CCN and cloud droplet concentrations at a remote ocean site

Extensive aircraft measurements over the mid Pacific displayed unexpectedly high overall average concentrations of condensation nuclei (CN) of 379 cm−3, cloud condensation nuclei (CCN) at 1% supersaturation (NCCN) of 301 cm−3, and total cloud droplets (Nc) of 139 cm−3. Factor of two variations in average NCCN and Nc among 11 flights produced a positive correlation coefficient (R) of 0.81. Updraft velocity (W) was also positively correlated with Nc but with lower R. Comparisons with a more traditionally maritime project (RICO), which had higher average W clearly demonstrated the role of W in determining Nc. Correlations of NCCN with concentrations of larger droplets were negative but the R switched back to positive for concentrations of largest cloud droplets with NCCN. The explanation offered for this double reversal of R for NCCN with droplet concentrations greater than various sizes suggests yet another influence of the aerosol on cloud microphysics.