First insights into the diverse remote sensing observations of convection during BOW-TIE

Convection, which influences cloud and precipitation properties as well as, the radiative effects of clouds, needs to be better understood for a comprehensive picture of interconnected climate processes all over the globe and requires a better representation for accurate climate projections. Meanwhile, the modelling of these phenomena is already a challenge itself, the quality and quantity of high-resolution observational data of convective clouds are limited, especially over the (tropical) oceans. The recent measurement campaign BOW-TIE (“Beobachtung von Ozean und Wolken – das Trans ITCZ Experiment”) on board the research vessel Meteor in August and September 2024 focussed on atmospheric and oceanic measurements inside the Atlantic ITCZ (intertropical convergence zone), between Mindelo (Cabo Verde) and Bridgetown (Barbados). Our working group from the Leipzig Institute for Meteorology concentrated on the investigation of the microphysical properties of clouds and precipitation by deploying a continuously measuring remote sensing suite mainly consisting of a motion-stabilized, vertically-pointing 94 GHz cloud radar and a microwave radiometer (MWR; to derive liquid water path (LWP) and integrated water vapor (IWV)) on the research vessel. In combination with data obtained with the ceilometer deployed by the MPI for Meteorology Hamburg, the synergetic Cloudnet processing chain can be employed. Cloudnet products include a hydrometeor target classification as well as cloud microphysical properties like the effective radius of cloud droplets and ice crystals, the hydrometeors phase, ice water content (IWC), and liquid water content (LWC). All observed and derived cloud and precipitation characteristics are contrasted between the Eastern and Western Atlantic. A first insight reveals the dominance of shallow convective clouds in the Eastern Atlantic, while the Western Atlantic also evinces convective clouds with a height up to six kilometers and cirrus clouds more frequently. Related to the frequency of occurrence of the different cumulus cloud types, the distribution of the microphysical properties like the effective radius of hydrometeors, IWC, and LWC allows for a more detailed glimpse into differences of the processes in the Eastern and Western ITCZ. With that, the convective processes above the tropical Atlantic Ocean are studied concerning microphysics and their distribution and contribute to an improved understanding of cloud-affecting processes.