Precipitation efficiency of trade wind clouds over the north central tropical Pacific Ocean

The magnitude and distribution of precipitation within trade wind clouds east of the Hawaiian Islands and the efficiency of these clouds in returning water evaporated from the ocean surface back to the ocean through precipitation are examined using high-resolution visible and infrared DMSP satellite data and 5-cm wavelength radar data collected during the 1990 Hawaiian Rainband Project. The analyses indicate that on average, precipitation rates greater than 0.1 mm h^-1 occur over about 11% of the area occupied by trade wind clouds at any given time, while about 1.5% of the cloudy areas had rainfall rates which exceeded 1.0 mm h^-1. None of the clouds in the sample had precipitation rates exceeding 10.0 mm h^-1. The average precipitation rate was 1.1 mm d^-1. An estimate of the precipitation efficiency of the trade wind clouds, made by comparing the latent heat input into the atmosphere due to precipitation with the ocean surface latent heat flux, suggests that clouds in the trade wind regime are no more than 20-30% efficient in returning evaporated water vapor to the ocean through precipitation processes.