Maharashtra: Making clouds rain with dry ice and silver iodide

The state cabinet's decision to opt for cloud seeding to bring about artificial showers in the rain shadow region of Maharashtra coincides with an ongoing cloud seeding experiment launched in Solapur district last year.

CAIPEEX, or Cloud Aerosol Interaction and Precipitation Enhancement Experiment, was undertaken to understand how clouds and aerosols interact and influence the climate.

The experiment was initiated by the Indian Institute of Tropical Meteorology (IITM), which had carried out three similar experiments earlier, twice in Hyderabad and once in Varanasi.

For the exercise, a seeder and an instrumented research aircraft are used to seed clouds and record the changes in them that lead to rainfall. During the 2017 monsoon, weathermen flew airplanes loaded with silver iodide which was sprayed through clouds above Solapur to kick-start their three-year investigation.

To implement Tuesday's cabinet decision, the state government has deployed a C-band radar and an aircraft at Aurangabad in Marathwada to spray dry ice and silver iodide on 100 clouds, and then compare them with 100 unseeded clouds.

The ground radar will track the clouds and verify which ones contributed to rainfall. Maharashtra has toyed with the idea of cloud seeding since 2003, owing to the frequency with which droughts afflict the state.

In August 2003, the state signed an agreement with the Weather Modification Inc (WMI) and its Indian representative for a 90-day exercise to make it rain artificially. In 2015, the state carried out cloud seeding in Marathwada, which led to 1,300 mm rainfall.

A Pune-based scientist explained that cloud seeding involves four stages. First, silver iodide is released into the atmosphere with the help of a rocket or a ground propeller, then the iodide particles rise into the clouds, freezing the moisture. The particles act as a base for water vapour to settle on, and the water vapour crystallises, falling down as snow or rain.

A state government officer informed DNA that the Chinese government had also extended its help for cloud seeding in the past.

Shower Power

• CAIPEEX studies precipitation in rain shadow areas, collects seeding samples to develop protocol for cloud seeding 
• In its phase III in 2015, CAIPEEX clocked 820 hours of airborne observations over India 
• For its phase IV which started in 2017, many ground instruments were set up in Solapur — core of the rainshadow area