Precipitation susceptibility in marine stratocumulus and shallow cumulus clouds

In this study we explored the precipitation susceptibility (S0) by using in situ observations obtained from four field campaigns--two focusing on marine stratocumulus clouds and two focusing on cumulus clouds. For the stratocumulus cloud campaigns, 13-flights during the VOCALS (VAMOS Ocean-Cloud-Atmosphere-Land Study, 2007) and 12-flights during the EPEACE (Eastern Pacific Emitted Aerosol-Cloud Experiment, 2011) data were processed. Data obtained from 10 flights from BACEX (Barbados Aerosol Cloud Experiment, 2010) and 4 flights from KWACEX (Key West Aerosol Cloud Experiment, 2012) are processed for the estimation of S0 for shallow marine cumulus clouds. The CIRPAS Twin Otter research aircraft served as the principal platform from which observations were made. It was equipped with an extensive suite of instrumentation for characterizing clouds and aerosols. In addition, an FMCW Doppler 94 GHz cloud radar was mounted on top of the aircraft in an upward facing mode and provided cloud and precipitation structures above the aircraft. Cloud top heights were determined from the cloud radar reflectivity and cloud droplet number concentrations and precipitation were calculated from the drop size distribution obtained during observations made near cloud base. This study shows consistent behaviors of S0 regardless of the cloud types; i.e. susceptibility increases with cloud thickness and peaks at intermediate cloud depths, then decreases again for higher cloud depths in both stratocumulus and cumulus clouds. We will compare and discuss our results with those from past studies in warm cumulus and stratocumulus clouds. In addition, we will discuss the effects of giant cloud condensation nuclei introduced artificially into the stratocumulus clouds on precipitation effects and susceptibility.