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  • Wiley  (4)
  • 2010-2014  (4)
  • 1
    Publication Date: 2013-07-09
    Description: This paper provides an intercomparison of the dispersive and diffusive properties of several standard numerical methods applied to the 1D linearized shallow water equations without Coriolis term, including upwind and central finite-volume, spectral finite-volume, discontinuous Galerkin, spectral element, and staggered finite-volume. All methods are studied up to tenth-order accuracy, where possible. A consistent framework is developed which allows for direct intercomparison of the ability of these methods to capture the behavior of linear gravity waves. The Courant-Friedrichs-Lewy (CFL) condition is also computed, which is important for gauging the stability of these methods, and leads to a measure of approximate equal error cost. The goal of this work is threefold: first, to determine the shortest wavelength which can be considered “resolved” for a particular method; second, to determine the effect of increasing the order of accuracy on the ability of a method to capture wave-like motion; third, to determine which numerical methods offer the best treatment of wave-like motion. High-order; dispersion analysis; finite-volume methods; finite-element methods; linear gravity waves; dynamical core
    Print ISSN: 0035-9009
    Electronic ISSN: 1477-870X
    Topics: Geography , Physics
    Published by Wiley
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  • 2
    Publication Date: 2013-07-14
    Description: The spectral element dynamical core has been demonstrated to be an accurate and scalable approach for solving the equations of motion in the atmosphere. However, it is also known that use of the spectral element method for tracer transport is costly and requires substantial parallel communication over a single time step. Consequently, recent efforts have turned to finding alternative transport schemes which maintain the scalability of the spectral element method without its significant cost. This article proposes a conservative semi-Lagrangian approach for tracer transport which uses upstream trajectories to solve the transport equation on the native spectral element grid. This formulation, entitled the Flux-Form Semi-Lagrangian Spectral Element (FF-SLSE) method, is highly accurate compared to many competing schemes, allows for large time steps, and requires fewer parallel communications over the same time interval than the spectral element method. In addition, the approach guarantees local conservation and is easily paired with a filter which can be used to ensure positivity. This article presents the dispersion relation for the 1D FF-SLSE approach and demonstrates stability up to a Courant number of 2.44 with cubic basis. Several standard numerical tests are presented for the method in 2D to verify correctness, accuracy and robustness of the method, including a new test of a divergent flow in Carteisan geometry.
    Print ISSN: 0035-9009
    Electronic ISSN: 1477-870X
    Topics: Geography , Physics
    Published by Wiley
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  • 3
    Publication Date: 2013-08-31
    Description: Idealised studies of key dynamical features of the atmosphere provide insight into the behaviour of atmospheric models. A very important, well understood, aspect of mid-latitude dynamics is baroclinic instability. This can be idealised by perturbing a vertically-sheared basic state in geostrophic and hydrostatic balance. An unstable wave mode then results with exponential growth (due to linear dynamics) in time until, eventually, nonlinear effects dominate and the wave breaks. A new, unified, idealised baroclinic instability test case is proposed. This improves on previous ones in three ways. First, it is suitable for both deep- and shallow-atmosphere models. Second, the constant surface pressure and zero surface geopotential of the basic state makes it particularly well-suited for models employing a pressure- or height-based vertical coordinate. Third, the wave triggering mechanism selectively perturbs the rotational component of the flow: this, together with a vertical tapering, significantly improves dynamic balance.
    Print ISSN: 0035-9009
    Electronic ISSN: 1477-870X
    Topics: Geography , Physics
    Published by Wiley
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  • 4
    Publication Date: 2013-06-22
    Description: Three-dimensional advection tests are required to assess the ability of the transport schemes of dynamical cores to accurately model tracer transport on the sphere. A set of three tracer transport test cases for three-dimensional flow is presented. The tests focus on the physical and numerical issues that are relevant to three-dimensional tracer transport; positivity preservation, inter-tracer correlations, horizontal-vertical coupling, order of accuracy, and the choice of vertical coordinate. The first test is a three-dimensional deformational flow. The second test is a Hadley-like global circulation. The final test is a solid body rotation test in the presence of rapidly varying orography. A variety of assessment metrics, such as error norms, convergence rates and mixing diagnostics are used. The tests are designed for easy implementation within existing and developing dynamical cores and have been a cornerstone of the 2012 Dynamical Core Model Intercomparison Project (DCMIP). Example results are shown using the transport schemes in two dynamical cores; the Community Atmosphere Model finite-volume dynamical core (CAM-FV) and the cubed-sphere finite-volume MCore dynamical core.
    Print ISSN: 0035-9009
    Electronic ISSN: 1477-870X
    Topics: Geography , Physics
    Published by Wiley
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