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Variability in annual mean circulation in southern high latitudes (1997)

Connolley, W. M.

Springer

Climate dynamics 13 (1997), S. 745-756

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ISSN: 1432-0894

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract. Using a hierarchy of climate models together with observations from gridded analyses, I examine the atmosphere-only and coupled ocean-atmosphere variability in the general circulation for the region south of 40 °S. The variability in mean sea level pressure (MSLP) is well simulated by the coupled models. A complication is that the difference between the two analyses used for verification is comparable to the analysis-model differences. An increase in variability is seen within the hierarchy of model runs although even a model without interannual variations in sea surface temperatures (SSTs) captures most of the observed variability. The temporal variation in MSLP in southern high latitudes has a white spectrum consistent with “random” forcing by weather events and a decoupling from oceanic “integration”. In contrast, the spatial pattern of MSLP variability shows large-scale structure that is consistent between observations and various models, even without interannual variation in SSTs. This shows that the models are sufficiently skillful to reproduce the pattern of observed variability and suggests that the pattern of variability is a characteristic of the land-sea distribution and topography.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s003820050195

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Unsymmetric conjugate gradient methods and sparse direct methods in finite element flow simulation (1990)

Howard, D. ; Connolley, W. M. ; Rollett, J. S.

Chichester : Wiley-Blackwell

International Journal for Numerical Methods in Fluids 10 (1990), S. 925-945

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ISSN: 0271-2091

Keywords: Bi-conjugate gradient ; Conjugate gradient ; Conjugate gradient squared ; Finite elements ; Flow simulation ; Preconditioning ; Vector processor ; Frontal solver ; Navier-Stokes ; Boussinesq approximation Newton method ; Picard iteration ; Galerkin method ; Petrov-Galerkin ; Engineering ; Engineering General

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Notes: A series of numerical experiments on the Cray XMP/48 and on the Cray 2 investigate the robustness and economy of direct and unsymmetric conjugate gradient (CG) type methods for the solution of matrix systems arising from a 3D FEM discretization of fluid flow problems. Computations on a Boussinesq flow model problem with either ILU preconditioned or unpreconditioned unsymmetric CG methods are presented. Such experiments seem to indicate that the unpreconditioned BICG method is robust for moderately non-linear incompressible Navier-Stokes FEM discretizations and that the ILU preconditioned BICG method is very robust and more economic than an unsymmetric frontal solver when the generous memory of the Cray 2 is exploited to store both the matrix and its preconditioner. We cover some of the programming aspects of direct and iterative methods on a supercomputer and find that direct methods have advantages: the crucial CPU-consuming area of code is compact but overwhelming, and its percentage of total CPU usage is independent of the spectral properties of the matrix involved. An optimal implementation of the unsymmetric CG method is more difficult because its work is related to the spectral distribution of the matrix considered and because there is no single portion of the code that overwhelmingly dominates the CPU usuage.

Additional Material: 3 Ill.