Marine stratocumulus aerosol‐cloud relationships in the MASE‐II experiment: Precipitation susceptibility in eastern Pacific marine stratocumulus

Observational data on aerosol‐cloud‐drizzle relationships in marine stratocumulus are presented from the second Marine Stratus/Stratocumulus Experiment (MASE‐II) carried out in July 2007 over the eastern Pacific near Monterey, California. Observations, carried out in regions of essentially uniform meteorology with localized aerosol enhancements due to ship exhaust (“ship tracks”), demonstrate, in accord with those from numerous other field campaigns, that increased cloud drop number concentration N c and decreased cloud top effective radius r e are associated with increased subcloud aerosol concentration. Modulation of drizzle by variations in aerosol levels is clearly evident. Variations of cloud base drizzle rate R cb are found to be consistent with the proportionality, R cb ∝ H 3 / N c , where H is cloud depth. Simultaneous aircraft and A‐Train satellite observations are used to quantify the precipitation susceptibility of clouds to aerosol perturbations in the eastern Pacific region.