Equatorial superrotation and maintenance of the general circulation in two-level models

Journal Article · Sat May 01 04:00:00 EDT 1993 · Journal of the Atmospheric Sciences; (United States)

DOI:https://doi.org/10.1175/1520-0469(1993)050<1211:ESAMOT>2.0.CO;2· OSTI ID:6434177

Saravanan, R ^[1]

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1. Univ. of Cambridge (United Kingdom)

Suarez and Duffy have noted an interesting bifurcation in a two-level gridpoint general circulation model when strong tropical heating is imposed. This bifurcation results in a model climatology with strong upper-level westerlies in the tropics. In this paper, it is argued that this bifurcation is essentially due to the dominant role played by extratropical baroclinic transients in the tropical angular momentum budget. A series of numerical experiments is analyzed with a global two-level primitive equation model, using spectral truncation in the horizontal. The model climatologies in these experiments fall into two categories: (1) conventional, that is, weak upper-level easterlies/westerlies in the tropics; and (2) superrotating, that is, strong upper-level westerlies in the tropics. An attempt is made to explain the maintenance of the general circulation in these two radically different climatologies by studying the properties of unstable normal modes for the two different time-mean states. The spectral characteristics of angular momentum transport due to transient eddies in these two climatologies are also discussed. To understand the meridional propagation of transient eddies, the notion of a [open quotes]modal[close quotes] refractive index in the quasigeostrophic approximation is introduced. From this analysis it is concluded that the conventional climatology is stable to weak perturbations, with the [open quotes]restoring[close quotes] force being provided primarily by extratropical baroclinic eddies. Strong perturbations completely change the propagation characteristics of these eddies, leading to a bifurcation of the general circulation. This has interesting implications for the range of validity of two-level models and the transitivity of tropospheric general circulation. 26 refs., 13 figs., 1 tab.

• OSTI ID: 6434177
• Journal Information: Journal of the Atmospheric Sciences; (United States), Journal Name: Journal of the Atmospheric Sciences; (United States) Vol. 50:9; ISSN 0022-4928; ISSN JAHSAK
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
540110*
ANGULAR MOMENTUM
CLIMATE MODELS
EARTH ATMOSPHERE
GENERAL CIRCULATION MODELS
HEATING
HYPOTHESIS
MATHEMATICAL MODELS
TESTING
TROPICAL REGIONS
TROPOSPHERE
VALIDATION