John M. Dennis

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In this paper, we describe how inverse space-filling curve partitioning is used to increase the simulation rate of a global ocean model. Space-filling curve partitioning allows for the elimination of load imbalance in the computational grid due to land points. Improved load balance combined with code modifications within the conjugate gradient solver(More)
The Community Atmosphere Model (CAM) version 5 includes a spectral element dynamical core option from NCAR’s High-Order Method Modeling Environment. It is a continuous Galerkin spectral finite element method designed for fully unstructured quadrilateral meshes. The current configurations in CAM are based on the cubedsphere grid. The main motivation for(More)
Climate modeling is a grand challenge problem where scientific progress is measured not in terms of the largest problem that can be solved but by the highest achievable integration rate. These models have been notably absent in previous Gordon Bell competitions due to their inability to scale to large processor counts. A scalable and efficient spectral(More)
Numerical methods for solving the systems of partial differential equations arising in geophysical fluid dynamics rely on a variety of spatial discretization schemes (e.g. finite difference, finite element). For parallel execution on distributed memory computers, the computational domain must be partitioned. The choice of partitioning algorithm can have a(More)
The increasing gap between processor performance and memory access time warrants the re-examination of data movement in iterative linear solver algorithms. For this reason, we explore and establish the feasibility of modifying a standard iterative linear solver algorithm in a manner that reduces the movement of data through memory. In particular, we present(More)
We first demonstrate the parallel performance of the dynamical core of a spectral element atmospheric model. The model uses continuous Galerkin spectral elements to discretize the surface of the Earth, coupled with finite differences in the radial direction. Results are presented from two distributed memory, mesh interconnect supercomputers (ASCI Red and(More)
We describe the design and implementation of an application-level parallel I/O (PIO) library for the reading and writing of distributed arrays to several common scientific data formats. PIO provides the flexibility to control the number of I/O tasks through data rearrangement to an I/O friendly decomposition. This flexibility enables reductions in per task(More)
An efficient and scalable discontinuous Galerkin shallow water model on the cubed sphere is developed by extending the transport scheme of Nair et al. (2005). The continuous flux form nonlinear shallow water equations in curvilinear coordinates are developed. Spatial discretization is a nodal basis set of Legendre polynomials. Fluxes along internal element(More)
An interpolation based non-conforming spectral element atmospheric model is described. The error norms for a standard test problem are compared against uniform resolution results. Preliminary results for an adaptive mesh refinement strategy are reported. To avoid local time-stepping, a nonlinear variant of operator integration factor splitting has been(More)