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Phillip J. Smith

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Phillip J. Smith

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A procedure is introduced which allows estimation of the net influence of subgrid-scale thermodynamic processes on large-scale available potential energy. A numerical example representing the average energetics over North America for March, 1962 suggests that “net” subgrid-scale generation greatly exceeds the average grid-scale generation, with positive contributions occurring in the low and middle troposphere.

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Phillip J. Smith

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Diagnostic and modeling results reveal that atmospheric heating typically acts to intensify extratropical cyclones. In addition, both the Petterssen–Sutcliffe and Zwack–Okossi development equations reveal that this relationship depends on the proportionality that exists between surface geostrophic vorticity tendency and the negative of the horizontal Laplacian of atmospheric heating. Because of this Laplacian relationship, the impact of a heating field with a given magnitude and vertical distribution depends on its horizontal distribution. This paper will show how horizontal heating distributions that differ by relatively small amounts over their entire extent can yield vorticity tendency responses that could contribute to either development or decay of an underlying cyclone.

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PHILLIP J. SMITH

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Several techniques exist for computing vertical motions. In this paper, radiosonde wind observations are used to compute vertical motions by the kinematic method. The presence of cumulative bias errors necessitates adjustment techniques. Simple tests of two techniques indicate that, for the period of this study, a divergence adjustment that is a function of pressure yields the best adjusted vertical motion fields. Further analysis shows that the adjusted estimates correlate well with observed synoptic features. Finally, comparison with estimates by the numerical method indicates that adjusted kinematic vertical motion fields are comparable.

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PHILLIP J. SMITH

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The kinetic energy budgets of several examples of synoptic scale systems are reviewed. Included are systems containing a major cyclone development, the immediate cyclone vicinity, and the anticyclone preceding the cyclone development. These are then considered in terms of their role in the general circulation of the middle latitudes.

Results show that the cyclone system and cyclone vicinity are respectively about two and five times more active energetically than the general circulation. Further, when averaged with results of Petterssen and Smehye, the resulting mean cyclone system accounts for about one-third of the energetic activity of the middle latitudes. On the other hand, circulations associated with the anticyclone case exhibit much less intense energetic properties.

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Phillip J. Smith and John T. Snow
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James M. Vasilj and Phillip J. Smith

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This note compares the extended (EXT) and quasigeostrophic (QG) dynamics of a small–Rossby number extratropical cyclone using the Zwack–Okossi (ZO) equation. Applied to a cyclone that occurred on 8–9 November 1985 over the North Atlantic Ocean, results show that although differences exist, both the EXT and QG forms of the ZO equation provide very adequate estimates of the large-scale forcing processes associated with this case.

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Yi-Tsuei Pai Sheu and Phillip J. Smith

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A diagnostic analysis of kinetic energy budgets for midlatitude 500 mb synoptic-scale waves in the winter–spring season is presented. The data used were standard twice-daily rawinsonde observations in 50 mb increments from the surface to 100 mb over Southern Canada and the United States for December 1967, 1969 and March, April 1970. The computed kinetic energy budgets were stratified into groups according to the wave number domain, trough/ridge orientation, stage of intensification, and intensity level and were partitioned into barotropic and baroclinic components. The latter was accomplished by separating the total kinetic energy budget equation into its vertical mean and shear parts.

Several conclusions can be drawn from the results of this study. 1) Kinetic energy generation and dissipation balance each other in the boundary layer for all stratifications. 2) Although not balanced, a significant negative correspondence between the generation and the horizontal transport exists in the, free atmosphere. Positive generation and horizontal flux divergence are observed in most waves. 3) In contrast to previous studies, a weak subgrid- to grid-scale exchange of kinetic energy occurs in the upper troposphere. This may be the result of excluding strongly interacting wave cases and longer wave-length flows in the present study. 4) The barotropic component of the flow is 2–2.5 times larger than the baroclinic. 5) Both barotropic and baroclinic processes provide a source of kinetic energy to the wave cases. Most of the baroclinic source is contributed below 700 mb, with baroclinic processes extracting kinetic energy above that level. 6) Kinetic energy dissipation occurs primarily in the barotropic flow component. In the baroclinic component, subgrid- to grid-scale energy exchange is present. 7) The kinetic energy is converted from the vertical shear to mean flow, indicating that in these wave cases the atmosphere tends toward a more barotropic state at the expense of the baroclinic state.

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Randy A. Peppier and Phillip J. Smith

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Comparisons are made between second-order and fourth-order finite differencing using three grid resolutions in order to analyze the truncation errors in geostrophic wind and relative vorticity estimates. Horizontal wave dimensions are also varied to study sensitivity to different scales of motion. Exact calculations derived from analytic equations describing geostrophic wind and relative vorticity provide the standard against which the finite-difference estimates are compared.

Both wind speed and relative vorticity truncation errors maximized in regions where speed and vorticity values were greatest. These errors were, in general, smaller for longer wavelengths, finer grid resolution and fourth-order differencing. Although second-order differencing produced fields that were numerically less than observed and yielded errors which decreased with reduced grid interval, fourth-order differencing departed from this anticipated behavior. Rather, when the grid interval was reduced to the point that the wavelength was ten times or more greater than the grid interval, wind speeds and vorticities estimated by the fourth-order scheme were overestimated and were accompanied by increased truncation errors at finer grids.

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Shiang-Jiun Lin and Phillip J. Smith

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A simple scheme for utilizing satellite Cloud Pattern information to improve the estimation of parameterized stable and convective latent heat release is proposed and tested for an extratropical cyclone occurring over the United States during 9–11 January 1975. Calculations are done over the standard North American rawinsonde data region and over a sparse data region simulated by ignoring one-third of the original rawinsonde stations. Results indicate a 15% and 30% improvement in latent heating estimates derived from the total and sparse datasets, respectively. A larger improvement was found using the sparse dataset because the parameterized latent heat release estimates obtained using these data were poorer than those obtained using the total dataset.

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