Role of changing CCN concentrations in precipitation formation using a parcel and a trajectory model in four-dimensional Doppler radar fields

A study was conducted to test the hypothesis that total cloud condensation nuclei (CCN) concentrations play little role in determining the timing of the onset of precipitation in clouds with similar updraft and liquid water content characteristics, provided that giant and ultragiant particles are present near cloud base in sufficient concentrations. The hypothesis was tested using a drop growth trajectory model and a moment-conserving parcel model. Model calculations support the tested hypothesis.