Rain Rate

Rain rate is the intensity of precipitation reaching a surface, the depth of rainfall per unit time, usually in millimeters per hour. At sea it is hard to measure directly because there are few gauges; instead it is retrieved from radar reflectivity through a Z-R relation, from disdrometers that size and count drops, and from satellite passive microwave and dual-frequency precipitation radar. Rain freshens the ocean surface, contributes the precipitation term of the freshwater flux E-P, and can form a shallow rain-induced fresh lens that stratifies the surface. The TRMM and GPM missions provide global rain-rate fields.