Warm Rain Development in a Three-Dimensional Cloud Model

Abstract

A warm rainshower was simulated in a shallow, anelastic, three-dimensional cloud model with detailed microphysics. After many features of the drop growth process were successfully simulated in a symmetric cloud, wind shear effects on both microphysical and dynamic properties were investigated. A number of special characteristics appeared under wind shear conditions: 1) the development of stronger downdrafts and a shortened cloud lift; 2) weak rainfall occurs early in the process; 3) a sharp raindrop size distribution; 4) initial rainfall localized in a narrow area at the ground with a large rainfall intensity gradient near the upshear side; 5) greater movement of the cloud system during rainfall; and 6) formation of cyclonic-anticyclonic circulations near the cloud top. Many of these characteristics may be explained by the transport of horizontal momentum by updrafts/downdrafts, as shown by close correspondence with the detailed microphysical processes.