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Mechanism of the Northward-Propagating Intraseasonal Oscillation: Insights from a Zonally Symmetric Model *

Mechanism of the Northward-Propagating Intraseasonal Oscillation: Insights from a Zonally... The propagation and initiation mechanisms of the boreal summer intraseasonal oscillation (BSISO) in the south Asian summer monsoon are examined with a zonally symmetric atmospheric model. In the axially symmetric model the effects of zonally propagating atmospheric waves are intentionally excluded. The model specifies mean flows and depicts the lowest baroclinic mode and a barotropic mode in the free troposphere. The two vertical modes are coupled by the time-mean vertical wind shear. The model atmosphere produces a 15–20-day oscillation, which is characterized by northward propagation of convection from south of the equator to the Indian monsoon trough region and a reinitiation of convection in the region between 10°S and the equator. The northward propagation in the model is produced by the free troposphere barotropic divergence, which leads convection by about a quarter of a cycle. The vertical advection of summer-mean easterly vertical wind shear by perturbation vertical motion inside the convective region induces barotropic divergence (convergence) to the north (south) of convection. This barotropic divergence triggers the moisture convergence in the boundary layer to the north of convection, causing the northward propagation of precipitation. The development of convection in the Southern Hemisphere near the equator is also produced by the development of the barotropic divergence in the free troposphere. When the BSISO convection is located in the Indian monsoon trough region, it creates Hadley-type anomalous circulation. This Hadley-type circulation interacts with the monsoon flow through the meridional and vertical advections creating anomalous barotropic divergence and boundary layer convergence. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Climate American Meteorological Society

Mechanism of the Northward-Propagating Intraseasonal Oscillation: Insights from a Zonally Symmetric Model *

Drbohlav, Hae-Kyung Lee; Wang, Bin
Journal of Climate , Volume 18 (7) – Jul 9, 2003
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References (28)

Publisher
American Meteorological Society
Copyright
Copyright © 2003 American Meteorological Society
ISSN
1520-0442
DOI
10.1175/JCLI3306.1
Publisher site
See Article on Publisher Site

Abstract

The propagation and initiation mechanisms of the boreal summer intraseasonal oscillation (BSISO) in the south Asian summer monsoon are examined with a zonally symmetric atmospheric model. In the axially symmetric model the effects of zonally propagating atmospheric waves are intentionally excluded. The model specifies mean flows and depicts the lowest baroclinic mode and a barotropic mode in the free troposphere. The two vertical modes are coupled by the time-mean vertical wind shear. The model atmosphere produces a 15–20-day oscillation, which is characterized by northward propagation of convection from south of the equator to the Indian monsoon trough region and a reinitiation of convection in the region between 10°S and the equator. The northward propagation in the model is produced by the free troposphere barotropic divergence, which leads convection by about a quarter of a cycle. The vertical advection of summer-mean easterly vertical wind shear by perturbation vertical motion inside the convective region induces barotropic divergence (convergence) to the north (south) of convection. This barotropic divergence triggers the moisture convergence in the boundary layer to the north of convection, causing the northward propagation of precipitation. The development of convection in the Southern Hemisphere near the equator is also produced by the development of the barotropic divergence in the free troposphere. When the BSISO convection is located in the Indian monsoon trough region, it creates Hadley-type anomalous circulation. This Hadley-type circulation interacts with the monsoon flow through the meridional and vertical advections creating anomalous barotropic divergence and boundary layer convergence.

Journal

Journal of Climate – American Meteorological Society

Published: Jul 9, 2003

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