The inner life of the Atlantic Intertropical Convergence Zone

The Intertropical Convergence Zone (ITCZ) is a central component of the atmospheric general circulation, but remarkably little is known about the dynamical and thermodynamical structure of the convergence zone itself. This is true even for the structure of the low-level convergence that gives the ITCZ its name. Following on from the major international field campaigns in the 1960s and 1970s, we performed extensive atmospheric profiling of the Atlantic ITCZ during a ship-based measurement campaign aboard the research vessel SONNE in summer 2021. Combining data collected during our north-south crossing of the ITCZ with reanalysis data shows the ITCZ to be a meridionally extended region of intense precipitation, with enhanced surface convergence at its edges rather than in the center. Based on the location of these edges, we construct a composite view of the structure of the Atlantic ITCZ. The ITCZ, far from being simply a region of enhanced deep convection, has a rich inner life, that is, a rich dynamical and thermodynamic structure that changes throughout the course of the year, and has a northern edge that differs systematically from the southern edge. The Atlantic Intertropical Convergence Zone (ITCZ) has a rich inner life that is immediately apparent from satellite imagery, such as shown here (Suomi NPP / VIIRS from NASA Worldview for the 10th of July 2021, ). In this study, we peer into this inner life by combining observational data collected during a north-south crossing of the East Atlantic ITCZ in summer with multiyear reanalysis data. Most of the time, the Atlantic ITCZ is best described as a meridionally extended region of intense precipitation, with enhanced surface convergence at its edges rather than in the center.image