CISL Annual Report 2005 > CISL research accomplishments

Numerical methods: HOMME status

The CISL Computational Science Section's (CSS) High-Order Method Modeling Environment (HOMME) provides a foundation for building a new generation of general atmospheric circulation models for the atmospheric science community. HOMME is CSS's vehicle to investigate the suitability of using high-order-element-based methods to build conservative and accurate dynamical cores that efficiently scale to hundreds-of-thousands of processors, achieve scientifically useful integration rates, and can easily couple to community physics packages. This research is sponsored by the Department of Energy's Climate Change Prediction Program (CCPP) and Scientific Discovery through Advanced Computing (SciDAC) programs, and is done in partnership with Sandia National Laboratories, IBM, the University of Colorado, and NCAR's Climate and Global Dynamics and Mesoscale (CGD) and Microscale Meteorology (MMM) Divisions.

Over the past year the Section's focus has been on exploring conservative high-order methods, integrating physics packages into HOMME, incorporating spatial adaptivity, investigating modern time-stepping schemes, and researching scalable solver technology.

The discontinuous Galerkin (DG) method is a hybrid approach combining the finite-volume and the finite-element methods, and is ideally suited for atmospheric numerical modeling because it is inherently conservative. Moreover, high-order DG methods retain all the advantages of the spectral element method (e.g., exponential convergence, computational efficiency, and parallel scalability), upon which HOMME is built. In the past year, both modal and nodal versions of the DG model on the cubed sphere have been integrated into HOMME and validated using the Williamson shallow water test suite (JCP, 1992). The DG version of HOMME has been ported to numerous architectures, and initial scaling results out to 2,048 processors of the IBM Blue Gene system frost are promising. For additional details, see SciDAC-CCPP.

CSS has been working to integrate three physics schemes into HOMME: Emanuel physics, Community Atmospheric Model Version 2 (CAM-2) physics, and Cloud Resolving Convective parameterization (CRCP) physics. Initial testing of a moist spectral element model capable of running an aqua planet test case was performed using Emanuel physics. Aqua planet is an idealization based on an earth-like planet covered completely in water, and is of interest because it is complex enough to fully exercise a substantial portion of the atmospheric physics packages attached to the moist dynamics while remaining relatively simple to implement. The aqua planet test case was run on a 32-rack IBM Blue Gene system at Rochester, Minnesota and achieved 11.3 TF on 32,768 processors. Additional details are available at HOMME on the IBM BlueGene/L.

This image depicts the transport of moisture into a 3D flow around the surface of the Earth. The surfaces represent identical concentrations of water in the air. The colors on the surfaces represent temperature. Moisture transport is one of the most important aspects of climate modeling. The study of idealized test cases using simplified physics in HOMME might help researchers identify which physical processes are responsible for triggering certain phenomena observed in our planet's climate.