The role of vertical shear of the meridional winds in the northward propagation of ITCZ

Abstract

A simple linear model was proposed by Jiang et al. (2004) to highlight the mechanism of scale selection during the northward propagation of cloud bands over Bay of Bengal. The easterly shear in zonal winds was shown to be an essential parameter in scale selection. This model was criticized for the use of unrealistic values of the friction and diffusion parameters. The present study extends this model by adding baroclinic vertical shear in the meridional mean winds. The correct rate of propagation is obtained with reasonable values of friction and diffusion parameters. In the present model, the direction of propagation is essentially determined by easterly vertical shear of zonal winds, while vertical shear of meridional wind also contributes to the observed propagation phase speed and instability. The correct phase speed is obtained for southerly mean meridional vertical shear.