The quantification of large-scale cloud radiative effects across the Atlantic ITCZ

The clouds of the Intertropical Convergence Zone (ITCZ), particularly deep convective clouds, play a pivotal role in the atmospheric circulation of energy and moisture as well as associated feedback processes. The Persistent EarthCARE underflight studies of the ITCZ and organized convection (PERCUSION) airborne campaign in 2024 sought to investigate the organization of convection in the ITCZ region across the Atlantic Ocean. The flight strategy of PERCUSION enabled the characterization of the cloud field across the northern and southern boundaries of the ITCZ as well as the eastern and western ends of the Atlantic basin, each of which is distinct in its aerosol and dynamic conditions.

The asymmetric and dynamic structure of the ITCZ implies differences in cloudiness and cloud properties at the northern and southern boundaries of the ITCZ. To assess the impacts that these differences have on the radiative energy budget of the Tropics, we provide a statistical characterization of the radiative effects (CRE) of these clouds. Airborne irradiance observations at flight altitude from the Broadband AirCrAft RaDiometer Instrumentation (BACARDI) on the research aircraft HALO are used to calculate the CRE, which is separated into its solar and thermal infrared components. To assess the representativeness of the airborne observations, satellite observations (e.g. GOES, EarthCARE) and reanalysis data from the same period and beyond will be used.

Additionally, the synergy of these datasets allows for the characterization of the CRE drivers, e.g. macro- or microphysical cloud properties. Observations during the 2020 Elucidating the Role of Cloud-Circulation Coupling and Climate (EUREC⁴A) campaign already demonstrated that the macrophysical properties of shallow cumulus clouds were the main driver of the solar and thermal-infrared CRE when cloud fractions were low, while microphysical properties became more relevant at higher cloud fractions. The PERCUSION campaign provides the opportunity to extend these results to deeper convection and more complex cloud systems.