Atmospheric measurements of the Atlantic ITCZ during a ship campaign in summer 2021

The intertropical convergence zone (ITCZ) plays a central role for the tropical weather and climate and structures the large-scale circulation. As a result, the ITCZ has long been an intensively studied research topic, with most studies of the ITCZ focusing on its long-term and large-scale characteristics. However, recent modeling results have highlighted the role of storm-scale processes in the formation of the ITCZ, suggesting that our limited ability to represent these small-scale processes correctly may contribute to persistent errors in the representation of the ITCZ in climate models. Looking at the ITCZ on short spatial and temporal scales, even the question of where the low-level convergence in the ITCZ occurs appears to be unclear. Do the trade winds from the north and south meet in a narrow line of convergence, or are there two lines of convergence marking the northern and southern edges of the ITCZ? To answer this question, we performed measurements on board the German research vessel Sonne during the campaign "Mooring Rescue" in the tropical Atlantic in summer 2021. During the campaign, the thermodynamic and dynamical state of the atmosphere was measured by frequent radiosonde launches, which provided atmospheric profiles with high vertical resolution extending from the surface to the lower stratosphere. These measurements were supplemented by continuous measurements of the atmospheric boundary layer and lower free troposphere, including optical measurements of water vapor, aerosol, precipitation, wind speed and direction, and cloud base height. Here, we provide a brief overview of the atmospheric measurements and a preliminary assessment of the dynamic state observed during a north-south crossing of the ITCZ. The ship-based measurements were compared with long-term statistics from reanalysis data and satellite observations.