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Robert D. Fletcher
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Robert D. Fletcher

A meteorological analysis is made of the general rainstorm of June 9–12, 1945, which produced substantial streamflow measurements over the Rio Tuy drainage basin of Venezuela. In this storm it appears that the intertropical convergence zone (ITC), in combination with the orography of the basin, was the weather model responsible for the rain.

There is shown to be a high correlation (a coefficient of 0.73) between the mean-annual-rainfall pattern and that of the June 9–12 storm. The same correlation coefficient is found between the mean-annual pattern and that of another storm which occurred between June 28 and July 2, 1945. It is concluded that most general rainstorms over the Rio Tuy Basin occur when the ITC, oriented such that the trade winds are blowing almost directly from the east, lies just south of the basin; that the isohyetal patterns which result are very much alike; and that the magnitude of the rainfall varies with the strength of the trade-wind current flowing over the basin.

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Robert D. Fletcher
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Robert D. Fletcher
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Robert D. Fletcher
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Robert D. Fletcher

Abstract

Recent experiences with tropical meteorology around the world have brought to light the frequent existence of a zonal band of west winds in the vicinity of the equator, which appears not to be associated with the westerlies of middle latitudes, but which rather seems to be found between the trades of the two hemispheres. The boundaries of the equatorial westerlies are usually characterized by increased cloudiness and poor weather. In this paper an attempt is made to prove that the westerlies of equatorial regions are not simply transitory phenomena but instead should be considered as an integral part of the normal general circulation of the atmosphere. Seasonal variation of the latitude of maximum insolation is the factor introduced to explain the existence of the west winds. A second explanatory theory is discussed in which radiation from the cloud tops of the “intertropical convergence zone” locally reverses the equatorial solenoidal field to produce two new lines of convergence, one on each side of the equator. The same theory is the basis for a discussion of the rather complex structure of the intertropical convergence zones in each of which multiple lines of cloud build-ups are frequently observed. The paper also points out that the polar front is not to be identified with the high latitude zone of low pressure that appears in general circulation schemes, but rather that the front lies well equatorward from the low pressure zone as a result of topographical irregularities which, in turn, cause traveling disturbances, the low pressure centers of which fall well within the cold air on the poleward side of the statistical latitude of the polar front.

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Robert D. Fletcher
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Robert D. Fletcher

It is brought out that axes of strong-wind currents have preferences for particular contour heights on upper-air constant-pressure surfaces. The tendency for coincidence of contour lines and strong-wind axes is emphasized as an aid in upper-wind forecasting. A climatological study also demonstrates a consistent average relation between wind speed, contour height, and latitude.

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Robert D. Fletcher and Kenneth A. Rice
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Robert D. Fletcher and Nicholas E. Manos

Relationships between smoke concentration and visibility, wind direction, wind speed, and temperature stratification are discussed with some references to previous investigations which have related these factors. The paper deals with smoke pollution such as exists in an industrial city, rather than with the effluent from a point- or line-source drifting over an area of constant surface roughness. The review includes some of the findings of the writers, who have made a number of correlations between Weather Bureau meteorological data and Davidson's New York City smoke data of 1939–40. The best of these correlations resulted when the wind direction and wind speed were considered hour by hour for each day, and when a straight-line regression formula was fitted to the data. It is brought out that isobaric curvature, as shown on the weather maps, seems to be a significant factor in the smoke-spreading problem.

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