SIParCS Collection

The goal of the SIParCS program is to make a long-term, positive impact on the quality and diversity of the workforce needed to use and operate 21st century supercomputers. Graduate students and undergraduate students gain significant hands-on experience in high-performance computing and related fields that use HPC for scientific discovery and modeling. This program embeds students as summer interns in the Computational and Information Systems Laboratory, an organization within NCAR charged with provisioning supercomputing and data systems to the geosciences research community.


Pages

A comparison of NCAR application performance on IBM power architectures [presentation]
A comparison of NCAR application performance on IBM power architectures [presentation]
The performance of several of NCAR's climate models was measured on Bluefire and then compared with similar data from Blueice and Bluevista. Both Blueice and Bluevista are Power5 systems, whereas Bluefire is a Power6 system. Differences can be observed between the performance of these different architectures, and new technologies such as Altivec/VMX can be exploited on Bluefire. This work primarily relies on IBM's HPM toolkit to gather hardware counter data. From this counter data, differences in chip performance can be observed.
A conservative semi-Lagrangian discontinuous Galerkin method for transport equation on the cubed-sphere [video]
A conservative semi-Lagrangian discontinuous Galerkin method for transport equation on the cubed-sphere [video]
The discontinuous Galerkin (DG) method is becoming increasingly popular in atmospheric and ocean modeling. However, a major drawback of method is its stringent CFL stability restriction associated with explicit time-stepping, e.g. explicit Runge-Kutta method. In order to get around this issue we adopt a dimension-splitting approach where a regular semi-Lagrangian (SL) scheme is combined with the DG method. The resulting SLDG scheme employs a sequence of 1D operations for solving transport equation on the cubed-sphere. The SLDG scheme is inherently conservative and has the option to incorporate a local positivity-preserving filter for tracers. A novel feature of the SLDG algorithm is that it can be used for multi-tracer transport for global models employing spectral-element grids.
A coordinate based semi-Lagrangian algorithm [presentation]
A coordinate based semi-Lagrangian algorithm [presentation]
In this talk it is shown how an advection algorithm (available in a dycore for example) can be used to create a semi-Lagragian algorithm of arbitrary order of accuracy in time and space using operator integrating factor splitting (OIFS). This algorithm can potentially transport hundreds of tracers with only k-interpolation(s) per tracer per time-step to yield k-th order accuracy in time. The method is more efficient than advecting the the tracers individually after some small number of tracers has been exceeded. This threshold decreases with decreasing order in time and increasing polynomial order and is bounded below by the number of coordinates advected (6 for a sphere). Preliminary results in 1D and 2D are presented where the underlying discretization scheme is the discontinuous Galerkin method (DG) in strong and weak form.
A flux-form version of the conservative semi-Lagrangian multi-tracer transport scheme (CSLAM) [presentation]
A flux-form version of the conservative semi-Lagrangian multi-tracer transport scheme (CSLAM) [presentation]
We present a flux-form modification of a semi-Lagrangian advection scheme that computes the flux of an advected quantity for use in a finite-volume method. The flux-form scheme adds little overhead compared to the semi-Lagrangian method, while also allowing the use of flux limiters to ensure monotonicity of the solution. Using flux limiting is seen to allow better accuracy and convergence rates than monotonicity-ensuring schemes available to semi-Lagrangian schemes, while being much more efficient.
A hybrid estimator for density with extremes [presentation]
A hybrid estimator for density with extremes [presentation]
Extreme weather events that are often important in assessing the impact of climate on our society and the natural environment. To model a non-parametric long tailed distribution, the developed kernel density and logspline method may lack of accuracy in the tails, while the General Pareto Distribution (GPD) do not give the information to the non-extreme section of the data. This study is about a hybrid statistics model combining the logspline method with a parametric GPD tail, by which we can learn about the whole density of the variable and give a more accurate estimation on the probability of the extreme events.
A non-staggered block Jacobi preconditioning strategy in HOMME [presentation]
A non-staggered block Jacobi preconditioning strategy in HOMME [presentation]
Due to parallel implementation, the original block Jacobi preconditioner without any communications for staggered grid in HOMME doesn't work for the non-staggered grid. This report will introduce why the original preconditioner fails for the non-staggered case, the challenges in implementing it, and the basic idea of the algorithm of the non-staggered preconditioner. Comparison with the original preconditioner and analysis will also be addressed at the end.
A two-level non-overlapping optimized Schwarz for spectral elements [presentation]
A two-level non-overlapping optimized Schwarz for spectral elements [presentation]
Semi-implicit time-stepping yields a positive definite Helmholtz problem that needs to be inverted at each time-step. When combined with a semi-Lagrangian approach, the resulting Helmholtz problem can potentially become stiff and the number of iterations required to invert the problem grows without bounds. When discretized in space using spectral elements, it is possible to devise a non-overlapping Schwarz algorithm that uses optimized transmission operators between sub-domains. However, to take care of the stiffness, a coarse solver is required. We report recent results for the Poisson and positive definite Helmholtz operators discretized using 1D and 2D spectral elements.

Pages