Effect of Aerosol on the Susceptibility and Efficiency of Precipitation in Warm Trade Cumulus Clouds

Large eddy simulations of warm trade wind cumulus clouds are conducted for a range of aerosol conditions with a focus on precipitating clouds Individual clouds are tracked over the course of their lifetimes Precipitation rate decreases progressively as aerosol Increases For larger precipitating clouds the polluted clouds have longer lifetimes because of precipitation suppression For clean aerosol conditions there is good agreement between the average model precipitation rate and that calculated based on observed radar reflectivity Z and precipitation rate R relationships Precipitation rate can be expressed as a power law function of liquid water path (LWP) and N-d to reasonable accuracy The respective powers for LWP and N-d are of similar magnitude compared to those based on observational studies of stratocumulus clouds The time integrated precipitation rate represented by a power law function of LWP N-d and cloud lifetime is much more reliably predicted than is R expressed in terms of LWP and N-d alone The precipitation susceptibility (So = dInR/dInN(d)) that quantifies the sensitivity of precipitation to changes in N-d depends strongly on LWP and exhibits nonmonotonic behavior with a maximum at intermediate LWP values The relationship between So and precipitation efficiency is explored and the Importance of including dependence on N-d in the latter is highlighted The results provide trade cumulus cloud population statistics as well as relationships between (memicrophysical/macrophysical properties and precipitation that are amenable for use in larger scale models