Validation of satellite-retrieved CCN based on a cruise campaign over the polluted Northwestern Pacific ocean

In this study, we present and validate a methodology for satellite retrievals of cloud condensation nuclei (CCN) in shallow marine boundary layer clouds. In our approach, supersaturation (S) is calculated by the retrieved cloud base drop concentration (Nd) and updrafts (Wb). Nd is the activated CCN concentration in clouds at a given S. We validate the accuracy of the satellite retrieval against surface-measured CCNs from a cruise campaign over the heavily polluted northwest Pacific Ocean. The satellite retrievals show a good agreement with surface measurements after performing corrections for temperature and adiabatic fraction when clouds are coupled with sea surface. This study broadens the applicability of the methodology from aerosol-limited to contaminated regions. The validation shows +/- 30% accuracy in retrieving CCN over both clean and polluted regions. The results further demonstrate the strong dependence of marine shallow cloud Nd on CCN number concentrations and updraft, which allows us to further apply this methodology to quantify CCN, cloud microphysical properties and the relationships between them. This is helpful in reducing the uncertainty of radiation forcing caused by the aerosolcloud-interactions (ACI).

Automated summary

This study introduces and validates a methodology for satellite retrievals of cloud condensation nuclei in shallow marine boundary layer clouds, demonstrating good accuracy in both clean and polluted regions. By comparing satellite retrievals with surface-measured CCNs, this methodology shows potential in quantifying CCN, cloud microphysical properties, and their relationships, which is beneficial for reducing the uncertainty of radiation forcing from aerosol-cloud interactions.