Dynamics of subtropical vertical motions over the Americas during El Niño boreal winters

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Main Author:	V. Magaña
Format:	Artículo científico
Language:	en
Published:	Universidad Nacional Autónoma de México 2005
Subjects:	Biología ENOS Rossby waves precipitation vertical motion
Online Access:	Acceder al recurso
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author	V. Magaña
author_facet	V. Magaña
contents	Dynamics of subtropical vertical motions over the Americas during El Niño boreal winters V. Magaña T. Ambrizzi Biología ENOS Rossby waves precipitation vertical motion On the average, during boreal winter (December through February), the occurrence of El Niño/SouthernOscillation (ENSO) results in enhanced or diminished precipitation in various regions of the Americas.Anomalous convective activity in the central-eastern Pacific forces quasi-stationary Rossby waves thatfollow paths to the Northern and Southern hemispheres. The so-called Pacific-North American (PNA) patternresults in ascending motion and enhanced precipitation over California and the Gulf of Mexico. The PNA alsoaffects the Caribbean Sea by inhibiting winter tropical convection due to subsidence. In the SouthernHemisphere (SH), a weak quasi-stationary wave train is observed over southeast South America that resultsin enhanced ascending motion and precipitation. Over the equatorial region, the descending branch of astationary Kelvin wave inhibits convective activity over northeastern Brazil and other parts of northernSouth America. However, there are well known differences in the El Niño signal from one event to another inwhat is known as inter-ENSO variability. Through quasi-geostrophic analyses, the anomalous vertical motionsassociated with the quasi-stationary Rossby waves may be separated from those associated with the stationaryequatorial Kelvin wave. Ray tracing analyses show that quasi-stationary Rossby waves with wavenumbers3, 4 and 5 explain part of the spatial structure of the circulation anomalies over the subtropical Americasrelated to the upward and downward vertical motions. The phase and amplitude of these waves depend onthe structure of the mean zonal flow and the location of the anomalous convective forcing, as concluded fromsensitivity experiments with a baroclinic model. An error in the simulated intensity of the mean zonal flow mayresult in phase shifts of the vertical motions and consequently, on errors in the simulated precipitationanomalies over the subtropical Americas. Some General Circulation Models, such as the NCAR CommunityClimate Model (CCM3) have this problem. Even more, a systematic bias is found in the CCM3, with weaker(stronger) than observed anomalies in extratropical (tropical) vertical motions, and consequently, in weaker(stronger) than observed precipitation anomalies. The implication of these analyses for seasonal climatepredictions at a regional level in the subtropical Americas is discussed. 2005 artículo científico 0187-6236 https://www.redalyc.org/articulo.oa?id=56518402 en http://www.redalyc.org/revista.oa?id=565 Atmósfera application/pdf Universidad Nacional Autónoma de México Atmósfera (México) Num.4 Vol.18
format	Artículo científico
id	redalyc_56518402
language	en
publishDate	2005
publisher	Universidad Nacional Autónoma de México
spellingShingle	Dynamics of subtropical vertical motions over the Americas during El Niño boreal winters V. Magaña Biología ENOS Rossby waves precipitation vertical motion Dynamics of subtropical vertical motions over the Americas during El Niño boreal winters V. Magaña T. Ambrizzi Biología ENOS Rossby waves precipitation vertical motion On the average, during boreal winter (December through February), the occurrence of El Niño/SouthernOscillation (ENSO) results in enhanced or diminished precipitation in various regions of the Americas.Anomalous convective activity in the central-eastern Pacific forces quasi-stationary Rossby waves thatfollow paths to the Northern and Southern hemispheres. The so-called Pacific-North American (PNA) patternresults in ascending motion and enhanced precipitation over California and the Gulf of Mexico. The PNA alsoaffects the Caribbean Sea by inhibiting winter tropical convection due to subsidence. In the SouthernHemisphere (SH), a weak quasi-stationary wave train is observed over southeast South America that resultsin enhanced ascending motion and precipitation. Over the equatorial region, the descending branch of astationary Kelvin wave inhibits convective activity over northeastern Brazil and other parts of northernSouth America. However, there are well known differences in the El Niño signal from one event to another inwhat is known as inter-ENSO variability. Through quasi-geostrophic analyses, the anomalous vertical motionsassociated with the quasi-stationary Rossby waves may be separated from those associated with the stationaryequatorial Kelvin wave. Ray tracing analyses show that quasi-stationary Rossby waves with wavenumbers3, 4 and 5 explain part of the spatial structure of the circulation anomalies over the subtropical Americasrelated to the upward and downward vertical motions. The phase and amplitude of these waves depend onthe structure of the mean zonal flow and the location of the anomalous convective forcing, as concluded fromsensitivity experiments with a baroclinic model. An error in the simulated intensity of the mean zonal flow mayresult in phase shifts of the vertical motions and consequently, on errors in the simulated precipitationanomalies over the subtropical Americas. Some General Circulation Models, such as the NCAR CommunityClimate Model (CCM3) have this problem. Even more, a systematic bias is found in the CCM3, with weaker(stronger) than observed anomalies in extratropical (tropical) vertical motions, and consequently, in weaker(stronger) than observed precipitation anomalies. The implication of these analyses for seasonal climatepredictions at a regional level in the subtropical Americas is discussed. 2005 artículo científico 0187-6236 https://www.redalyc.org/articulo.oa?id=56518402 en http://www.redalyc.org/revista.oa?id=565 Atmósfera application/pdf Universidad Nacional Autónoma de México Atmósfera (México) Num.4 Vol.18
title	Dynamics of subtropical vertical motions over the Americas during El Niño boreal winters
topic	Biología ENOS Rossby waves precipitation vertical motion
url	https://www.redalyc.org/articulo.oa?id=56518402

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