Bimodal CCN Spectra

For original submission and image(s), see ARM Research Highlights http://www.arm.gov/science/highlights/ Research Highlight Aerosol spectra under marine stratus are often bimodal and attributable to cloud processes. Sizes at the minima between the modes have inferred supersaturations (S) of nearby clouds (Hoppel et al. 1985, 1994). This was based on the principle that the lower critical S (Sc) particles that produced cloud droplets were increased by 1) chemical reactions within droplets, and 2) Bownian capture of interstitial particles and coalescence among droplets. Thus, upon evaporation, the dry particles had even lower Sc. This resulted in a size/Sc gap because the higher Sc particles that did not form droplets were unchanged.