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S. A. Prentice and D. Mackerras

Abstract

Observations of the ratio of cloud to cloud-ground lightning flashes in thunderstorms have been reviewed, and used to obtain empirical relationships between this ratio (z), latitude (λ) and annual thunder-days (T). The 29 observations, covering a latitude range 69°N to 37°S, gave a mean value of z of 3.35. The empirical relationship proposed between z and λ is
zλλλ
From 26 pairs of values of z and T, covering the range 5 to 81 thunderdays per year, the proposed relationship is
zTTT
zT

Information on z for high latitudes is sparse. It is probable that z lies between 1 and 2 for λ > 60° and T < 10.

The existence of a relationship between z and T is attributed to the fact that both are related to latitude. The relationship between z and λ probably depends on the variation of freezing level height with latitude, and a possible relationship between z and freezing level height is examined.

Where both λ and T are known, the proposed estimate of z for λ up to 60° and T up to 84 is
zλTλTλ
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Jeremy S. Grams, Richard L. Thompson, Darren V. Snively, Jayson A. Prentice, Gina M. Hodges, and Larissa J. Reames

Abstract

A sample of 448 significant tornado events was collected, representing a population of 1072 individual tornadoes across the contiguous United States from 2000 to 2008. Classification of convective mode was assessed from radar mosaics for each event with the majority classified as discrete cells compared to quasi-linear convective systems and clusters. These events were further stratified by season and region and compared with a null-tornado database of 911 significant hail and wind events that occurred without nearby tornadoes. These comparisons involved 1) environmental variables that have been used through the past 25–50 yr as part of the approach to tornado forecasting, 2) recent sounding-based parameter evaluations, and 3) convective mode. The results show that composite and kinematic parameters (whether at standard pressure levels or sounding derived), along with convective mode, provide greater discrimination than thermodynamic parameters between significant tornado versus either significant hail or wind events that occurred in the absence of nearby tornadoes.

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G. K. Grice, R. J. Trapp, S. F. Corfidi, R. Davies-Jones, C. C. Buonanno, J. P. Craven, K. K. Droegemeier, C. Duchon, J. V. Houghton, R. A. Prentice, G. Romine, K. Schlachter, and K. K. Wagner
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