Longitudinal variability of the zonal and meridional circulation and the intensity of planetary waves in the lower and middle atmosphere
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Atmospheric Circulation
Zonal flow (plasma)
Abstract A series of zonal currents in the Pacific Ocean is investigated using eddy-permitting ocean general circulation models. The zonal currents in the subsurface are classified into two parts: one is a series of broad zonal flows that has the meridional pattern slanting poleward with increasing depth and the other is finescale zonal jets with the meridional scale of 3°–5° formed in each broad zonal flow. The basic pattern for the broad zonal flows is similar between the coarse-resolution model and the eddy-permitting model and is thought to be the response to the wind forcing. A part of the zonal jets embedded in each zonal flow is explained by the anomalous local wind forcing. Most of them, however, seem to be mainly created by the rectification of turbulent processes on a β plane (the Rhines effect), and zonal jets in this study have common features with the zonally elongated flows obtained in previous modeling studies conducted in idealized basins. The position of zonal jets is not stable when the ocean floor is flat, whereas it oscillates only within a few degrees under realistic bottom topography.
Zonal flow (plasma)
Forcing (mathematics)
Circulation (fluid dynamics)
Eddy
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An exploratory study of approximations for the equatorial region is given to stress the rapid variation of coriolis parameter with latitude, and the consequential differences in the length scales in meridional and zonal directions. The resulting equations retain coriolis as well as non-linear inertia terms in zonal momentum balance. This approximation for dominantly zonal flow is supplemented with another for a sublayer near the equator where the meridional flow might be dominant in case of large interhemispheric transport, as in monsoon over the Indian Ocean.
Zonal flow (plasma)
Meridional flow
Momentum (technical analysis)
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Zonal flow (plasma)
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Abstract The derivation of the meridional momentum flux arising from a multiscale horizontal velocity field in the intraseasonal, planetary, equatorial synoptic-scale dynamics (IPESD) multiscale models of the equatorial troposphere is presented. It is shown that, because of the balance dynamics on the synoptic scales, the synoptic-scale component of the meridional momentum flux convergence must always vanish at the equator. Plausible Madden–Julian oscillation (MJO) models are presented along with their planetary-scale meridional momentum fluxes. These models are driven by synoptic-scale heating fluctuations that have vertical and meridional tilts. Irrespective of the sign of the synoptic-scale meridional momentum flux (direction of the tilts) in each of the four MJO examples, the zonal and vertical mean meridional momentum flux convergence from the planetary scales always drives westerly winds near the equator: this is the superrotation characteristic of actual MJOs. The concluding discussion demonstrates that equatorial superrotation occurs when the planetary flow due to the vertical upscale momentum flux from synoptic scales reinforces the horizontally convergent flow due to planetary-scale mean heating.
Madden–Julian oscillation
Zonal flow (plasma)
Momentum (technical analysis)
Synoptic scale meteorology
Meridional flow
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An exploratory study of approximations for the equatorial region is given to stress the rapid variation of coriolis parameter with latitude, and the consequential differences in the length scales in meridional and zonal directions. The resulting equations retain coriolis as well as non-linear inertia terms in zonal momentum balance. This approximation for dominantly zonal flow is supplemented with another for a sublayer near the equator where the meridional flow might be dominant in case of large interhemispheric transport, as in monsoon over the Indian Ocean.
Zonal flow (plasma)
Momentum (technical analysis)
Meridional flow
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Zonal flow (plasma)
Meridional flow
Wavenumber
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Zonal flow (plasma)
Boundary current
Wavenumber
Mean flow
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Multiple alternating zonal jets observed in the ocean are studied with an idealized quasigeostrophic model of flow in a zonal channel. The jets are maintained by the eddies generated by the imposed, supercritical background flow. The formation, nonlinear dynamics and equilibration of the jets are explained in terms of linear stability arguments and nonlinear self-interactions of the linear eigenmodes. In the proposed mechanism, energy of the background flow is released to the primary instability mode with long meridional and short zonal length scales. This mode undergoes secondary, transverse instability that sets the meridional scale of the emerging multiple zonal jets. This instability channels energy into several weakly damped zonal eigenmodes that amplify the jets. The emerging jets feed back on the instabilities through the partial meridional localization of the most unstable eigenmodes.
Eddy
Zonal flow (plasma)
Supercritical flow
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