Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session H20: DFD/GPC Minisymposium: Global Climate Models: Dynamical Cores, Strengths and Weaknesses |
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Chair: Jim Brasseur, Pennsylvania State University; Brad Marston, Brown University, John Wettlaufer, Oxford University and Yale University Room: 315 |
Monday, November 25, 2013 10:30AM - 10:56AM |
H20.00001: The spectral element dynamical core in the Community Atmosphere Model Invited Speaker: Mark Taylor I will describe our work developing CAM-SE, a highly scalable version of the Community Atmosphere Model (CAM). CAM-SE solves the hydrostatic equations with a spectral element horizontal descritization and the hybrid coordinate Simmons {\&} Burridge (1981) vertical discretization. It uses a mimetic formulation of spectral elements which preserves the adjoint and annihilator properties of the divergence, gradient and curl operations. These mimetic properties result in local conservation (to machine precision) of mass, tracer mass and (2D) potential vorticity, and semi-discrete conservation (exact with exact time-discretization) of total energy. Hyper-viscsoity is used for all numerical dissipation. The spectral element method naturally supports unstructured/variable resolution grids. We are using this capability to perform simulations with 1/8 degree resolution over the central U.S., transitioning to 1 degree over most of the globe. This is a numerically efficient way to study the resolution sensitivity of CAM's many subgrid parameterizations. [Preview Abstract] |
Monday, November 25, 2013 10:56AM - 11:22AM |
H20.00002: A 3-D Finite-Volume Non-hydrostatic Icosahedral Model (NIM) Invited Speaker: Jin Lee The Nonhydrostatic Icosahedral Model (NIM) formulates the latest numerical innovation of the three-dimensional finite-volume control volume on the quasi-uniform icosahedral grid suitable for ultra-high resolution simulations. NIM's modeling goal is to improve numerical accuracy for weather and climate simulations as well as to utilize the state-of-art computing architecture such as massive parallel CPUs and GPUs to deliver routine high-resolution forecasts in timely manner. NIM uses innovations in model formulation similar to its hydrostatic version of the Flow-following Icosahedral Model (FIM) developed by Earth System Research Laboratory (ESRL) which has been tested and accepted for future use by the National Weather Service as part of their operational global prediction ensemble. Innovations from the FIM used in the NIM include: * A local coordinate system remapped spherical surface to plane for numerical accuracy (Lee and MacDonald, 2009), * Grid points in a table-driven horizontal loop that allow any horizontal point sequence (A.E. MacDonald, et al., 2010), * Flux-Corrected Transport formulated on finite-volume operators to maintain conservative positive definite transport (J.-L, Lee, ET. Al., 2010), * All differentials evaluated as finite-volume integrals around the cells, *Icosahedral grid optimization (Wang and Lee, 2011) NIM extends the two-dimensional finite-volume operators used in FIM into the three-dimensional finite-volume solvers designed to improve pressure gradient calculation and orographic precipitation over complex terrain. The NIM dynamical core has been successfully verified with various non-hydrostatic benchmark test cases such as warm bubble, density current, internal gravity wave, and mountain waves. Physical parameterizations have been incorporated into the NIM dynamic core and successfully tested with multimonth aqua-planet simulations. Recent results from NIM simulations will be presented at the Symposium. [Preview Abstract] |
Monday, November 25, 2013 11:22AM - 11:48AM |
H20.00003: Dynamical cores and climate modeling Invited Speaker: Peter Hjort Lauritzen In this talk an overview of the development of next generation dynamical cores in climate modeling is given. Fluid flow solvers intended for coupled climate system models must be designed to respect important physical properties related to conservation and the physical realizability of the computed solution. Demands for increased complexity and higher resolution has forced the modeling community to go back to the drawing board and develop highly scalable solvers on non-traditional spherical grids. In this talk an overview of these topics will be given with specific examples from NCAR's (National Center for Atmospheric Research) Community Atmosphere Model (CAM). [Preview Abstract] |
Monday, November 25, 2013 11:48AM - 12:14PM |
H20.00004: Intercomparison of General Circulation Models for Hot Extrasolar Planet Atmospheres Invited Speaker: James Cho In this collaborative work with I.\ Polichtchouk, C.\ Watkins, H.\ Th.\ Thrastarson, O.\ M.\ Umurhan, and M.\ de la Torre-Ju\'arez, we compare five general circulation models (GCMs) which have been recently used to study hot extrasolar planet atmospheres (BOB, CAM, IGCM, MITgcm, and PEQMOD), under three test cases useful for assessing model convergence and accuracy. Such a broad, detailed intercomparison has not been performed thus far for extrasolar planets study. The models considered all solve the traditional primitive equations, but employ different numerical algorithms or grids (e.g., pseudospectral and finite volume, with the latter separately in longitude-latitude and ``cubed-sphere'' grids). The test cases are chosen to cleanly address specific aspects of the behaviors typically reported in hot extrasolar planet simulations: 1) steady-state, 2) nonlinearly evolving baroclinic wave, and 3) response to fast timescale thermal relaxation. When initialized with a steady jet, all models maintain the steadiness, as they should---except MITgcm in cubed-sphere grid. A very good agreement is obtained for a baroclinic wave evolving from an initial instability in spectral models (only). However, exact numerical convergence is still not achieved across the spectral models: amplitudes and phases are observably different. When subject to a typical ``hot-Jupiter''-like forcing, all five models show quantitatively different behavior---although qualitatively similar, time-variable, quadrupole-dominated flows are produced. Hence, as have been advocated in several past studies, specific quantitative predictions (such as the location of large vortices and hot regions) by GCMs should be viewed with caution. Overall, in the tests considered here, spectral models in pressure coordinate (PEBOB and PEQMOD) perform the best and MITgcm in cubed-sphere grid performs the worst. [Preview Abstract] |
Monday, November 25, 2013 12:14PM - 12:40PM |
H20.00005: Exploring effects of different dynamical cores in global climate models on regional predictions Invited Speaker: Chris Forest We investigate the uncertainty in regional climate response to patterns of sea surface temperature (SST) anomalies due to multiple sources including the choice of the dynamical core. We quantify the sensitivity of regional climate to localized SST anomaly perturbations via a global teleconnection operator (GTO) \footnote{Li et al. (2012), \textit{J. Geophys. Res.}, \textbf{117}, D20103, doi:10.1029/2011JD017186} (i.e., an empirical Green's function.) Structural uncertainty is sampled in two primary ways. (1) We use versions of the NCAR Community Atmospheric Model (CAM3.1, CAM4, and CAM5) to examine the dependence on the sub-grid scale physics parameterizations. (2) We vary the dynamical cores (spectral, finite volume, and HOMME) for each model. We focus on the seasonal climate response over extensive continental regions as well as global scales. Overall, we can explore the dependence of the GTO on physics parameterizations, model resolution, and dynamical cores and identify regions related to atmospheric circulation patterns that exhibit different response characteristics. We note that initial condition uncertainties require sufficient sample sizes to identify such dependencies. [Preview Abstract] |
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