Dynamical Controls on Interannual ITCZ Variability over the Indian Summer Monsoon Domain

Abstract. The Intertropical Convergence Zone (ITCZ) is a narrow band of intense convection formed by the convergence of tropical trade winds, leading to intense convection and precipitation. Its seasonal and interannual variations have significant socio-economic impacts, particularly over the Indian subcontinent, where the shifts in ITCZ position influence monsoon rainfall. Using long-term precipitation and atmospheric reanalysis data, this study investigates the interannual variability of boreal summer ITCZ latitudes, quantified using multivariate probabilistic approach, over the Indian region and its associated circulation changes. Extreme northward ITCZ shift years are associated with enhanced convection, strengthened monsoon westerlies, and intensified ascent leading to increased precipitation over the monsoon core zone along with poleward-displaced regional Hadley circulation, while extreme southward shift exhibits opposite features. Large-scale climate modes such as the El Niño–Southern Oscillation modulate tropical heating and circulation, influencing ITCZ position. Additionally, a significant long-term northward shift of the ITCZ during 1940–2022 is identified, which is closely linked to changes in moist static energy transport. A corresponding poleward shift of the meridional energy transport indicates that this migration is driven by changes in atmospheric energy balance.