11-Year Warm Cloud Seeding Experiment in Maharashtra State, India

A warm cloud modification experiment was carried out during the 11-summer monsoon (June - September) seasons (1973-74, 1976, 1979-86) using a double-area cross-over design with area randomization. An instrumented aircraft was used for the cloud physical measurements seeding. Finely pulverized salt (sodium chloride) particles were released into and the monsoon clouds (stratocumulus and cumulus) during aircraft penetrations into the clouds at a height of 200-300 m above the cloud base. The warm cloud responses to salt seeding were found to be critically dependent on the cloud physical characteristics e.g., vertical thickness and the liquid water content. When clouds having (i) vertical thickness > 1 km, and (ii) LWC > 0.5 g m^3 were seeded with salt particles (modal diameter 10 um, concentration 1 per liter of cloud air) produced increase in rainfall of 24 percent significant at 4 percent level. The cloud physical observations made in not-seeded (control) and seeded (target) clouds have apparently provided some useful evidence to illustrate the possibility that the hygroscopic particle seeding might accelerate the collision-coalescence process.