Evaluation of Mali, West Africa airborne measurements to access the potential of enhancing precipitation using cloud seeding techniques

Their is a pressing necessity today for world-class scientific research on precipitation enhancement due to the desirer to start operational cloud seeding programs in many parts of the world. Since cloud and aerosol properties can vary significantly from one geographical region to another, and with the time of year in the same region, it is necessary to conduct airborne measurements to access the potential of cloud seeding techniques before blindly adapting a techniques that seems to work in another region. The potential to enhancing precipitation is strongly dependent on the natural microphysics and dynamics of the clouds that are being seeded; therefore, a technique that works in one region may not even work in another region or may not be the best technique to employ.

To assess the potential that cloud seeding cloud have on increasing precipitation, 80 hours of airborne measurements were conducting during the 2007 wet season in Mali, West Africa. The airborne measurements objectives were to determine if cloud seeding in Mali could be beneficial and to help determine the optimal seeding method that should be employ for enhancing precipitation during operational cloud seeding. Cloud condensation nuclei (CCN) concentrations (1% supersaturation) measured just below cloud during aircraft flights conducted through out September 2007 were approximately 500 ± 400 #/cm3. These mid-wet season concentrations are similar to lower tropospheric summer season CCN concentration (445 ± 400 #/cm3) measured in Wyoming and indicates that mostly clean continental conditions are present during the middle of the wet season in Mali. Even when a layer of high CCN concentrations is observed (September 17, 2007), it may be well below cloud base and may not influence the cloud droplet concentration of treatable clouds.

Hygroscopic cloud seeding is predicted to be ineffective or of limited effect under very clean continental conditions; therefore, the operational cloud seeding program in Mali should consider employing other seeding methods (AgI seeding at -10 C) during the middle of the rainy season and use hygroscopic seeding when the CCN concentration is higher. Future measurements should determine the CCN concentrations at the start (June) and end (October) of the rain season in Mali.