The inner life of the Atlantic ITCZ

The intertropical convergence zone (ITCZ) is a central component of the global circulation system, 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 70s, we performed extensive atmospheric profiling of the Atlantic ITCZ during a ship-based measurement campaign aboard the research vessel SONNE in summer 2021. Combining the data we collected during our north-south crossing of the ITCZ with reanalysis data shows that there are generally two low-level convergence lines that roughly mark the southern and northern edges of the region of intense precipitation. Based on the location of these two 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, i.e., 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.