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James P. Edge and Ferdinand Baer

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Bradley A. Ballish and Ferdinand Baer

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Various normal-mode initialization techniques are applied to a simple 12-level linear model with boundary layer friction, and results are compared to exact solutions of the model. It is found that Machenhauer's initialization scheme gives an approximate solution to the initialization of ageostrophic circulations due to friction; however, all or almost all vertical modes must be initialized and a moderate number of iterations are required. Second-order Baer-Tribbia initialization is found to be less effective than several iterations of the Machenhauer procedure. An iterative initialization based on bounded derivative theory and requiring the second time derivatives of the gravity modes to vanish gives excellent results, but a simple iterative scheme to achieve this diverges with moderate friction. The successful application of these procedures to the initialization of ageostrophic circulations due to friction in numerical weather prediction models will require careful utilization of, and possibly improved, iterative methods to achieve convergence and stability.

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Ferdinand Baer and George W. Platzman

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The vorticity equation may be integrated in spectral form by constructing a table of interaction coefficients. A method is given for computing and ordering this table and for performing the numerical integration. An advantage of the spectral form over the usual grid-point forms is that no mapping of the spherical surface is required. The results are discussed briefly for a 43-day trial integration in one-hour steps.

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Ferdinand Baer, Houjun Wang, Joseph J. Tribbia, and Aimé Fournier

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As an effort toward improving climate model–component performance and accuracy, an atmospheric-component climate model has been developed, entitled the Spectral Element Atmospheric Climate Model and denoted as CAM_SEM. CAM_SEM includes a unique dynamical core coupled at this time to the physics component of the Community Atmosphere Model (CAM) as well as the Community Land Model. This model allows the inclusion of local mesh refinement to seamlessly study imbedded higher-resolution regional climate concurrently with the global climate. Additionally, the numerical structure of the model based on spectral elements allows for application of state-of-the-art computing hardware most effectively and economically to produce the best prediction/simulation results with minimal expenditure of computing resources. The model has been tested under various conditions beginning with the shallow water equations and ending with an Atmospheric Model Intercomparison Project (AMIP)-style run that uses initial conditions and physics comparable to the CAM2 (version 2 of the NCAR CAM climate model) experiments. For uniform resolution, the output of the model compares favorably with the published output from the CAM2 experiments. Further integrations with local mesh refinement included indicate that while greater detail in the prediction of mesh-refined regions—that is, regional climate—is observed, the remaining coarse-grid results are similar to results obtained from a uniform-grid integration of the model with identical conditions. It should be noted that in addition to spectral elements, other efficient schemes have lately been considered, in particular the finite-volume scheme. This scheme has not yet been incorporated into CAM_SEM. The two schemes—finite volume and spectral element—are quasi-independent and generally compatible, dealing with different aspects of the integration process. Their impact can be assessed separately and the omission of the finite-volume process herein will not detract from the evaluation of the results using the spectral-element method alone.

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James P. Lodge, James E. McDonald, and Ferdinand Baer

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Melander's experimental results on the apparent production of salt nuclei by evaporation of salt solutions are examined both theoretically and experimentally. It is concluded theoretically that the rate of evaporative escape of molecular sodium chloride or other salts from sea water is too low by a factor of 1018 to account for the formation of the nuclei active in cloud condensation. It is shown experimentally that the rate of collection of salt particles of diameter in excess of 0.05 micron over evaporating salt solution is too low by a factor of at least 106 to account for the observed rate of atmospheric condensation. Therefore, there appears to be no basis for accepting Wright's suggestion that Melander's work provides an answer to Simpson's long-standing objection to the sea-salt hypothesis of condensation nuclei.

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Lawrence A. Hughes, Ferdinand Baer, Gene E. Birchfield, and Robert E. Kaylor

It is believed that the severity of the storm hitting Canada on October 15, 1954 was due to the addition of an independent development to the dying hurricane Hazel. The problem of forecasting this event is discussed in the light of forecasts made at the time. The presence of a secondary development is verified.

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Houjun Wang, Joseph J. Tribbia, Ferdinand Baer, Aimé Fournier, and Mark A. Taylor

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The authors describe a recent development and some applications of a spectral element dynamical core. The improvements and development include the following: (i) the code was converted from FORTRAN 77 to FORTRAN 90; (ii) the dynamical core was extended to the generalized terrain-following, or hybrid η, vertical coordinates; (iii) a fourth-order Runge–Kutta (RK4) method for time integration was implemented; (iv) moisture effects were added in the dynamical system and a semi-Lagrangian method for moisture transport was implemented; and (v) the improved dynamical core was coupled with the Community Atmosphere Model version 2 (CAM2) physical parameterizations and Community Land Model version 2 (CLM2) in such a way that it can be used as an alternative dynamical core in CAM2. This spectral element version of CAM2 is denoted as CAM-SEM. A mass fixer as used in the Eulerian version of CAM2 (CAM-EUL) is also implemented in CAM-SEM. Results from multiyear simulations with CAM-SEM (coupled with CLM2) with climatology SST are also presented and compared with simulations from CAM-EUL. Close resemblances are shown in simulations from CAM-SEM and CAM-EUL. The authors found that contrary to what is suggested by some other studies, the high-order Lagrangian interpolation (with a limiter) using the spectral element basis functions may not be suitable for moisture and other strongly varying fields such as cloud and precipitation.

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