Nonlinear equilibration of localized instabilities on a baroclinic jet

Journal Article · Mon Aug 01 04:00:00 EDT 1994 · Journal of the Atmospheric Sciences; (United States)

DOI:https://doi.org/10.1175/1520-0469(1994)051<2270:NEOLIO>2.0.CO;2· OSTI ID:6795313

DelSole, T M; Farrell, B F ^[1]

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1. Harvard Univ., Cambridge, MA (United States)

Dynamical mechanisms underlying the equilibration of absolute instability are examined in a nonlinear, quasigeostrophic, two-layer model. The key to understanding the nonlinear equilibration is in recognizing that linear absolute instabilities can be stabilized by a reduction of the vertical shear and by enhancement of the mean barotropic velocity. In a localized domain, the equilibration process proceeds with the creation of locally convectively unstable regions downstream, which encroach onto the locally absolutely unstable region until the local instability is suppressed. That local instabilities exist only if absolutely unstable regions span a minimum size is verified by eigenvalue calculations of three-dimensional flows. Numerical examples suggest that this critical size is at least 9000 km for a wide range of parameter values chosen to investigate the midlatitude storm tracks. Fluctuations arising from local absolute instability obtain maximum amplitude in the downstream convectively unstable regions rather than in the absolutely unstable regions themselves. Together, these results suggest that if an equilibrated absolute instability were to occur in midlatitudes, a zonal band of surface easterlies exceeding 9000 km would be required and the associated enhanced variances would not be found coincident with the regions of absolute instability. 28 refs., 21 figs., 1 tab.

• DOE Contract Number: FC03-90ER61010
• OSTI ID: 6795313
• Journal Information: Journal of the Atmospheric Sciences; (United States), Journal Name: Journal of the Atmospheric Sciences; (United States) Vol. 51:15; ISSN 0022-4928; ISSN JAHSAK
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
540110*
ATMOSPHERIC CIRCULATION
INSTABILITY
MATHEMATICAL MODELS
NONLINEAR PROBLEMS