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- Title
The Finite-Amplitude Evolution of Mixed Kelvin--Rossby Wave Instability and Equatorial Superrotation in a Shallow-Water Model and an Idealized GCM.
- Authors
ZURITA-GOTOR, PABLO; HELD, ISAAC M.
- Abstract
An instability involving the resonant interaction of a Rossby wave and a Kelvin wave has been proposed to drive equatorial superrotation in planetary atmospheres with a substantially smaller radius or a smaller rotation rate than Earth, that is, with a large thermal Rossby number. To pursue this idea, this paper investigates the equilibration mechanism of Kelvin--Rossby instability by simulating the unforced initial-value problem in a shallow-water model and in a multilevel primitive equation model. Although the instability produces equatorward momentum fluxes in both models, only the multilevel model is found to superrotate. It is argued that the shortcoming of the shallow-water model is due to its difficulty in representing Kelvin wave breaking and dissipation, which is crucial for accelerating the flow in the tropics. In the absence of dissipation, the zonal momentum fluxed into the tropics is contained in the eddy contribution to the mass-weighted zonal wind rather than the zonal-mean zonal flow itself. In the shallow-water model, the zonal-mean zonal flow is only changed by the eddy potential vorticity flux, which is very small in our flow in the tropics and can only decelerate the flow in the absence of external vorticity stirring.
- Subjects
ROSSBY waves; OCEAN waves; ROSSBY number; INITIAL value problems; SHALLOW-water equations; ZONAL winds; VORTEX motion
- Publication
Journal of the Atmospheric Sciences, 2018, Vol 75, Issue 7, p2299
- ISSN
0022-4928
- Publication type
Article
- DOI
10.1175/JAS-D-17-0386.1