Observations and Reconstruction Methods of Cloud Condensation Nuclei, Cloud Droplet Number and Their Atmospheric Drivers during CAMP2Ex in the Western Pacific

As part of the NASA CAMP2Ex field campaign, we observed cloud condensation nuclei (CCN) spectra between 0.1 and 0.6% supersaturation onboard the NASA P-3B research aircraft during seven research flights over the Pacific Ocean originating from Clark Freeport in the Philippines. The CCN spectra were measured with a Droplet Measurement Technologies CCN-100 continuous-flow streamwise thermal gradient chamber (CFSTGC) operating in both constant flow and Scanning Flow CCN Analysis mode. Combination of the CCN spectra and submicron aerosol size distributions (10 600 nm) from the Fast Integrated Mobility Spectrometer (FIMS) are used to obtain size-resolved CCN hygroscopicity - which are compared with submicron aerosol hygroscopicity obtained from with Aerosol Mass Spectrometer (AMS) data. During periods of high sulfate fraction, the CCN data are used to calibrate the instrument supersaturation levels. The vertical velocity distribution is determined for each flight leg in the planetary boundary layer. The hygroscopicity and aerosol observations, together with the updraft velocity distributions, are used as inputs to the cloud droplet activation parameterization of Morales and Nenes1 to determine the level of cloud droplets and supersaturation that would occur in non-precipitating clouds. From these outputs we also determine the degree to which clouds respond to aerosol perturbations, and quantitatively determine the contribution of aerosol and vertical velocity variability to the droplet number variability. Periods in which droplet formation is controlled by aerosol concentration or vertical updraft velocity are examined based on their geographic location over land or over water using meteorological and aerosol measurements in combination with flight data including video files. Finally, we relate our results to a growing body of studies focused on the drivers of droplet variability in the eastern Mediterranean, South Atlantic Ocean and southeastern United States.2-4 Morales Betancourt, R.; Nenes, A., Geosci. Model Dev. 2014, 7 (5), 2345-2357 Bougiatioti, A.; Nenes, A.; et al., Atmos. Chem. Phys. 2020, 20 (20), 12163-12176 Kacarab, M.; Thornhill, K. L.; et al., Atmos. Chem. Phys. 2020, 20 (5), 3029-3040 Kalkavouras, P.; Bougiatioti, A.; et al., Atmos. Chem. Phys. 2019, 19 (9), 6185-6203