Correlations of CCN Concentrations With Small Cumuli Droplet and Drizzle Drop Concentrations

Aircraft field measurements of cloud condensation nuclei (CCN) and cloud microphysics in maritime air masses during the RICO project, December-January, 2004-05 showed ubiquitous influence of CCN. Flight averages of CCN concentrations and cloud droplet and drizzle drop concentrations were examined for as many as 17 flights. CCN concentrations at only one supersaturation (S) of 1% measured at 100m altitude were compared with cloud droplet and drizzle drop concentrations at six altitude ranges between 600 and 3000m. Consistently high positive correlations (R) were found with total and small cumulative cloud droplet concentrations over all altitudes. These high R values also persisted for cloud parcels with a wide range of liquid water contents (LWC) most of which were far below adiabatic (unmixed) values. For all but the lowest LWC parcels, R was essentially constant. There was an even more consistent negative R between CCN and large cloud droplet and drizzle drop concentrations. There was a consistently sharp droplet size transition from large positive R to just as large negative R that increased with altitude and LWC. Entrainment did show an opposite effect on R but this was only apparent at the highest altitudes where entrainment was greatest and only for the smallest droplet sizes. These results indicate that the effect of CCN concentrations on cloud microphysics was pervasive with altitude, LWC, cloud droplet and drizzle drop concentrations. This indicates greater impact of the indirect aerosol effect (IAE) in both of its manifestations; First IAE (cloud radiation), and Second IAE (precipitation).