An airborne study of the aerosol effect on the dispersion of cloud droplets in a drizzling marine stratocumulus cloud over eastern China111

Detailed airborne measurements were carried out to explore aerosol-cloud interactions and cloud microphysical properties in a drizzling marine stratocumulus cloud deck over eastern China. Results show that the collision coalescence of cloud droplets, the condensation of small droplets, and the collision-induced break-up of drizzle were the dominant microphysical processes in the sampled water cloud parcel. The region in the vicinity of the cloud's lateral boundary was spatially divided into sub-regions to better understand aerosol and droplet interactions. Relationships between the relative dispersion (epsilon) and the cloud''s microphysical and dynamical characteristics were also examined. A negative relation was found between epsilon and the cloud droplet number concentration, with epsilon showing a close relationship with the liquid water content (LWC) and updraft velocity. When LWC was greater than similar to 0.75 g kg(-1), the range of epsilon values narrowed, and updrafts dominated. By introducing epsilon in the cloud droplet effect radius (R-e) parameterization, we find that epsilon can further affect indirect forcing by changing the Re distribution for the cloud examined in this study. The dispersion effect (DE) was estimated using the effective radius ratio and the specific cloud water content. An in-depth analysis indicates that DE may offset the Twomey effect by similar to 12%. Two different methods of estimating the indirect effect (IE) yielded close values (0.084 and 0.077), suggesting that introducing DE into the estimation had a small influence on the IE calculation in the drizzling marine stratocumulus cloud of this study. Note that the estimated IE has a large uncertainty, given the large biases in the cloud properties measured.

Automated summary

Detailed airborne measurements were conducted in a drizzling marine stratocumulus cloud deck over eastern China to investigate aerosol-cloud interactions and cloud microphysical properties. The findings revealed that collision coalescence of cloud droplets, condensation of small droplets, and collision-induced break-up of drizzle were the dominant microphysical processes in the sampled water cloud parcel. Additionally, a negative relationship between relative dispersion (epsilon) and cloud droplet number concentration was observed, with epsilon closely related to liquid water content (LWC) and updraft velocity.