Radar Reflectivity Of Storms Containing Spongy Hail

Author : Pauline Morrow Austin
Publisher :
ISBN 13 :
Total Pages : 35 pages
Book Rating : 4.:/5 (319 download)

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Download or read book Radar Measurements of Severe Storms in New England written by Pauline Morrow Austin and published by . This book was released on 1962 with total page 35 pages. Available in PDF, EPUB and Kindle. Book excerpt: Two investigations concerning severe storms are presented in this report. The basic data for both are iso-echo contours of the averaged, range-corrected signal, photographed from the PPI of a 10-cm radar. These quantitative measurements at a wavelength unaffected by rain attenuation are particularly suitable for the study of severe storms. A numerical investigation of New England squall lines was undertaken for the purpose of providing a quantitative description which can be used for statistical analysis and as a basis for formulating and testing dynamic models. Eight squall lines are analyzed and three charts are plotted for each one: a total intensity chart which shows the rate at which water is being precipitated in the whole line as a function of time; a space composite showing the distribution of rain in a moving grid attached to the squall line; a time-space composite showing the distribution of rain along the line as a function of time. The use of a coordinate system attached to the line permitted investigation of changes in internal structure while eliminating effects produced by the motion of the line as a whole. There were large differences from storm to storm in overall intensity and areal coverage. The time scale was roughly the same for all the lines as were the motions and orientation with respect to the prevailing wind. Strong similarities in internal structure were noted with most of the lines being very narrow and well defined and all of them having persistent groups of intense storms spaced 25-35 miles apart. Two distinct modes of development were observed with four storms in each group. The second investigation is concerned with the reflectivity of hailstorms at a 10-cm wavelength. Comparison is made between occurrence and size of hail and radar reflectivity for a large number of storms on six days in 1961. Over 800 reports of hail occurrences were received on those days. They were reduced to 275 by grouping together those from any single town at approximately the same time and by excluding those which were not observable by the radar because of either location or time of occurrence. On four days when the thunderstorms were in squall lines, 95% of the reported hail occurrences were located in echoes whose equivalent Z values exceeded 105.5 mm6 /m3. Also, on those days, except for a few spots which were very small in area and of short duration, reports of hail were received from all regions where reflectivity factors exceeded 105.5 unless they were located entirely over the ocean or swamp areas. It is clearly shown that, for this type of storm, reflectivity is related to the size of hailstones. In the Boston area if [mathematical equation] the storm contains hail probably 1/4" 6.0 to 1/2" in size. If [mathematical equation] the largest size hailstones are likely to be e 6.5 nearly 1" in diameter; while for [mathematical equation] hailstones the size of golf balls e may be expected. On two days when there were scattered air mass thunderstorms, 80% of the reported hail occurrences were in storms where [mathematical equation]. On these days the storms were generally of brief duration and were small in both horizontal and vertical dimensions. Measured reflectivities were closely related to the ranges of the storms, suggesting that in many cases the radar beam was not adequately filled with intense precipitation.