Aerosol partitioning in natural mixed‐phase clouds

Abstract

In situ aerosol and cloud drop microphysical measurements at a high‐alpine site are used to investigate aerosol partitioning between cloud and interstitial phases in natural, mid‐latitude, mixed‐phase clouds. Measurements indicate a decrease in the activated aerosol fraction ( F N ) for particle diameters d P > 100 nm with cloud temperature from F N ∼ 0.54 in summer liquid‐phase clouds to F N ∼ 0.08 in winter mixed‐phase clouds. The latter may be attributed to the Bergeron‐Findeisen mechanism whereby ice crystals grow at the expense of liquid water drops, releasing formerly activated aerosols back into the interstitial phase. This provides a means to distinguish the indirect effects of aerosols on drops and ice crystals.