Dynamics of the West African Monsoon. Part IV: Analysis of 25–90-Day Variability of Convection and the Role of the Indian MonsoonSource: Journal of Climate:;2009:;volume( 022 ):;issue: 006::page 1541Author:Janicot, Serge
,
Mounier, Flore
,
Hall, Nicholas M. J.
,
Leroux, Stéphanie
,
Sultan, Benjamin
,
Kiladis, George N.
DOI: 10.1175/2008JCLI2314.1Publisher: American Meteorological Society
Abstract: This paper is part of a series of studies addressing the dynamics of the West African summer monsoon at intraseasonal time scales between 10 and 90 days. The dominant mode of 25?90-day convective variability in the African monsoon was investigated, starting from previous results involving the excitation of dry equatorial Kelvin and Rossby waves by a negative diabatic heat source located over the warm pool. This evolution is consistent with a significant contribution by a convectively coupled equatorial Rossby wave and the MJO. On the other hand, convectively coupled Kelvin waves as well as the dry Kelvin wave signal have a very weak impact. However, there is more to the global control of the African summer monsoon than convectively coupled wave dynamics. The active/break cycle of the Indian monsoon, controlled by a northward-moving dipole of diabatic heating in the Indian sector, can also influence the African monsoon through atmospheric teleconnections. Simulations performed with a dry primitive equation model show that this influence may be transferred through the northern Indian heat source, which excites a Rossby cyclonic circulation propagating westward over North Africa that is cut off by the northward arrival of the equatorial Indian heat source and the associated intrusion of an anticyclonic ridge. Low-level westerly winds and moisture advection within the ITCZ consequently increase over Africa. The mean time lag between an active phase over India and over Africa is about 15?20 days.
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contributor author | Janicot, Serge | |
contributor author | Mounier, Flore | |
contributor author | Hall, Nicholas M. J. | |
contributor author | Leroux, Stéphanie | |
contributor author | Sultan, Benjamin | |
contributor author | Kiladis, George N. | |
date accessioned | 2017-06-09T16:23:53Z | |
date available | 2017-06-09T16:23:53Z | |
date copyright | 2009/03/01 | |
date issued | 2009 | |
identifier issn | 0894-8755 | |
identifier other | ams-67135.pdf | |
identifier uri | http://onlinelibrary.yabesh.ir/handle/yetl/4208549 | |
description abstract | This paper is part of a series of studies addressing the dynamics of the West African summer monsoon at intraseasonal time scales between 10 and 90 days. The dominant mode of 25?90-day convective variability in the African monsoon was investigated, starting from previous results involving the excitation of dry equatorial Kelvin and Rossby waves by a negative diabatic heat source located over the warm pool. This evolution is consistent with a significant contribution by a convectively coupled equatorial Rossby wave and the MJO. On the other hand, convectively coupled Kelvin waves as well as the dry Kelvin wave signal have a very weak impact. However, there is more to the global control of the African summer monsoon than convectively coupled wave dynamics. The active/break cycle of the Indian monsoon, controlled by a northward-moving dipole of diabatic heating in the Indian sector, can also influence the African monsoon through atmospheric teleconnections. Simulations performed with a dry primitive equation model show that this influence may be transferred through the northern Indian heat source, which excites a Rossby cyclonic circulation propagating westward over North Africa that is cut off by the northward arrival of the equatorial Indian heat source and the associated intrusion of an anticyclonic ridge. Low-level westerly winds and moisture advection within the ITCZ consequently increase over Africa. The mean time lag between an active phase over India and over Africa is about 15?20 days. | |
publisher | American Meteorological Society | |
title | Dynamics of the West African Monsoon. Part IV: Analysis of 25–90-Day Variability of Convection and the Role of the Indian Monsoon | |
type | Journal Paper | |
journal volume | 22 | |
journal issue | 6 | |
journal title | Journal of Climate | |
identifier doi | 10.1175/2008JCLI2314.1 | |
journal fristpage | 1541 | |
journal lastpage | 1565 | |
tree | Journal of Climate:;2009:;volume( 022 ):;issue: 006 | |
contenttype | Fulltext |