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Verne H. Leverson

Abstract

On 23–24 September 1983 the vicinity of Prescott, Arizona, experienced a 36 h period of recurrent heavy rains. Measurement obtained from a supplemental precipitation survey of the storm-affected area are used to derive maximum 6 h and total storm (36 h) precipitation patterns. Rainfall depth-area-duration (DAD) data computed from the patterns are compared with three standards of precipitation severity: 1) documented extreme rainstorms in the southwestern United States, 2) precipitation-frequency values and 3) probable maximum precipitation (PMP) estimates. The comparisons show the Prescott storm to be an exceptional event that produced rainfall exceeding 100-yr amounts as well as some categories of PMP.

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Verne H. Leverson, Peter C. Sinclair, and Joseph H. Golden

Abstract

During September 1974 in the Lower Florida Keys, the first successful penetrations of mature waterspouts were accomplished by a specially instrumented research aircraft. Throughout the course of each penetration, the measurement system recorded the temperature, the pressure and the three-dimensional velocity field near and within the visible funnel. Multiple penetrations of both cyclonic and anticyclonic waterspouts in various life-cycle stages were achieved. The results indicate that the waterspout funnel structure exhibits 1) a warm central core region, 2) positive vertical velocities of 5–10 m s−1 outside of the warm core, and 3) tangential velocities and horizontal pressure gradients with characteristics similar to but with magnitudes greater than those of the dust devil. A scale analysis of each term in the governing equations of motion suggests a simplified set of modeling equations. The simple Rankine-combined vortex model with cyclostrophic flow explains approximately 75% of the total measured pressure deficit. This compares favorably with Sinclair's (1966, 1973) earlier results for the dust devil vortex.

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