Effect of overturning circulation on long equatorial waves: a low frequency cutoff

Effect of overturning circulation on long equatorial waves: a low frequency cutoff AbstractZonally long tropical waves in the presence of a large-scale meridional and vertical overturning circulation are studied in an idealized model based on the Intraseasonal Multiscale Moist Dynamics (IMMD) theory. The model consists of a system of shallow water equations describing barotropic and first baroclinic vertical modes coupled to one another by the zonally symmetric, time independent background circulation. In order to isolate the effects of the meridional circulation alone, an idealized background flow is chosen to mimic the meridional and vertical components of the flow of the Hadley cell; the background flow meridionally converges and rises at the equator. The resulting linear eigenvalue problem is a generalization of the long wave-scaled version of Matsuno’s equatorial wave problem with the addition of meridional and vertical advection. The results demonstrate that the meridional circulation couples equatorially-trapped baroclinic Rossby waves to planetary, barotropic free Rossby waves. The meridional circulation also causes the Kelvin wave to develop an equatorially trapped barotropic component, imparting a westwardtilted vertical structure to the wave. The total energy of the linear system is positive definite, so all waves are shown to be neutrally stable. A critical layer exists at latitudes where the meridional background flow vanishes, resulting in a minimum frequency cut-off for physically feasible waves. Therefore, linear Matsuno waves with periods longer than the vertical transport time of the meridional circulation do not exist in the equatorial waveguide. This implies a low frequency cutoff for long equatorial waves. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of the Atmospheric Sciences American Meteorological Society

Effect of overturning circulation on long equatorial waves: a low frequency cutoff

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Publisher
American Meteorological Society
Copyright
Copyright © American Meteorological Society
ISSN
1520-0469
D.O.I.
10.1175/JAS-D-17-0173.1
Publisher site
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Abstract

AbstractZonally long tropical waves in the presence of a large-scale meridional and vertical overturning circulation are studied in an idealized model based on the Intraseasonal Multiscale Moist Dynamics (IMMD) theory. The model consists of a system of shallow water equations describing barotropic and first baroclinic vertical modes coupled to one another by the zonally symmetric, time independent background circulation. In order to isolate the effects of the meridional circulation alone, an idealized background flow is chosen to mimic the meridional and vertical components of the flow of the Hadley cell; the background flow meridionally converges and rises at the equator. The resulting linear eigenvalue problem is a generalization of the long wave-scaled version of Matsuno’s equatorial wave problem with the addition of meridional and vertical advection. The results demonstrate that the meridional circulation couples equatorially-trapped baroclinic Rossby waves to planetary, barotropic free Rossby waves. The meridional circulation also causes the Kelvin wave to develop an equatorially trapped barotropic component, imparting a westwardtilted vertical structure to the wave. The total energy of the linear system is positive definite, so all waves are shown to be neutrally stable. A critical layer exists at latitudes where the meridional background flow vanishes, resulting in a minimum frequency cut-off for physically feasible waves. Therefore, linear Matsuno waves with periods longer than the vertical transport time of the meridional circulation do not exist in the equatorial waveguide. This implies a low frequency cutoff for long equatorial waves.

Journal

Journal of the Atmospheric SciencesAmerican Meteorological Society

Published: Mar 7, 2018

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