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R. H. SIMPSON

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R. H. Simpson

The relation between the slope of tropical low pressure axes and the tendency for such lows to deepen or fill has been studied during investigations carried on separately in the Atlantic and in the Pacific ocean areas. The preliminary conclusions drawn from each of the two studies differ considerably and are reviewed herein. Limitations upon the use of vertical wind shear computations in determining the slope of such pressure axes are discussed. Questions are raised regarding the assumption in such computations that the vertical shear of the observed wind is a good approximation of the shear of the geostrophic components. Illustrations are given of the fallacies of reasoning that may result from such an assumption in connection with tropical cyclones.

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R. H. Simpson
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R. H. Simpson

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R. H. Simpson

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The computation of θE, the pseudo-quivalent potential temperature, ordinarily omits the contribution due to specific heats of water vapor. This may he an acceptable practice for temperate-latitude usages but a questionable one when applied in the tropics where lower layers, rich in moisture, may he several; degrees warmer and the vertical gradient larger when this factor is included.

An inexpensive method of computing θE to include the beat capacities of water substance is presented aid the results compared with those derived from several tephigrams which ignore this contribution.

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R. H. Simpson

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Like most government policies directly affecting the welfare of the nation, the evolution of a coherent national policy on hurricane warnings, public preparedness, and subsequent disaster relief has been event motivated—a product of crisis management. This process began near the turn of this century, first with the Spanish–American War, which placed an urgent requirement for warnings to protect naval vessels from hurricanes, and second following the hurricane disaster at Galveston in 1900, reaching maturity after the Camille disaster in 1969. The latter, for the first time, resulted in a spontaneous effort by both federal and state governments and the university community, particularly by the social scientists, which led to the present hurricane policies.

The result of successive crisis management actions by the government and, after Camille, the broadly based response and analyses by the scientific and engineering communities, led to the evolution of a national policy on hurricanes that identifies and assigns responsibilities and actions required for each phase of a threatening event, from anticipation and preparedness, to relief and recovery from a hurricane disaster.

The plan that evolved is a remarkable example of cooperation between federal, state, and local organizations devoted to the protection of life and property, and recovery from disaster. And it is a tribute to the altruism with which both government and private organizations have collaborated to protect and promote public welfare. Nevertheless, the mechanics of relocating coastal residents from harm’s way in the face of a hurricane emergency remain complex and in some areas uncertain, considering the ever-increasing time required for systematic evacuation.

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R. H. Simpson

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R. H. SIMPSON

Abstract

In convective clouds jet aircraft encounter icing at air temperatures lower than −60° C. It may be reasoned that this results from (1) the melting of frozen droplets due to dynamic or frictional heating in the quasi-potential flow around the air foil; (2) the impact of precipitation consisting of ice spheres with liquid water cores; (3) the possibility that raindrops are carried upward by vertical currents so rapidly that the water temperature remains higher than the spontaneous nucleation temperature (−40° C.) while the air temperature is much lower; or (4) the possibility that the spontaneous nucleation temperature is pressure dependent or otherwise variable. This paper investigates the third of these possibilities and finds that the difference in temperature of liquid water and air at 12 km. can be no more than a few degrees except in the case of very large drops carried through deep layers of cloud by intense steady-state updrafts of the kind associated with hail-producing thunderstorms.

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R. H. Simpson

In August 1951 an unusual airplane reconnaissance of a mature typhoon succeeded in collecting extensive data from the eye and adjacent rain area of the storm. The eye, which was clear except for a low stratocumulus undercast, was circular, 40 miles in diameter, and had a central pressure at the surface of 26.43 inches (895 mb) with a sizable pressure gradient from the center to edge of the eye. Walls of nimbostratus surrounding the eye rose like a huge coliseum to a height of 35,000 feet. Two eye soundings from the surface to 17,000 feet were made, the first at midday, the second in late afternoon. These revealed exceptionally warm temperatures, more than 16° C at 17,000 feet, with lapse rates essentially isothermal from the surface to 10,000 feet. Marked cooling occurred between these two soundings in the layer 7,000–10,000 feet. Horizontally, temperature varied little at 800 feet; at 9,000 feet, however, the eye center was nearly 8 C° warmer, and at 18,000 feet 18 C° warmer than the adjacent rain area. At 9,000 feet, significant temperature gradients were confined primarily to the eye, while at 18,000 feet they were concentrated in the rain area.

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R. H. Simpson

The intertropical convergence zone near Panama is studied in light of meteorograph soundings, winds-aloft, and microanalyses of surface reports. When pronounced this phenomenon consists of a relatively narrow zone of cyclonic wind shear. This is frequently associated with a cold-core trough whose slope in the vertical is of cold-front proportions. Its cloud system is characterized primarily by widespread altostratus with convective activity usually quite variable in amount and intensity. Wavelike perturbations which sometimes appear along this line of convergence are found to be important in connection with cyclogenesis.

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