Momentum flux, flow symmetry, and the nonlinear barotropic governor

Journal Article · Thu Jul 15 04:00:00 EDT 1993 · Journal of the Atmospheric Sciences; (United States)

DOI:https://doi.org/10.1175/1520-0469(1993)050<2159:MFFSAT>2.0.CO;2· OSTI ID:6064773

Nakamura, N ^[1]

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1. Princeton Univ., NJ (United States)

A number of idealized life-cycle simulations of baroclinically unstable waves are systematically analyzed to study the effects of eddy momentum flux and of zonal mean horizontal shear on the finite-amplitude evolution of the waves. Twenty-level quasigeostrophic and primitive equation models with channel geometry are numerically integrated with the most unstable linear normal mode as an initial condition. The flows are inviscid except for weak second-order horizontal diffusion. It is found that the finite-amplitude baroclinic waves are sensitively influenced by the vertically integrated eddy momentum flux of the normal mode via in the large barotropic shear it spins up in the mean flow. This [open quotes]barotropic governor[close quotes] mechanism prevents the eddy from attaining all the available potential energy stored in the domain, leading to irreversible barotropic decay. Only in the purely baroclinic, f-plane, quasigeostrophic problem, where the vertically integrated eddy momentum flux identically vanishes due to symmetry, is the growth of baroclinic waves unaffected by the barotropic governor and bounded solely by the total available potential energy. Barotropic shear in the basic flow, the earth's spherical geometry, and nonquasigeostrophic motion all introduce spatial asymmetry into the normal mode, whose nonlinear evolution therefore rapidly motion all introduce spatial asymmetry into the normal mode, whose nonlinear evolution therefore rapidly departs from the purely baroclinic solution. The details of the departure depend sensitively on the shape of the initial asymmetry, however. The results suggest the natural tendency of baroclinic waves toward barotropic decay in nearly inviscid atmospheres. 32 refs., 12 figs., 1 tab.

• OSTI ID: 6064773
• Journal Information: Journal of the Atmospheric Sciences; (United States), Journal Name: Journal of the Atmospheric Sciences; (United States) Vol. 50:14; ISSN 0022-4928; ISSN JAHSAK
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
540110*
ATMOSPHERIC CIRCULATION
COMPUTERIZED SIMULATION
DISTURBANCES
FLOW MODELS
MATHEMATICAL MODELS
METEOROLOGY
NONLINEAR PROBLEMS
SHEAR
SIMULATION