Ppt on Principles And Techniques Of Artificial Rainmaking And Cloud Seeding

Weather modification, particularly through artificial rain making and cloud seeding, involves the deliberate alteration of atmospheric conditions to enhance precipitation. Techniques such as hygroscopic and glaciogenic seeding are used to increase rainfall, mitigate drought, and reduce hail damage. Understanding the principles, methods, and applications of cloud seeding is essential for students in meteorology, agriculture, and environmental sciences. Key concepts include cloud classification, precipitation mechanisms, seeding agents, weather modification, and drought mitigation.
Introduction to Weather Modification
  • Weather modification is the intentional alteration of atmospheric processes to influence local weather.
  • Artificial rain making and cloud seeding are primary techniques used to enhance precipitation.
  • Applications include drought mitigation, hail suppression, and fog dispersal.
Principles of Rainmaking and Cloud Classification
  • Clouds are classified as warm (cloud top temperature > 0°C) or cold (cloud top temperature < 0°C).
  • Precipitation requires condensation nuclei, which differ for warm and cold clouds.
  • Hygroscopic materials are used for warm clouds; ice-forming nuclei for cold clouds.
History of Cloud Seeding
  • Cloud seeding research began in the 1940s with Vincent Schaefer's experiments using ice crystals.
  • Silver iodide was later adopted due to its structural similarity to ice.
  • Programs expanded globally but faced challenges in proving consistent effectiveness.
Cloud Seeding: Definition and Purpose
  • Cloud seeding is the process of introducing artificial nuclei to induce precipitation from rain-bearing clouds.
  • Methods vary for warm and cold clouds, using aircraft or ground-based generators.
  • Main goals: increase rainfall, augment snowfall, mitigate hail, and disperse fog.
Mechanisms of Cloud Seeding
  • Hygroscopic seeding targets warm clouds to enhance droplet coalescence.
  • Glaciogenic seeding targets cold clouds to promote ice crystal formation.
  • Seeding agents can be delivered by aircraft or ground-based systems.
Applications of Cloud Seeding
  • Increasing precipitation for agriculture and water supply.
  • Augmenting snowfall to boost water resources and hydropower.
  • Mitigating hail damage to crops and property.
  • Dispersing fog to improve visibility and safety.
Seeding of Cold Clouds
Methods:
  • Dry Ice Seeding: Uses solid CO2 pellets released from aircraft over cloud tops.
  • Silver Iodide Seeding: Releases AgI particles as smoke from aircraft or ground generators.
Dry Ice Seeding:
  • Dry ice forms ice crystals as it falls through the cloud, inducing precipitation.
  • Requires large quantities and specialized aircraft; less economical.
Silver Iodide Seeding:
  • AgI acts as efficient ice nuclei at temperatures below –5°C.
  • Requires smaller quantities; can be dispersed over larger areas.
Seeding of Warm Clouds
Water Drop Technique:
  • Large water droplets (25 mm) are sprayed from aircraft to initiate coalescence.
Common Salt Technique:
  • Sodium chloride (NaCl) is used as a hygroscopic agent, dispersed as solution or solid.
  • Spraying can be done by aircraft, ground generators, or balloon bursts.
Summary and Limitations
  • Cloud seeding can enhance precipitation, but effectiveness varies with cloud type and atmospheric conditions.
  • Potential risks include environmental concerns and unintended weather impacts.
  • Further research is needed to improve reliability and assess long-term effects.