Droplet Spectra Broadening by Ripening Process. Part I: Roles of Curvature and Salinity of Cloud Droplets

The “ripening process” occurs due to thermodynamic instability of droplet size spectra in clouds. This instability results from the existence of droplets with different salinity and size in the droplet spectra. The ripening process is independent of turbulent fluctuations of supersaturation for a closed cloud parcel. Because of the ripening process, droplet number concentration continuously decreases with time after the initial peak supersaturation, which occurs during the initial updraft. Droplet spectra broaden to large sizes by evaporation of small droplets. Both mean droplet size and the standard deviation of droplet size spectra increase with time. This mechanism is suggested to be a potential physical mechanism for the formation of droplet size spectra in stratiform clouds.