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P. Gates
and
H. Tong

Abstract

Using the method of Akaike's Information Criterion (AIC), we present a critical discussion on the determination of the order (i.e., “memory”) of an ergodic Markov chain with a finite number of states. We apply this method to sequences of wet and dry days observed at Manchester and Liverpool, England. We reexamine the Tel Aviv data and argue that a Markov chain of order not lower than 2 should be fitted, instead of the previously fitted first order. We further consider the use of AIC in investigating local stationarity. Finally, the sensitivity of the method when the sample size is reduced is briefly examined. The method proposed in this paper will enable practicing meteorologists to set up an automatic “Markov chain modeler”.

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P. D. Thompson
and
W. Lawrence Gates

Abstract

A two-parameter baroclinic model for vertically integrated flow is derived under the assumption of an isogonal geostrophic wind shear, and constitutes a generalization of the theory of equivalent baroclinic flow. The computational procedures used to apply both this theory and that for purely barotropic flow to the production of numerical forecasts are described in detail, and this is followed by a brief summary of the results of an extensive series of numerical integrations of the equations of both the barotropic and thermotropic models. In all, a total of 120 24-hour forecasts were made every 12 hr from a series of especially prepared maps throughout the entire month of January 1953, the largest collection of numerical forecasts assembled to the present time.

From a preliminary summary of the results supported by the discussion of several individual cases, it appears that the major characteristics of this series of numerical forecasts are: (1) the lack of a significant difference between the barotropic and thermotropic 500-millibar forecasts, the correlation between the predicted and observed 24-hr 500-mb height changes being 0.74 in each case, (2) the marked effects of a number of purely mathematical errors or errors of method, especially those introduced by the lateral boundary conditions and by the use of the finite-difference approximation, and (3) an important effect of the Rocky Mountain barrier on the forecasts. These results are interpreted as demonstrating the quasi-barotropy of the atmosphere at mid-tropospheric levels when considered on a day-to-day basis over a monthly period. The 1000-mb forecasts computed from the baroclinic theory, while displaying an average correlation between predicted and observed 24-hr height changes of only 0.62, show considerable synoptic “skill,” especially over the eastern United States. These forecasts are felt to demonstrate conclusively the applicability of numerical prediction techniques to operational forecasting. Further research on the effects of both the physical and mathematical approximations of the methods of numerical prediction is suggested.

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E. P. Lozowski
,
K. J. Finstad
, and
E. M. Gates

Abstract

No Abstract.

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Karen J. Finstad
,
Edward P. Lozowski
, and
Edward M. Gates

Abstract

The work of Langmuir and Blodgett is widely referenced among researchers in the field of ice accretion who are interested in the impingement characteristics of cloud and spray droplets on circular cylinders. In this paper we check the accuracy of those early calculations by integrating the droplet trajectories on a modern digital computer. We then demonstrate the changes which result when an improved formulation for the drag coefficient is used. Our results verify that the original Langmuir and Blodgett calculations are essentially correct for most practical purposes. Except for inertia parameters between 0.125 and 0.25, the relative differences between their results and our new ones do not exceed 10%. At very low collision efficiencies, however, the relative error is larger, with Langmuir and Blodgett tending to overpredict the collision parameters. Tables of our newly calculated data and fitting functions for the collision parameters are presented. We recommend them for future use because they are more accurate and more convenient to use than their Langmuir and Blodgett equivalents. A discussion of some of the limitations of Langmuir and Blodgett's theory is also given.

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GATE

final international scientific plans

International and Scientific Management Group for GATE
,
Joachim P. Kuettner
,
David E. Parker
,
David R. Rodenhuis
,
Heinrich Hoeber
,
Helmut Kraus
, and
G. Philander
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