A multiscale model for the modulation and rectification of the ITCZ

Joseph A. Biello, Andrew J. Majda

Research output: Contribution to journalArticlepeer-review


The authors introduce the modulation of the ITCZ equations (M-ITCZ), which describes the multiscale dynamics of the ITCZ on diurnal to monthly time scales in which mesoscale convectively coupled Rossby waves in the ITCZ aremodulated by a large-scale gravity wave that is also generated by convection.Westwardpropagating disturbances are observed to cause ITCZ breakup over the course of a few days, and theM-ITCZ meso-/planetary-scale coupled waves provide a mechanism for this interaction, thereby providing a framework to study the modulation and rectification of the Hadley circulation over long zonal length scales in the ITCZ. The authors consider examples of zonally symmetric heating profiles in the M-ITCZ system and generate a Hadley circulation consistent with the observed winds. Zonally localized heating creates a wind response throughout the tropics that is carried by a pair of zonally propagating gravity bores driving mean easterlies at the base and mean westerlies at the top of the troposphere. The bores carry low-temperature and upward velocity perturbations to the west of the heating and high-temperature and downward velocity perturbations to the east, making the westward-propagating branch favorable to convective triggering and the eastwardpropagating branch favorable to convective suppression. The mesoscale dynamics of the M-ITCZ describe convectively forced, nonlinear Rossby waves propagating in the zonal winds created by the planetary-scale gravity wave. The authors suggest that convective coupling slows the westward-propagating gravity wave, thereby creating a coupled gravity-Rossby wave that is similar to the westward-propagating disturbances seen in the ITCZ.

Original languageEnglish (US)
Pages (from-to)1053-1070
Number of pages18
JournalJournal of the Atmospheric Sciences
Issue number4
StatePublished - Apr 2013


  • Atmospheric
  • Dynamics
  • Hadley circulation
  • Mesoscale systems
  • Nonlinear models
  • Walker circulation
  • Waves

ASJC Scopus subject areas

  • Atmospheric Science


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