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HARRY R. GLAHN

Abstract

The regression screening and principal component techniques for developing forecast aids are investigated for their applicability to the objective forecasting of rainfall probabilities. The forecasting of summer rainfall in the Mississippi Delta is the particular problem studied. Subjective forecasts made for the area as well as objective forecasts are verified in terms of reductions of variance and saving over climatology. It is found that many of the forecast equations developed by regression screening and principal component techniques are not stable on test data. The results indicate that subjective screening of predictors is desirable before the regression screening is accomplished. It is found that useful aids can be developed with these linear techniques; at the same time the desirability of an approach that better integrates the physical processes of the atmosphere is indicated.

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Harry R. Glahn

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Harry R. Glahn

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Harry R. Glahn

Abstract

The assumptions inherent in the determination of cloud top heights and areal coverage of clouds from infrared measurements made by satellites are discussed. The problems of interpretation caused by radiometer spatial resolution being of the same order of size as individual cloud elements are studied through mathematical simulation of the viewing process. An analysis of the simulated measurements from simple, specified cloud conditions produces quantitative estimates of the errors of interpretation.

It is found that individual cloud elements of a diameter slightly less than the viewed spot can be very misleading and the height of cloud tops might be judged to be several thousand feet below their true height; tops of larger clouds can be determined more accurately. If the actual height of the tops can be determined, either by the infrared measurements from large cloud masses or by other means, the areal coverage can be estimated rather well.

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Harry R. Glahn

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There is a popular misconception that the secant form of the Lambert conformal map projection is “better” than the tangent form. It is shown here that the two forms are equivalent; they are different only in the sense that the scale of the map quoted is usually true at the two secant latitudes for the secant projections and at the single tangent latitude for the tangent projection.

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Harry R. Glahn

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Truncation errors of four stencils for evaluating the two-dimensional Laplacian operator are discussed, and response functions are computed. The efficiencies of the stencils, in terms of number of iterations and computer time required, for solving Poisson's equation by relaxation is investigated. The dependence on the relaxation coefficient of the number of iterations required and the error of the solution is shown for a number of examples.

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THE USE OF DECISION THEORY IN METEOROLOGY

With an Application to Aviation Weather

HARRY R. GLAHN

Abstract

The concepts of decision theory are discussed, especially in the light of their application to meteorology. The use of the principles of decision-making under risk requires certain probability information to be available. The issuance of forecasts in probability terms has a firm basis in theory and has been shown to work well in practice. The best verification statistic of these forecasts is their usefulness to the user and this can be measured and compared with some standard if the utility matrix is known.

A multi-dimensional contingency table technique is used to estimate the conditional probability distribution of the 5-hr. projection of ceiling height at Washington National Airport. Three predictors are screened from 164 possible predictors according to the utility criterion. Developmental and test data results are presented.

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Harry R. Glahn

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Harry R. Glahn

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Harry R. Glahn

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