Clearing Two Atmospheric Modeling Hurdles: Full-Globe Balanced Initialization and an Accurate Steep-Terrain Pressure-Gradient-Force Scheme for the EPIC Model

Details Clearing Two Atmospheric Modeling Hurdles: Full-Globe Balanced Initialization and an Accurate Steep-Terrain Pressure-Gradient-Force Scheme for the EPIC Model Clearing Two Atmospheric Modeling Hurdles: Full-Globe Balanced Initialization and an Accurate Steep-Terrain Pressure-Gradient-Force Scheme for the EPIC Model

Oct 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007dps....39.5509d&link_type=abstract

American Astronomical Society, DPS meeting #39, #55.09; Bulletin of the American Astronomical Society, Vol. 39, p.527

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The EPIC Atmospheric model's new vertical coordinate is a smooth blend between an isentropic coordinate aloft and a terrain-following, pressure (sigma) coordinate at depth. This hybrid coordinate is the key feature that enables the model to accurately simulate both gas-giant-class and terrestrial-class atmospheres. Two long-standing technical challenges exist related to the sigma coordinate that we are now addressing. The first affects initialization, in which the goal is to balance the mass and momentum (pressure and wind) fields of the three-dimensional initial condition to minimize the generation of spurious gravity waves. We have adapted the elliptic inversion scheme developed for the sigma coordinate by Wang (1995, Mon. Wea. Rev. 123, 482-488) to our hybrid coordinate and show applications to Jupiter. This provides the EPIC model with the new functionality of being able to initialize balanced structures that straddle the equator, most notably equatorial waves. The second challenge is that the terrain-following coordinate splits the horizontal pressure-gradient force (PGF) into two parts, which in steep terrain creates a difference-of-large-numbers problem (incomplete cancellation of truncation errors) that generates spurious winds. This issue plagues both atmospheric and oceanic modelers and we have encountered it for Venus in superrotation spinup experiments with topography (Herrnstein and Dowling, 2007, JGR 112, E04S08). A promising new approach is to consider finite-volume algorithms for the PGF. Chu and Fan (2003, JGR 108) have recently shown that a two-dimensional, finite-volume implementation alleviates the problems for sigma-coordinate ocean models. We are expanding on this to a full three-dimensional, finite-volume PGF algorithm for the EPIC model and show our latest results. This research is supported by the NASA Planetary Atmospheres and Outer Planets Research Programs and the NSF Planetary Astronomy Program.

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