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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
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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