``Multidisciplinary Space Science Simulation in a Distributed Heterogeneous Environment''
Dr. Geoff Crowley, Dr. Christopher J. Freitas, Aaron Ridley, David Winningham, Richard Murphy, and Richard Link
Southwest Research Institute, San Antonio, TX 78238-5166
E-mail: crowley@picard.space.swri.edu
URL: http://espsun.space.swri.edu/spacephysics/home.html

The Earth's space environment includes the middle atmosphere at altitudes of about 50 km, through the upper atmosphere and magnetosphere, to the solar wind and ultimately to the Sun itself. The solar wind streams out from the sun at speeds of several hundred kilometers per second, carrying energetic particles and its own magnetic field (the Interplanetary Magnetic Field, IMF). The magnetosphere (the magnetic cavity surrounding the Earth) protects the atmosphere from direct bombardment by most of these particles. The magnetosphere accumulates energy through its interaction with the solar wind. Periodically, the energy is released in the form of particle precipitation, strong electric fields and large currents flowing in the ionosphere at high latitudes. The particle precipitation causes bright aurorae in both the Northern and Southern hemispheres. The large currents produce perturbations in the magnetic field measured at the Earth's surface, resulting in the phenomenon known as a magnetic storm. The large amount of energy and momentum deposited in the thermosphere and ionosphere during magnetic storms changes the global circulation patterns, density, temperature and composition above about 100 km altitude. Some of the most energetic particles penetrate to lower altitudes, where they alter the mesospheric and stratospheric chemistry.

The term ``space-weather'' refers to conditions on the sun, in the solar wind, magnetosphere, ionosphere, thermosphere, and mesosphere, that can influence the performance and reliability of space-borne and ground-based technological systems and can endanger human life or health. The Nation's reliance on advanced technological systems is growing exponentially, and many of these systems are susceptible to failure or unreliable performance because of extreme space-weather. Adverse conditions in the space environment can cause disruption of communications, navigation, electric power distribution grids, and satellite operations, leading to a broad range of socio-economic losses. The National Space Weather Program (NSWP) is a new initiative designed to address many of the unresolved aspects of space weather (including theory, modeling and measurements) in a unified manner. The NSWP initiative is jointly funded by the Air Force, Navy, NSF and NASA. One of the goals of the NSWP is to produce weather forecasts for the various regions of space ranging from the sun to the Earth's middle atmosphere. The NSWP has the potential to make important contributions to the safety and reliable operation of many technological assets ranging from communication satellites to transformers on industrial power distribution grids. The NSWP needs new capabilities in modeling if it is to achieve its forecasting goals.

Southwest Research Institute (SwRI) is developing a space weather model spanning the mesosphere, ionosphere and thermosphere. The new model is based on an existing computer code which runs on CRAY Supercomputers at the National Center for Atmospheric Research (NCAR). This code is called the Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM), and is widely acknowledged as the premier space weather code in existence. The TIME-GCM predicts winds, temperatures, major and minor composition, and electrodynamic quantities globally from 30 km to about 500 km. It does this by solving the momentum, hydrostatic, energy and continuity equations with the appropriate physics and chemistry for each altitude. The current model uses a fixed geographic grid with a 5 x 5 degrees horizontal resolution, and a vertical resolution of half a pressure scale height. This fixed grid size restricts the number of geophysical problems which can be addressed with the NCAR-TIMEGCM. The code is being modified at SwRI to run in a distributed parallel computing environment, and will be enhanced by providing a variable grid size capability to permit mesoscale science problems to be addressed that are not within the current model's capability.

The Research Initiative Program in Advanced Modeling and Simulation (RIP-AMS) was an inter-divisional collaboration at SwRI which resulted in the enhancement and expansion of SwRI capabilities in high performance parallel computing. The RIP-AMS program resulted in parallel computing techniques which permit significant improvements in the runtime of computer codes. Specifically, algorithms based on domain decomposition strategies have been developed, providing a framework which will be applied to the TIME-GCM code, allowing a natural method for parallelization and incorporation of variable grid size regions. The message passing control system used in the RIP-AMS is based on the Parallel Virtual Machine (PVM) library. Here, PVM provides a control environment which seamlessly couples together different workstations, providing a common data communication format and system control over the message passing process. The SwRI heterogeneous parallel virtual machine consists of 40 high end workstations connected by a 155 Mb/s fibre-optic ATM network.

We are also planning to couple the SwRI parallelized TIMEGCM to models of the inner magnetosphere and the solar wind located at different locations, extending the virtual machine across the continental US. The challenges of these ambitious projects will be outlined.