objectives that should always include improvement of the design of the long-term instrumentation. In 1997, long-term measurements were initiated in the Walnut River Watershed east of Wichita, Kansas. Argonne National Laboratory started setting up the ABLE array. The first of the long-term hydrological enhancements was installed starting in May by the Hydrologic Science Team of Oregon State University. CASES-97, the first episodic field effort, was held during April–June to study the role of surface processes in the diurnal variation of the boundary layer, to test radar precipitation algorithms, and to define relevant scaling for precipitation and soil properties. The second episodic experiment, CASES-99, was conducted during October 1999, and focused on the stable boundary layer. Enhancements to both the atmospheric and hydrological arrays continue. The data from and information regarding both the long-term and episodic experiments are available on the World Wide Web. Scientists are invited to use the data and to consider the Walnut River Watershed for future field programs.

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