Multi-scale waves in sound-proof global simulations with EULAG |
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| Authors: | Joseph M Prusa William J Gutowski |
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| Institution: | (1) Colorado Research Associates Division, NorthWest Research Associates, Boulder, CO, USA;(2) NorthWest Research Associates/Colorado Research Associates Division, Boulder, CO, USA |
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| Abstract: | EULAG is a computational model for simulating flows across a wide range of scales and physical scenarios. A standard option
employs an anelastic approximation to capture nonhydrostatic effects and simultaneously filter sound waves from the solution.
In this study, we examine a localized gravity wave packet generated by instabilities in Held-Suarez climates. Although still
simplified versus the Earth’s atmosphere, a rich set of planetary wave instabilities and ensuing radiated gravity waves can arise. Wave packets
are observed that have lifetimes ≤ 2 days, are negligibly impacted by Coriolis force, and do not show the rotational effects
of differential jet advection typical of inertia-gravity waves. Linear modal analysis shows that wavelength, period, and phase
speed fit the dispersion equation to within a mean difference of ∼ 4%, suggesting an excellent fit. However, the group velocities
match poorly even though a propagation of uncertainty analysis indicates that they should be predicted as well as the phase
velocities. Theoretical arguments suggest the discrepancy is due to nonlinearity — a strong southerly flow leads to a critical
surface forming to the southwest of the wave packet that prevents the expected propagation. |
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