Theme-IV-2-Cloud seeding operations for draught mitigation.

Abstract

Cloud Seeding for Precipitation Enhancement has been carried out by Government of Andhra Pradesh, India in the Rain Shadow (<600 mm) Region of Andhra Pradesh between latitudes 12°36' to 19°08' and longitudes 76°38' to 80°55' covering an area of 1,35,680 km' in the 12 districts during 2003-2009. Mostly the cloud seeding has occurred between the altitudes of 1200-2500 m above mean sea level with an updraft velocity of 0.5-3 m/s. This conforms that these clouds are warm clouds well below the freezing level (5800 m) in the seeding area. Most of the clouds are seeded at the base by releasing hygroscopic material (mostly Calcium Chloride) with the help of pressurized aircrafts fitted with hygroscopic flares. C-Band analogue weather RADARs with TITAN (Thunder Strom Identification Tracking and Now casting) software were used to identify the clouds and to analyze the cloud growth. On an average not more than 23% of the seedable clouds are seeded with the existing infrastructure. It is observed from the RADAR data that there is an increase in Cloud Volume, Area, Reflectivity, Life and Lowering of Centroid after seeding indicating that the Clouds are responding to seeding material. It is also observed in general that, cloud seeding is more effective if we get active monsoon clouds and it is less effective if we get weak monsoon clouds. Overall about 17% of total rainfall could be attributed to cloud seeding during the years 2005-2009.During the Phase-I component of the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) by Government of India, it has been inferred that warm rain processes are suppressed due to the presence of heavy haze over the Indo-Gangetic plains, indicating the necessity of introducing Hygroscopic Giant Cloud Condensation Nuclei artificially to trigger the precipitation processes.