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DOUGLAS M. A. JONES

Abstract

The reduction in catch due to the shape of the housing of the U.S. Weather Bureau standard recording gage was explored using data from Weather Bureau stations with both recording and nonrecording gages, a gaging site which included both a standard nonrecording gage and a Stevens recording gage, and gages on the East Central Raingage Network. It was found that, on the average, the standard 8.0-in. diameter orifice recording gage caught 2.5 to 6 percent less rain than the nonrecording gage and 2.5 percent less rain than the recording gage fitted with a 12-in. diameter orifice. The Stevens recording gage caught 5.5 percent less rain than the nonrecording gage. It is concluded that proximity of a sloping portion of the gage housing on the 8-in. diameter orifice recording gages is responsible for the catch reduction.

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Douglas M. A. Jones

Abstract

Volume samples of raindrop spectra (26 865 m3) recorded at ten widely dispersed sites from the tropics to the Aleutian Islands yielded spectra with dominant modes in the range 0.8–1.6 mm. Peaks at the 0.9-mm diameter were found but were not significantly more frequent than other nearby sizes. Secondary peaks in the averaged spectra were detected for some rain-rate and site combinations but not uniformly in all samples.

This study provides an indication of the limits of the extent to which local peaks, resulting from size preferences during drop breakup, could be expected to be seen in data obtained with instruments of limited sample volumes.

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Douglas M. A. Jones

Abstract

An investigation of the physical shape of raindrops using two cameras at right angles is described, and the results are tabulated and graphed. The data included measurements of 1783 raindrops of which 569 were classified as spherical, 496 as oblate, 331 as prolate, and 387 unclassified. The sizes measured ranged up to 6.4 mm equivalent spherical diameter. It is concluded that there is a mean shape which varies uniformly with the mass of the raindrop, but that this shape is the result of oscillation about the mean.

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Douglas M. A. Jones

Abstract

It is shown that the Z-R relationship determined by Cunning and Sax (1977) includes additional useful information of cloud physics. The physical processes by which the tropical rainshafts were formed was simple, probably with a single method of drop formation. Comparable Z-R relationships from the Marshall Islands are given. It is shown that the selection of R as the independent variable usually results in a laser coefficient and a smaller exponent than when Z is taken as the independent variable.

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Douglas M. A. Jones and Wayne M. Wendland

Abstract

Known sources of data from arrays of instantaneous precipitation intensity recorders in southern Germany, east-central Illinois, northeastern Illinois, central Florida, and Hilo, Hawaii are obtained. These data are analyzed for line averages of the percent frequency of occurrence of the exceedance of selected threshold precipitation intensities. The correlation coefficients of the precipitation intensity at sites at varying distances from a reference site are determined. The decay in correlation is found to be a function of climatic region and the type of precipitation: showery or continuous. Showery rains are found to be essentially uncorrelated about 12 km from the reference site while continuous rain exhibits no correlation beyond about 50 km.

Single-station intensity data collected at Urbana, Illinois; Paris, France; Inyanga, Zimbabwe; Bogor, Indonesia; Reading, United Kingdom; Island Beach, New Jersey; Miami, Florida; Franklin, North Carolina; and Majuro, Marshall Islands, are compared.

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DOUGLAS M. A. JONES and FLOYD A. HUFF

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Lawrence A. Dean and Douglas M. A. Jones

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Douglas M. A. Jones and Arthur L. Sims

Abstract

Raingage records from four climatic zones (maritime subtropical, continental temperate, maritime temperate and midlatitude interior) were analyzed to study instantaneous rainfall rates as defined by 1 and 4 min accumulations. The frequency distribution of rainfall rates was determined for stations in each of these climatic zones and a zonal average frequency distribution calculated. A progression in the frequency of more intense precipitation was found from the North Pole to the Equator since all of the data were taken from the Northern Hemisphere. The most intense rainfalls were recorded at stations in the maritime subtropical zones and the least intense rainfalls in the maritime temperate zones.

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Arthur L. Sims and Douglas M. A. Jones

Abstract

Two-minute rainfall rates have been measured along lines of recording rain gages in Florida and Illinois. Knowledge of the frequencies of occurrence of short-duration rainfall rates is needed for estimating attenuation of radio communications and radars. Rainfall rate frequencies are also useful in estimating the erosion of high-speed devices by rain. Results are presented for one summer of data taken at each location. The Florida lines were 9.6 and 21.5 km in length and the Illinois lines 23.9 and 62.2 km. These line frequencies are compared with single gage frequencies at each location. The frequencies by which various rates are exceeded are shown for those that occur more than 0.001% of the time. Rain at rates greater than 0.1 mm h−1 occurred less than 6% of the time at either location and for the longest line lengths. For similar line lengths, most rainfall rates have higher frequencies of occurrence in Florida than in Illinois. The rainfall rate frequencies were not significantly different for differing line orientations.

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Stanley A. Changnon Jr., Douglas M. A. Jones, and Floyd A. Huff

Abstract

The studies described in the companion paper (Part 1) led to an intensive field study in July 1970. The field study employed networks of recording raingages, wind recorders, and hygrothermographs, along with a meteorological radar, cloud cameras, and a meteorologically-instrumented aircraft. The study occurred in an abnormally dry period with mostly air mass showers (non-frontal storm). These air mass showers were found to be enhanced partially by the moisture derived from the forested hills under low wind speed conditions. In addition, the low speed winds from the south were found to be directed by the valleys within the hills, so as to develop a convergent pattern above the hills where the atmosphere was convectively unstable.

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