FEEDER-CELL INGESTION OF SEEDING AEROSOL FROM CLOUD-BASE DETERMINED BY TRACKING RADAR CHAFF

Questions of delivery, transport, and dispersion of cloud seeding aero sol in a convective feeder cloud are addressed by using radar chaff as a surrogate for aerosol and tracking it with circular-polarization ra dar. In a case study, a line source of chaff was released by an aircra ft at the roots of a growing cloud flanking and feeding into a thunder storm line. The chaff was tracked as it dispersed in the boundary laye r and rose more than 3 km from the cloud base at +14 degrees C to leve ls cold enough to nucleate ice-forming seeding aerosols. Quantitative measures of the rates of loft and dispersion, and the volume filling a nd dilution were obtained. The measurements permit examination of the hypotheses and potential efficacy of cloud-base seeding to increase ra in and suppress hail. Notably, the problem of delivery, transport, and dispersion of cloud seeding aerosol is much the same as the air quali ty question of the nature and effect of cloud venting of the boundary layer, and the findings here apply in that context as well.