Open AccessA Multiscale Model for the Modulation and Rectification of the ITCZ
Author(s) -
Joseph A. Biello,
Andrew J. Majda
Publication year - 2013
Publication title -
journal of the atmospheric sciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.853
H-Index - 173
eISSN - 1520-0469
pISSN - 0022-4928
DOI - 10.1175/jas-d-12-0142.1
Subject(s) - intertropical convergence zone , mesoscale meteorology , rossby wave , convection , equator , geology , hadley cell , gravity wave , climatology , atmospheric sciences , troposphere , kelvin wave , breaking wave , geophysics , meteorology , physics , wave propagation , gravitational wave , geodesy , general circulation model , climate change , latitude , astrophysics , precipitation , oceanography , quantum mechanics
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 are modulated by a large-scale gravity wave that is also generated by convection. Westward-propagating disturbances are observed to cause ITCZ breakup over the course of a few days, and the M-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 eastward-propagating 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.