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Clifford H. Dey

Abstract

A large proportion of the noise in the National Meteorological Center 8-layer global model is due to a high-frequency external and a low-frequency internal gravity-inertia wave mode. Divergence diffusion effectively controls these two noise components, but it has undesirable side effects when used in this global model. However, divergence diffusion can be used to essentially damp either the external or the internal gravity-inertia wave mode individually. Damping the former controls the noise as well as a frequently used time filter, but has an unacceptable side effect in the vicinity of mountains. Damping the latter provides better noise control than the time filter and has no undesirable side effects.

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Clifford H. Dey

Abstract

The application of a simple variation of the Euler-backward integration method to dynamic initialization is discussed. The variation involves few additional computations, is easily programmed and permits the rate of damping to be selected. The technique can be substantially more strongly damping than the Euler-backward method, but at the expense of a reduced time step. The efficiency of the variation when used in dynamic initialization is confirmed by a numerical experiment.

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Clifford H. Dey

Abstract

The objective analysis of meteorological variables has been routinely performed at the National Meteorological Center (NMC) since October 1955. In the first few years, much attention was devoted to incorporating three principles of subjective meteorological analysis into the automated procedures: spatial coherence, temporal continuity, and adherence to dynamic constraints. Consideration of these principles has continued in subsequent years as objective analysis methodology has evolved. That evolution has been driven by three interrelated developments: advances in observing technology, progress in prediction modeling, and a marked increase in computer capability. In light of these factors, this paper surveys the evolution of analysis methodology at NMC from 1955 to the end of 1988.

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CLIFFORD H. DEY

Abstract

Kurihara and Holloway's approach of applying the box integration method to the Kurihara grid has been followed for a global forecast model. After encountering problems with the original system, it was found that the truncation error associated with both the orientation of grid points around each Pole and the computation scheme must be carefully considered. A slight alteration was made in Kurihara's grid which alleviated the troubles and provided acceptable forecasts.

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Clifford H. Dey and Lauren L. Morone

Abstract

A number of changes were made to the National Meteorological Center global data assimilation system (GDAS) during 1982 and 1983. The most significant of these changes was the replacement of the quasi-univariate, sigma-coordinate optimum interpolation analysis procedure by a version that performs a fully multivariate analysis on mandatory pressure surfaces. The new analysis technique is described in some detail. The impact of this and other changes made during 1982 and 1983 on the performance of the GDAS is evaluated.

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Charles P. Arnold Jr. and Clifford H. Dey

A summary of the history of observing-systems simulation experiments (OSSEs) is presented together with a description of current methodology, its capabilities and limitations, and considerations for the design of future experiments. These experiments are defined as a type of sensitivity study and are contrasted with real-data experiments otherwise known as observing-systems experiments (OSEs), data-impact, or data-denial experiments, which form a related type of sensitivity study. Simulation is presented as a means by which an a priori evaluation of proposed remote-sensing systems can be made.

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