Zonal flow vacillation and eddy forcing in a simple GCM of the atmosphere. [GCM (general circulation model)]

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

DOI:https://doi.org/10.1175/1520-0469(1993)050<3244:ZFVAEF>2.0.CO;2· OSTI ID:5705347

Yu, Jin-Yi; Hartmann, D L ^[1]

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1. Univ. of Washington, Seattle, WA (United States)

Zonal flow vacillation with long time scales is observed in a 3070-day simple GCM simulation with zonally symmetric forcing. Wave-mean flow interactions are investigated by composite analysis and transform Eulerian momentum budget analysis. Nonlinear life-cycle simulations are conducted to demonstrate that each extreme phase of the zonal flow vacillation is a quasi stable state and is self-maintained by embedded synoptic eddies. Transformed Eulerian momentum budget analyses show that the differences of wave propagation between two extreme phases result in the anomalous eddy forcing needed to maintain zonal wind anomalies against frictional damping. Budget analyses also indicate that eddy momentum flux convergence is the major positive forcing in both the extreme and transition phases. The major balance during the index cycle is between eddy barotropic forcing and residual circulation forcing in the upper troposphere and between residual circulation forcing and frictional damping in the lower troposphere. Further comparisons of eddy forcing from various time-scale eddies show that the anomalous eddy forcing is primarily provided by synoptic time scales. Two nonlinear life-cycle simulations, strated separately form the composite zonal flows of the two extreme phases and small-amplitude wavenumber 6 perturbations, display the intensification of initial wind anomalies by the growing eddies. A dual-jet stream structure appears in the life-cycle simulation strated from the high index composite, and a more intense single jet stream structure evolves from the low index initial state. It is noticed that maximum wind anomalies are established earlier at higher latitudes than at lower latitudes. This suggests that the mechanisms triggering transitions from one self-maintained phase to the other operate at higher latitudes. It is suspected that barotropic instability/stability is a possible triggering mechanism for transition from one state to another. 25 refs., 17 figs.

• OSTI ID: 5705347
• Journal Information: Journal of the Atmospheric Sciences; (United States), Journal Name: Journal of the Atmospheric Sciences; (United States) Vol. 50:19; ISSN 0022-4928; ISSN JAHSAK
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
540110*
AIR FLOW
ATMOSPHERIC CIRCULATION
EARTH ATMOSPHERE
FLUID FLOW
GAS FLOW
GENERAL CIRCULATION MODELS
GRAVITY WAVES
MATHEMATICAL MODELS
METEOROLOGY
NONLINEAR PROBLEMS
WAVE PROPAGATION
WIND