Abstract
Electrification and precipitation mechanisms were studied in maritime shallow warm clouds around the island of Hawaii.
Ion-drop interaction during drop evaporation is assumed to be the principal charge separation mechanism in warm clouds. During showers a negative potential gradient is observed at the ground, probably caused by negative ions transported from the cloud top to the ground by downdrafts.
Giant nuclei do not contribute significantly to the initiation of warm rain. Most drop growth occurs near the cloud top where the updraft speed decreases with height. Raindrop formation near the cloud top is required to initiate rain beneath the cloud base. The rate at which raindrops form depends mainly on the humidity profile in the trade wind layer. The rainwater accumulation rate varies with the cloud type.
Unsolved problems related to both cloud electrification and precipitation mechanisms are discussed to encourage future research in the tropics.
