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  • 1
    Online Resource
    Online Resource
    Wiley ; 2006
    In:  Quarterly Journal of the Royal Meteorological Society Vol. 132, No. 621C ( 2006-10), p. 2943-2975
    In: Quarterly Journal of the Royal Meteorological Society, Wiley, Vol. 132, No. 621C ( 2006-10), p. 2943-2975
    Abstract: A deterministic initial‐value test case for dry dynamical cores of atmospheric general‐circulation models is presented that assesses the evolution of an idealized baroclinic wave in the northern hemisphere. The initial zonal state is quasi‐realistic and completely defined by analytic expressions which are a steady‐state solution of the adiabatic inviscid primitive equations with pressure‐based vertical coordinates. A two‐component test strategy first evaluates the ability of the discrete approximations to maintain the steady‐state solution. Then an overlaid perturbation is introduced which triggers the growth of a baroclinic disturbance over the course of several days. The test is applied to four very different dynamical cores at varying horizontal and vertical resolutions. In particular, the NASA/NCAR Finite Volume dynamics package, the National Center for Atmospheric Research spectral transform Eulerian and the semi‐Lagrangian dynamical cores of the Community Atmosphere Model CAM3 are evaluated. In addition, the icosahedral finite‐difference model GME of the German Weather Service is tested. These hydrostatic dynamical cores represent a broad range of numerical approaches and, at very high resolutions, provide independent reference solutions. The paper discusses the convergence‐with‐resolution characteristics of the schemes and evaluates the uncertainty of the high‐resolution reference solutions. Copyright © 2006 Royal Meteorological Society
    Type of Medium: Online Resource
    ISSN: 0035-9009 , 1477-870X
    RVK:
    RVK:
    Language: English
    Publisher: Wiley
    Publication Date: 2006
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    detail.hit.zdb_id: 2089168-4
    SSG: 14
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  • 2
    Online Resource
    Online Resource
    Wiley ; 2014
    In:  Quarterly Journal of the Royal Meteorological Society Vol. 140, No. 682 ( 2014-07), p. 1590-1602
    In: Quarterly Journal of the Royal Meteorological Society, Wiley, Vol. 140, No. 682 ( 2014-07), p. 1590-1602
    Abstract: Idealised studies of key dynamical features of the atmosphere provide insight into the behaviour of atmospheric models. A very important, well understood, aspect of midlatitude 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.
    Type of Medium: Online Resource
    ISSN: 0035-9009 , 1477-870X
    URL: Issue
    RVK:
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    Language: English
    Publisher: Wiley
    Publication Date: 2014
    detail.hit.zdb_id: 3142-2
    detail.hit.zdb_id: 2089168-4
    SSG: 14
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  • 3
    Online Resource
    Online Resource
    American Meteorological Society ; 2012
    In:  Monthly Weather Review Vol. 140, No. 4 ( 2012-04), p. 1257-1284
    In: Monthly Weather Review, American Meteorological Society, Vol. 140, No. 4 ( 2012-04), p. 1257-1284
    Abstract: This paper presents a new approach for discretizing the nonhydrostatic Euler equations in Cartesian geometry using an operator-split time-stepping strategy and unstaggered upwind finite-volume model formulation. Following the method of lines, a spatial discretization of the governing equations leads to a set of coupled nonlinear ordinary differential equations. In general, explicit time-stepping methods cannot be applied directly to these equations because the large aspect ratio between the horizontal and vertical grid spacing leads to a stringent restriction on the time step to maintain numerical stability. Instead, an A-stable linearly implicit Rosenbrock method for evolving the vertical components of the equations coupled to a traditional explicit Runge–Kutta formula in the horizontal is proposed. Up to third-order temporal accuracy is achieved by carefully interleaving the explicit and linearly implicit steps. The time step for the resulting Runge–Kutta–Rosenbrock–type semi-implicit method is then restricted only by the grid spacing and wave speed in the horizontal. The high-order finite-volume model is tested against a series of atmospheric flow problems to verify accuracy and consistency. The results of these tests reveal that this method is accurate, stable, and applicable to a wide range of atmospheric flows and scales.
    Type of Medium: Online Resource
    ISSN: 0027-0644 , 1520-0493
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    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2012
    detail.hit.zdb_id: 2033056-X
    detail.hit.zdb_id: 202616-8
    SSG: 14
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  • 4
    In: WIREs Water, Wiley, Vol. 9, No. 4 ( 2022-07)
    Type of Medium: Online Resource
    ISSN: 2049-1948 , 2049-1948
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2022
    detail.hit.zdb_id: 2751191-1
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  • 5
    Online Resource
    Online Resource
    American Geophysical Union (AGU) ; 2022
    In:  Journal of Geophysical Research: Atmospheres Vol. 127, No. 24 ( 2022-12-27)
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 127, No. 24 ( 2022-12-27)
    Abstract: Global forecasting models struggle to realistically represent negative potential vorticity (PV) arising from mesoscale convective systems Anticyclonic circulation errors associated with negative PV introduce rotational wind errors into the jet stream Jet stream errors associated with negative PV modify the phasing and forecast skill of a Rossby‐wave packet
    Type of Medium: Online Resource
    ISSN: 2169-897X , 2169-8996
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2022
    detail.hit.zdb_id: 710256-2
    detail.hit.zdb_id: 2016800-7
    detail.hit.zdb_id: 2969341-X
    SSG: 16,13
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  • 6
    In: Bulletin of the American Meteorological Society, American Meteorological Society, Vol. 96, No. 9 ( 2015-09), p. 1440-
    Type of Medium: Online Resource
    ISSN: 0003-0007 , 1520-0477
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2015
    detail.hit.zdb_id: 2029396-3
    detail.hit.zdb_id: 419957-1
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  • 7
    In: Bulletin of the American Meteorological Society, American Meteorological Society, Vol. 96, No. 6 ( 2015-06-01), p. 997-1017
    Abstract: While a quantitative climate theory of tropical cyclone formation remains elusive, considerable progress has been made recently in our ability to simulate tropical cyclone climatologies and to understand the relationship between climate and tropical cyclone formation. Climate models are now able to simulate a realistic rate of global tropical cyclone formation, although simulation of the Atlantic tropical cyclone climatology remains challenging unless horizontal resolutions finer than 50 km are employed. This article summarizes published research from the idealized experiments of the Hurricane Working Group of U.S. Climate and Ocean: Variability, Predictability and Change (CLIVAR). This work, combined with results from other model simulations, has strengthened relationships between tropical cyclone formation rates and climate variables such as midtropospheric vertical velocity, with decreased climatological vertical velocities leading to decreased tropical cyclone formation. Systematic differences are shown between experiments in which only sea surface temperature is increased compared with experiments where only atmospheric carbon dioxide is increased. Experiments where only carbon dioxide is increased are more likely to demonstrate a decrease in tropical cyclone numbers, similar to the decreases simulated by many climate models for a future, warmer climate. Experiments where the two effects are combined also show decreases in numbers, but these tend to be less for models that demonstrate a strong tropical cyclone response to increased sea surface temperatures. Further experiments are proposed that may improve our understanding of the relationship between climate and tropical cyclone formation, including experiments with two-way interaction between the ocean and the atmosphere and variations in atmospheric aerosols.
    Type of Medium: Online Resource
    ISSN: 0003-0007 , 1520-0477
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2015
    detail.hit.zdb_id: 2029396-3
    detail.hit.zdb_id: 419957-1
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  • 8
    Online Resource
    Online Resource
    American Meteorological Society ; 2014
    In:  Monthly Weather Review Vol. 142, No. 3 ( 2014-03-01), p. 1221-1239
    In: Monthly Weather Review, American Meteorological Society, Vol. 142, No. 3 ( 2014-03-01), p. 1221-1239
    Abstract: A statically nested, variable-mesh option has recently been introduced into the Community Atmosphere Model’s (CAM's) Spectral Element (SE) dynamical core that has become the default in CAM version 5.3. This paper presents a series of tests of increasing complexity that highlight the use of variable-resolution grids in CAM-SE to improve tropical cyclone representation by dynamically resolving storms without requiring the computational demand of a global high-resolution grid. As a simplified initial test, a dry vortex is advected through grid transition regions in variable-resolution meshes on an irrotational planet with the CAM subgrid parameterization package turned off. Vortex structure and intensity is only affected by grid resolution and no spurious artifacts are observed. CAM-SE model simulations using an idealized tropical cyclone test case on an aquaplanet show no numerical distortion or wave reflection when the cyclone interacts with an abrupt transition region. Using the same test case, the authors demonstrate that a regionally refined mesh with significantly fewer degrees of freedom can produce the same local results as a globally uniform grid. Additionally, the authors discuss a more complex aquaplanet experiment with meridionally varying sea surface temperatures that reproduces a quasi-realistic global climate. Tropical cyclogenesis is facilitated without the need for vortex bogusing in a high-resolution patch embedded within a global grid that is otherwise too coarse to resolve realistic tropical cyclones in CAM.
    Type of Medium: Online Resource
    ISSN: 0027-0644 , 1520-0493
    RVK:
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2014
    detail.hit.zdb_id: 2033056-X
    detail.hit.zdb_id: 202616-8
    SSG: 14
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  • 9
    In: Monthly Weather Review, American Meteorological Society, Vol. 146, No. 11 ( 2018-11-01), p. 3505-3544
    Abstract: Numerical weather, climate, or Earth system models involve the coupling of components. At a broad level, these components can be classified as the resolved fluid dynamics, unresolved fluid dynamical aspects (i.e., those represented by physical parameterizations such as subgrid-scale mixing), and nonfluid dynamical aspects such as radiation and microphysical processes. Typically, each component is developed, at least initially, independently. Once development is mature, the components are coupled to deliver a model of the required complexity. The implementation of the coupling can have a significant impact on the model. As the error associated with each component decreases, the errors introduced by the coupling will eventually dominate. Hence, any improvement in one of the components is unlikely to improve the performance of the overall system. The challenges associated with combining the components to create a coherent model are here termed physics–dynamics coupling. The issue goes beyond the coupling between the parameterizations and the resolved fluid dynamics. This paper highlights recent progress and some of the current challenges. It focuses on three objectives: to illustrate the phenomenology of the coupling problem with references to examples in the literature, to show how the problem can be analyzed, and to create awareness of the issue across the disciplines and specializations. The topics addressed are different ways of advancing full models in time, approaches to understanding the role of the coupling and evaluation of approaches, coupling ocean and atmosphere models, thermodynamic compatibility between model components, and emerging issues such as those that arise as model resolutions increase and/or models use variable resolutions.
    Type of Medium: Online Resource
    ISSN: 0027-0644 , 1520-0493
    RVK:
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2018
    detail.hit.zdb_id: 2033056-X
    detail.hit.zdb_id: 202616-8
    SSG: 14
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  • 10
    Online Resource
    Online Resource
    American Meteorological Society ; 2016
    In:  Journal of the Atmospheric Sciences Vol. 73, No. 9 ( 2016-09-01), p. 3397-3421
    In: Journal of the Atmospheric Sciences, American Meteorological Society, Vol. 73, No. 9 ( 2016-09-01), p. 3397-3421
    Abstract: The paper demonstrates that sudden stratospheric warmings (SSWs) can be simulated in an ensemble of dry dynamical cores that miss the typical SSW forcing mechanisms like moist processes, land–sea contrasts, or topography. These idealized general circulation model (GCM) simulations are driven by a simple Held–Suarez–Williamson (HSW) temperature relaxation and low-level Rayleigh friction. In particular, the four dynamical cores of NCAR’s Community Atmosphere Model, version 5 (CAM5), are used, which are the semi-Lagrangian (SLD) and Eulerian (EUL) spectral-transform models and the finite-volume (FV) and the spectral element (SE) models. Three research themes are discussed. First, it is shown that SSW events in such idealized simulations have very realistic flow characteristics that are analyzed via the SLD model. A single vortex-split event is highlighted that is driven by wavenumber-1 and -2 wave–mean flow interactions. Second, the SLD simulations are compared to the EUL, FV, and SE dynamical cores, which sheds light on the impact of the numerical schemes on the circulation. Only SLD produces major SSWs, while others only exhibit minor stratospheric warmings. These differences are caused by SLD’s more vigorous wave–mean flow interactions in addition to a warm pole bias, which leads to relatively weak polar jets in SLD. Third, it is shown that tropical quasi-biennial oscillation (QBO)–like oscillations and SSWs can coexist in such idealized HSW simulations. They are present in the SLD dynamical core that is used to analyze the QBO–SSW interactions via a transformed Eulerian-mean (TEM) analysis. The TEM results provide support for the Holton–Tan effect.
    Type of Medium: Online Resource
    ISSN: 0022-4928 , 1520-0469
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    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2016
    detail.hit.zdb_id: 218351-1
    detail.hit.zdb_id: 2025890-2
    SSG: 16,13
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