Cloud Seeding Effects on Precipitation Intensity and Duration of Wintertime Orographic Clouds

The nature of precipitation changes resulting from seeding cold orographic clouds is examined by separating the observed total precipitation change into duration and intensity change components. The total precipitation change and its two components are then evaluated as functions of cloud temperature using precipitation data recorded in the primary target area during the cloud seeding experiment conducted near Climax, Colo. The results show that the total change in observed precipitation is mainly controlled by changes in precipitation duration, rather than intensity. The main effects of seeding appear to be the initiation of a precipitation release for the warmer clouds during many hours when it would not have occurred naturally, and the suppression of precipitation for the coldest clouds during some hours when it would have occurred naturally. These results are consistent with the concepts of cloud microstability and cloud over-seeding.