Helicopter-borne measurements of small-scale processes in shallow cumulus convection over Barbados

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The project proposed here aims at examining the complex interactions between atmospheric aerosol particles, small scale cloud dynamics, particle number size distributions, and radiative properties of trade wind cumulus clouds. The helicopter borne platform ’ACTOS’ will be used to measure meteorological parameters and properties of aerosol and clouds at Barbados. Measurements will be done in- and outside of clouds, with a high spatial resolution. For the first time, ACTOS will carry an adapted small CCNc (Cloud Condensation Nuclei counter) and newly developed fast instrumentation for aerosol characterization. Compared to aircraft measurements, the high spatial and temporal resolution, together with the low speed at which a helicopter flies, will enable a detailed examination of individual small trade wind cumuli and of their entrainment regions. Due to the ongoing mixing in these regions, they are important for the development of the cloud (droplet size distribution) as well as for modifying the aerosol (cloud processing, e.g. a change in particle hygroscopicity). This then also influences the optical properties of the cloud and its surroundings, and to capture this, radiation measurements will be done with instruments being positioned beneath the helicopter. By combining the different aspects, and particularly by examining the influence of different atmospheric aerosols, we aim at obtaining a better description of the early stages of trade wind cumuli, enabling a more detailed description of this cloud type in numerical (climate-) models. These proposed activities are embedded into a long term measurement program that will last for two years and that is realized by the MPI Hamburg (including remote sensing and measurements on the HALO aircraft).