The intertropical convergence zone (ITCZ) is like a heartbeat to Earth’s climate system, serving as the Hadley circulation’s rising branch and producing some of the most intense rainfall. Textbook descriptions show that the ITCZ follows the Sun’s seasonal migration. However, such definitions are deficient for the east Pacific Ocean ITCZ, which is centered north of the equator except during boreal spring when a double ITCZ forms. For decades, climate models have been overproducing the double ITCZ such that the double ITCZ becomes the dominant ITCZ state half of the year, or for some models, the secondary ITCZ dominates.
In this talk, I place focus on recently documented observed daily-weekly east Pacific ITCZ shifts to tackle the problem of climate model double ITCZ biases. During boreal spring, the climatological equatorial meridional surface winds dip down near zero in conjunction with the climatological double ITCZ during spring so that any significant meridional wind variability alters the interhemispheric transport of moisture, energy, momentum, and thus, ITCZ position. There are several distinct dynamical features that appear in the days leading up to the two leading types of ITCZ events, nITCZ (Northern Hemisphere) and dITCZ (double). Southerly and northerly equatorial flows intensify over a zonally wide east Pacific region preceding nITCZ and dITCZ events, respectively. A meridional momentum budget analysis reveals that both linear and nonlinear dynamics are important to the intensification of cross-equatorial flow associated with nITCZ and dITCZ events. Additionally, I show a potential role for extratropical teleconnections in both nITCZ and dITCZ events.