Results of Seeding for Dynamic Effects on Rain-Cell Properties in FACE-2

Abstract

Volume scan radar studies incorporating the use of an elaborate method of defining and tracking convective rain cells through their lifetime have been used to a) Explore and verify, in quantitative terms, the basic tenet of the technique of cloud seeding aimed at producing dynamic effects. This technique relates increases in the depth of convective cells, assumed to occur due to this type of seeding, to corresponding increases in the treated cells' rainfall intensity, area and duration of precipitation and, consequently, to the total yield of rainfall volume. b) Employ the data gathered on the gross properties of rainfall of convective cells, namely their heights, intensities, precipitation areas and their durations and total rain volume, to estimate the effect of seeding, if any, on their properties. These studies suggest that seeding convective cells for dynamic effects affected the preceding properties of these cells in a manner that resulted in increases in their total rainfall and that the positive changes in these properties could be predicted from the changes in maximum cell height following seeding. The effect of seeding appears to be strongest for cells treated early in their life cycle with a substantial amount of AgI (i.e., more than 600 g). Seeding effects of 22% increases in cell heights and over 100% increases in cell rain volume are indicated under such seeding conditions. The significance levels of these results are found to be 2.1% and 0.6%, respectively. The positive effects produced by seeding on the AgI treated cells may have resulted in a compensating negative effect on the smaller untreated clouds forming in the vicinity of these treated cells.