Playing god in the heavens

Playing god in the heavens - Pune - City - The Times of India TNN, Sep 29, 2009, 04.44am IST

PUNE: As the Phase-I of the special cloud research programme in the country entered its final stage, scientists of the city-based Indian Institute of Tropical Meteorology (IITM) who are leading this project have claimed that, using the data collected in the first phase, a more scientific cloud seeding initiative could be undertaken next year.

The Phase-I of the programme called Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) was flagged off from here on May 17, 2009 and would finish on September 30. So far observational missions from Pune, Pathankot, Hyderabad, Bangalore, Bareilly and Guwahati have been completed.

Specially designed, twin-engine Piper Cheyenne N361 JC pressurised aircraft, which can go up to an altitude of 25,000 ft, have been used for the programme. The aircraft have been fitted with scientific instruments.

Elaborating on the importance of cloud seeding, deputy programme manager Mahesh Kumar said, "In many regions of the world, traditional sources and supply of ground water, rivers and reservoirs are either inadequate or under threat from ever-increasing demands resulting from changes in land use and growing population. All fresh water, whether on the surface or underground, comes from the atmosphere in the form of precipitation. This has prompted scientists to explore the possibility of augmenting water supply by means of cloud seeding."

"Atmospheric aerosols have been found playing an important role in cloud microphysics," said B N Goswami, director, IITM. "As the background aerosol distribution and cloud condensation nuclei have changed significantly in the recent years, need for a fresh, scientifically-designed experiment to understand which aerosols modify clouds and lead to precipitation was strongly felt. Hence, the IITM has launched a multi-year, multi-institutional programme, which would address the intricacies of aerosol-cloud-rainfall interactions. The main aim is to study two components, like understanding cloud-aerosol interaction and precipitation enhancement."

Goswami added that, CAIPEEX , which is funded by the Union ministry of earth sciences, would take place in three phases during 2009 to 2012.

Phase-I of the programme was devoted to intensive cloud and aerosol observations using an instrument aircraft over different parts of the country during the period May to September 2009.

Phase-II will be based on the results of Phase-I. A randomised experiment will be carried out in the monsoon and post-monsoon seasons of 2010 and 2011. Statistical methods and numerical model simulations will be used to evaluate the experiment. Two aircraft will be used for cloud microphysics observations and cloud seeding purposes.

The third phase of the programme will be devoted to detailed scientific analysis of the data collected from the first two phases. It would be carried out it 2012.

When asked about the benefits of the programme, programme manager J R Kulkarni said: "One of the requirements for improving the accuracy of numerical weather forecast is high-resolution cloud resolving models. The data collected in the CAIPEEX will be useful for effecting this improvement. Most importantly, the experiment will provide the guiding principles for carrying out operational cloud seeding programmes in a more efficient and economic way."

History of cloud seeding

Cloud seeding is the attempt to change the amount or type of precipitation that falls from the clouds. This is done by dispersing substances that serve as cloud condensation or ice nuclei into the air. It alters the microphysical processes within the cloud and helps in increasing the rainfall.

In the late 1940s, Nobel Prize winner American scientist Irving Langmuir and his colleagues discovered that dry ice, when dropped from an aeroplane into a supercooled cloud deck, caused a rapid conversion of water to ice, leading quickly to the production of snowflakes and dissipation of cloud in the region. They also discovered that silver iodide had same nucleating property.

Later, another method for stimulating the precipitation has been found by injecting salt particles near the base of the cloud to provide centres for droplet formations. After these discoveries, many experiments have been carried out all over the world.

The most common chemicals used for cloud seeding today include sliver iodide and dry ice. The use of hygroscopic materials, such as salt, is gaining in popularity because of some promising research results.

Indian initiative

The first attempt at cloud seeding in India was made in 1952 by S K Banerjee, then director-general of observatories, India Meteorological Department. According to the Indian Institute of Tropical Meteorology (IITM), Banerjee used hydrogen balloons and salt and silver iodide.

The IITM conducted cloud seeding experiments over different parts of the country between 1963 and 1973. The areas covered include Rihand catchment in UP, Thiruvallur in Tamil Nadu, Linganamakki in Karnataka and Mumbai.

The IITM also carried out randomised cloud seeding experiment over Baramati during the period 1973-86. The results showed 24% increase in rainfall.

The 90s witnessed many advances in airborne instrumentation, radars, flares and software.

Cloud seeding programmes with modern technology have been carried out by the governments of Karnataka, Andhra Pradesh and Maharashtra in the years 2003-05 with scientific consultancy of the IITM. The Brihanmumbai Municipal Corporation has carried out cloud seeding during the monsoon season this year.

When conducted in operational mode, it is not possible to delineate the contribution of the seeding to enhancement of rainfall due to the inability of separating the component of rainfall that would have occurred naturally from the same clouds.