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HARRIS A. JONES

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HARRIS A. JONES

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DOUGLAS M. A. JONES

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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

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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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D. M. A. Jones

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WALTER A. JONES

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Douglas M. A. Jones

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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

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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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P. A. Jones

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Observations of cloud cover (in oktas or tenths) by ground-based observers have been studied to investigate the distribution of cloud-cover amounts and the correlation of cloud cover in time and space. The correlation between observations at the same station, at different times, was found to vary as an exponential of the time separation. Similarly, the correlation between observations at different stations at the same time was found to vary as an exponential of the distance between the stations. Characteristic scales of cloud variation in space and time were derived from these exponentials and the shape of the distribution (in oktas or tenths) of cloud cover was described by a shape parameter. It was found that the data show only weak correlations between these three derived parameters, although it may be expected from physical arguments that the parameters are related.

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David A. Jones and Ian Simmonds

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This study examines the time-space structure of the standard deviation of daily summer and winter mean sea level pressure over the Southern Hemisphere, as identified in 20 years of analyses generated by the Australian Bureau of Meteorology and two long simulations with a GCM. The unfiltered variability derived from the operational analyses generally display a deal of zonal symmetry, particularly during the summer period, with maxima in the midlatitudes. The percentage of the temporal variance which is explained by the bandpass and low-pass components is calculated; in January and July the percentage of the variance explained by the bandpass data is maximized between 30° and 60°S and assumes values of typically 25%. In general, the low-pass data account for more of the variance and tends to achieve its maxima in low and high latitudes. The greatest contribution to the low-frequency field comes from the planetary-scale waves, particularly at higher latitudes. The synoptic and small-scale waves are generally found to be the dominant contributors to the variance in the higher-frequency bandpass fields, particularly in the region of the hemispheric storm track.

Similar analyses applied to the output of the GCM suggest that, overall, the model performs reasonably well, although the quality of the simulation of the low-frequency variability is inferior to that of the synoptic time scales. The tendency of the model to overpredict the winter daily mean sea level pressure variability in the South Pacific appears to be mostly due to this error in the low-frequency part of the field.

These results reveal a considerable difference between the location of cyclone centers and bandpassed mean sea level pressure variability in the high southern latitudes. The model data imply that the maxima of the bandpassed variability tend to be some 30°–40° of longitude to the west and 5°–7° latitude to the north of those of cyclone centers. This serves to underline the dangers and ambiguity of referring to regions of high variability as “storm tracks.”

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