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  • Author or Editor: John D. Marwitz x
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August H. Auer Jr.
and
John D. Marwitz

Abstract

Based on airborne observations, estimates of air and moisture flux have been calculated for 18 hailstorms: eight in Colorado, one in Oklahoma, and nine in South Dakota. The average air flux for hailstorms in this study was 2.3 × 1011 gm sec−1, while the moisture flux averaged near 2.1 × 109 gm sec−1.

Precipitation efficiency for eight thunderstorms was found to be near 55%, though two severe hailstorms did exhibit slightly less efficiency.

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John D. Marwitz
,
August H. Auer Jr.
, and
Donald L. Veal

Abstract

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Richard A. Schleusenser
,
John D. Marwitz
, and
William L. Cox

Abstract

Haifall data collected from a fixed network in northeastern Colorado during three seasons (1960–62) included the estimated impact energy, duration of hailfall, most common stone size, maximum stone size, and number of stones per square inch. These basic data,X, along with the transformations, lnN, √X, 3X, and 1/X were analyzed by computer methods to determine which parameters could be used in a statistical analysis of hail suppression experiment. The gamma distribution function was fitted to the hailfall data by the method of maximum likelihood. A chi-square goodness of fit test was applied to the data, and one transformation was tested using a sequential analysis technique.

All parameters except impact energy and number of hailstones per square inch were eliminated from the statistical analysis because of bias, non-homogeneity, or sparsity of samples. Transformations which produced the minimum mean coefficient of variation were logarithm of impact energy (InE) and square root of the number of stones per square inch (√N 1 − 6). It was determined that a target-control analysis was not feasible for the analysis of hail suppression experiment. A period of 3 to 5 years is believed necessary to detect changes of 10 to 25 per cent in the hail parameters. The gamma distribution function fitted only the √N 1 − 6 data. From the results it was concluded that a sequential analysis test alone could not adequately evaluate the effectiveness of a hall modification experiment.

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Brenda M. Pobanz
,
John D. Marwitz
, and
Marcia K. Politovich

Abstract

In light of the significant icing hazard large drops pose to general aviation, two conditions have been previously associated with large-drop formation; these being a warm cloud-top temperature and a low droplet concentration. This paper identifies an additional condition associated with the development of large-drop regions. Wind shear is hypothesized as being a necessary but not sufficient condition for the formation of large drops. Wind shear at cloud top may cause turbulence, Kelvin-Helmholtz waves, and thus the inhomogeneous mixing leading to large drops.

This hypothesis was tested in 29 cases where the Wyoming King Air aircraft made a climb or descent through the top of stratiform clouds. The presence of a wind shear layer was defined by the magnitude of the wind shear and the value of the bulk Richardson number across the layer. In 23 of the 29 cases, wind shear was associated with large-drop regions. A χ2 statistical test was applied to the data. The null hypothesis, where wind shear and large drops were considered independent of each other, was rejected to a significance level of 0.01. From this it can be inferred that large drops and wind shear are related. The depth of the shear layer was usually small, less than 150 m. The validity of the condition of low droplet concentration is questioned since several cases of large drops were found in the presence of a high droplet concentration. These cases were marked by strong wind shear.

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