Evidence for accretional drop growth in shallow tropical convection based on four-dimensional dual Doppler radar data

The range of conditions under which drops could grow by accretion of cloud water from ultragiant CCN to observed 4-8 mm diameters is determined during a simple up-down trajectory through shallow Hawaiian clouds. A Lagrangian drop-growth trajectory model applied within dual-Doppler four-dimensional kinematic fields collected on the Hawaiian Rainband Project. The fields provided realistic time scales and magnitudes of convective updrafts, and also considered the horizontal flow variations that can transport drops into and out of updrafts. Sensitivity studies for the August 1990 case showed that it is possible for raindrops to grow large on ultragiant nuclei by accretion of cloud water alone during a single up-down trajectory.