Wind Shear Effects on Water Accumulation and Rain Duration in Hawaiian Warm Clouds

Abstract

Aircraft observations of warm rain in Hawaii were analysed concerning the effect of wind shear on the drop growth processes in different cloud types. Drizzle formation is slowed near the cloud top when a strong wind shear exists in an isolated cumulus clouds or a band clouds, while drizzle formation is accelerated with presence of a strong wind shear in cloud clusters. A moderate updraft is needed for raindrops to grow near the cloud top. As drops fall through a cloud, rainwater is accumulated best in cloud clusters and least in isolated cumulus clouds. Rain duration becomes shorter with a strong wind shear in isolated cumulus clouds, but rain lasts for a long period of time from band clouds where the wind is parabolic in form and a strong wind blows at the middle of the trade wind layer.