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  • Author or Editor: C. R. McAllister x
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C. R. McAllister

Abstract

Estimators of conditional probabilities of recurrence of six-eighths or more cloud cover, given a set of unconditional probabilities according to initial times, are presented and tested against a sample of Northern Hemispheric data. The estimators are shown to be highly efficient in the sense that more than 95% of the achieved estimates fall within ±0.02 of observed values of the conditional probabilities. A sensitivity analysis is presented to demonstrate that the methodology and results are essentially independent of particular data source with regard to geographic location, climatic regime, or season of the year insofar as parameter determination and concomitant accuracy of estimation are concerned. Extensions to broader classes of meteorological phenomena are also indicated.

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C. B. Emmanuel
,
B. R. Bean
,
L. G. McAllister
, and
J. R. Pollard

Abstract

Acoustic probing of the lower atmosphere (<150 m) reveals structures that appear similar to those of instability waves produced by wind shear at the stable interface of a temperature inversion. The acoustic sounder was located in the vicinity of a meteorological tower 152 m in height. Profiles of wind velocity and temperature were taken during the acoustic sounder operation. Regions of enhanced thermal stability and wind shear produce strong echoes which the acoustic sounder maps on a height vs time facsimile record. In this paper we limit our discussion of those echo returns that have the characteristic appearance of Helmholtz waves. Richardson numbers calculated from the tower measurements over the layer thickness as determined from the acoustic sounder returns appear to he of the order of ½, while sub-strata embedded within the layer thickness exist where the Richardson number drops near the theoretically predicted critical value of ¼. In addition, measurements of the wavelengths associated with the “breaking” phenomenon conform to the theoretically predicted range of values.

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