ITCZ breakdown and its upscale impact on the planetary-scale circulation over the eastern Pacific

Qiu Yang, Andrew J. Majda, Boualem Khouider

Research output: Contribution to journalArticle

Abstract

The eastern Pacific (EP) intertropical convergence zone (ITCZ) is sometimes observed to break down into several vortices on the synoptic time scale. It is still a challenge for present-day numerical models to simulate the ITCZ breakdown in the baroclinic modes. Also, the upscale impact of the associated mesoscale fluctuations on the planetary-scale circulation is not well understood. Here, a simplified multiscale model for the modulation of the ITCZ is used to study these issues. A prescribed two-scale heating drives the planetary-scale circulation through both planetary-scale mean heating and eddy flux divergence of zonal momentum, where the latter represents the upscale impact of mesoscale disturbances. In an idealized scenario where the heating only varies on the mesoscale, key features of the ITCZ breakdown in the baroclinic modes are captured. The eddy flux divergence of zonal momentum is characterized by midlevel (low level) eastward (westward) momentum forcing at subtropical latitudes of the Northern Hemisphere and opposite-signed midlevel momentum forcing at low latitudes. Such upscale impact of mesoscale fluctuations tends to accelerate (decelerate) planetary-scale zonal jets in the middle (lower) troposphere. Compared with deep heating, shallow heating induces stronger vorticity anomalies on the mesoscale and more significant eddy flux divergence of zonal momentum and acceleration-deceleration effects on the planetary-scale mean flow. In a more realistic scenario where the heating also varies on the planetary scale, the most significant zonal velocity anomalies are confined in the diabatic heating region.

Original languageEnglish (US)
Pages (from-to)4023-4045
Number of pages23
JournalJournal of the Atmospheric Sciences
Volume74
Issue number12
DOIs
StatePublished - Dec 1 2017

Fingerprint

intertropical convergence zone
heating
momentum
baroclinic mode
eddy
divergence
anomaly
vorticity
vortex
troposphere
Northern Hemisphere
timescale
disturbance

Keywords

  • Atmospheric circulation
  • Baroclinic flows
  • Deep convection
  • Intertropical convergence zone
  • Meridional overturning circulation
  • Numerical analysis/modeling

ASJC Scopus subject areas

  • Atmospheric Science

Cite this

ITCZ breakdown and its upscale impact on the planetary-scale circulation over the eastern Pacific. / Yang, Qiu; Majda, Andrew J.; Khouider, Boualem.

In: Journal of the Atmospheric Sciences, Vol. 74, No. 12, 01.12.2017, p. 4023-4045.

Research output: Contribution to journalArticle

Yang, Qiu ; Majda, Andrew J. ; Khouider, Boualem. / ITCZ breakdown and its upscale impact on the planetary-scale circulation over the eastern Pacific. In: Journal of the Atmospheric Sciences. 2017 ; Vol. 74, No. 12. pp. 4023-4045.
@article{4ea629d84ad0498b88dd9a2819ab063d,
title = "ITCZ breakdown and its upscale impact on the planetary-scale circulation over the eastern Pacific",
abstract = "The eastern Pacific (EP) intertropical convergence zone (ITCZ) is sometimes observed to break down into several vortices on the synoptic time scale. It is still a challenge for present-day numerical models to simulate the ITCZ breakdown in the baroclinic modes. Also, the upscale impact of the associated mesoscale fluctuations on the planetary-scale circulation is not well understood. Here, a simplified multiscale model for the modulation of the ITCZ is used to study these issues. A prescribed two-scale heating drives the planetary-scale circulation through both planetary-scale mean heating and eddy flux divergence of zonal momentum, where the latter represents the upscale impact of mesoscale disturbances. In an idealized scenario where the heating only varies on the mesoscale, key features of the ITCZ breakdown in the baroclinic modes are captured. The eddy flux divergence of zonal momentum is characterized by midlevel (low level) eastward (westward) momentum forcing at subtropical latitudes of the Northern Hemisphere and opposite-signed midlevel momentum forcing at low latitudes. Such upscale impact of mesoscale fluctuations tends to accelerate (decelerate) planetary-scale zonal jets in the middle (lower) troposphere. Compared with deep heating, shallow heating induces stronger vorticity anomalies on the mesoscale and more significant eddy flux divergence of zonal momentum and acceleration-deceleration effects on the planetary-scale mean flow. In a more realistic scenario where the heating also varies on the planetary scale, the most significant zonal velocity anomalies are confined in the diabatic heating region.",
keywords = "Atmospheric circulation, Baroclinic flows, Deep convection, Intertropical convergence zone, Meridional overturning circulation, Numerical analysis/modeling",
author = "Qiu Yang and Majda, {Andrew J.} and Boualem Khouider",
year = "2017",
month = "12",
day = "1",
doi = "10.1175/JAS-D-17-0021.1",
language = "English (US)",
volume = "74",
pages = "4023--4045",
journal = "Journals of the Atmospheric Sciences",
issn = "0022-4928",
publisher = "American Meteorological Society",
number = "12",

}

TY - JOUR

T1 - ITCZ breakdown and its upscale impact on the planetary-scale circulation over the eastern Pacific

AU - Yang, Qiu

AU - Majda, Andrew J.

AU - Khouider, Boualem

PY - 2017/12/1

Y1 - 2017/12/1

N2 - The eastern Pacific (EP) intertropical convergence zone (ITCZ) is sometimes observed to break down into several vortices on the synoptic time scale. It is still a challenge for present-day numerical models to simulate the ITCZ breakdown in the baroclinic modes. Also, the upscale impact of the associated mesoscale fluctuations on the planetary-scale circulation is not well understood. Here, a simplified multiscale model for the modulation of the ITCZ is used to study these issues. A prescribed two-scale heating drives the planetary-scale circulation through both planetary-scale mean heating and eddy flux divergence of zonal momentum, where the latter represents the upscale impact of mesoscale disturbances. In an idealized scenario where the heating only varies on the mesoscale, key features of the ITCZ breakdown in the baroclinic modes are captured. The eddy flux divergence of zonal momentum is characterized by midlevel (low level) eastward (westward) momentum forcing at subtropical latitudes of the Northern Hemisphere and opposite-signed midlevel momentum forcing at low latitudes. Such upscale impact of mesoscale fluctuations tends to accelerate (decelerate) planetary-scale zonal jets in the middle (lower) troposphere. Compared with deep heating, shallow heating induces stronger vorticity anomalies on the mesoscale and more significant eddy flux divergence of zonal momentum and acceleration-deceleration effects on the planetary-scale mean flow. In a more realistic scenario where the heating also varies on the planetary scale, the most significant zonal velocity anomalies are confined in the diabatic heating region.

AB - The eastern Pacific (EP) intertropical convergence zone (ITCZ) is sometimes observed to break down into several vortices on the synoptic time scale. It is still a challenge for present-day numerical models to simulate the ITCZ breakdown in the baroclinic modes. Also, the upscale impact of the associated mesoscale fluctuations on the planetary-scale circulation is not well understood. Here, a simplified multiscale model for the modulation of the ITCZ is used to study these issues. A prescribed two-scale heating drives the planetary-scale circulation through both planetary-scale mean heating and eddy flux divergence of zonal momentum, where the latter represents the upscale impact of mesoscale disturbances. In an idealized scenario where the heating only varies on the mesoscale, key features of the ITCZ breakdown in the baroclinic modes are captured. The eddy flux divergence of zonal momentum is characterized by midlevel (low level) eastward (westward) momentum forcing at subtropical latitudes of the Northern Hemisphere and opposite-signed midlevel momentum forcing at low latitudes. Such upscale impact of mesoscale fluctuations tends to accelerate (decelerate) planetary-scale zonal jets in the middle (lower) troposphere. Compared with deep heating, shallow heating induces stronger vorticity anomalies on the mesoscale and more significant eddy flux divergence of zonal momentum and acceleration-deceleration effects on the planetary-scale mean flow. In a more realistic scenario where the heating also varies on the planetary scale, the most significant zonal velocity anomalies are confined in the diabatic heating region.

KW - Atmospheric circulation

KW - Baroclinic flows

KW - Deep convection

KW - Intertropical convergence zone

KW - Meridional overturning circulation

KW - Numerical analysis/modeling

UR - http://www.scopus.com/inward/record.url?scp=85040348621&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85040348621&partnerID=8YFLogxK

U2 - 10.1175/JAS-D-17-0021.1

DO - 10.1175/JAS-D-17-0021.1

M3 - Article

VL - 74

SP - 4023

EP - 4045

JO - Journals of the Atmospheric Sciences

JF - Journals of the Atmospheric Sciences

SN - 0022-4928

IS - 12

ER -