Capability Development for Planetary General Circulation Model, 15-R9807Printer Friendly Version
Inclusive Dates: 04/01/08 Current
Background - Most of the planets and several moons in our Solar System have an atmosphere. A general circulation model (GCM; a global scale model that simulates the large scale behavior of an atmosphere) is the most complete tool available to comprehensively model these atmospheres. This project builds on SwRI's expertise in planetary atmosphere modeling through the development of a unified "next-generation" general circulation model for simulating the atmospheres of solid-body planets and moons. In addition to modeling Earth's atmosphere, the new model will have the capability to simulate thick atmospheres (Venus, Titan), thin atmospheres (Mars), and tenuous atmospheres (Pluto, Triton).
Approach - The work involves modifying a newly developed and publicly available GCM dynamical core the Flexible Modeling System (FMS) developed at the Geophysical Fluid Dynamics Laboratory. The core in its current configuration is used to study the Earth's atmosphere. Minor changes are required to switch the basic parameters (e.g., gravitational acceleration, pressure/temperature structure, atmospheric composition, rotation rate and planetary dimension) from one planet to another. The bulk of the project involves conducting detailed model core tests for a range of planetary constants and then gradually adding more complex but sufficiently generalized physics appropriate for the wide range of planetary atmospheres. Physics packages include radiative transfer, cloud microphysics, boundary layer and surface processes and moist convection. Capability demonstration will be achieved by using the new model to study the Martian CO2, H2O, and dust cycles and the seasonal haze cycle on Titan.
Accomplishments - We have made significant progress in building the physics packages. A stand-alone, radiative transfer code, which includes Rayleigh scattering, absorption of atmospheric gases, and the effects of aerosol particles, has been developed. The code was tested with the case of a static haze profile in Titan's atmosphere and accurately reproduced the attenuation of solar wavelengths by the main haze layer. An orbital package was written to compute the correct Sun-planet distance and compared to data on Martian solstice and equinox dates. The microphysics package is in development and currently handles vertical transport and coagulation of involatile aerosol particles (e.g., dust or Titan haze). The time manager from the FMS package was modified to accurately store times in a lossless, integer-based format such that non-terrestrial diurnal and annual periods can now be tracked. Additional code infrastructure developments include a more general and adaptable directory structure, generalized model initialization routines, and the configuration of the model diagnostic and output routines to produce the types and frequency of output information needed for testing and analysis.