Not only El Nino, aerosols too affect influence monsoons, says IIT Bombay study
High concentration of aerosols in the atmosphere influences rainfall in India, revealed a study by the Interdisciplinary Programme in Climate Studies (IPCS) at the Indian Institute of Technology, Bombay.mumbai Updated: Mar 29, 2017 11:38 IST
It’s not just global weather phenomena like El Nino or La Nina that determine the strength of the monsoon, but also concentration of suspended particles — aerosols. High concentration of aerosols in the atmosphere influences rainfall in India, revealed a study by the Interdisciplinary Programme in Climate Studies (IPCS) at the Indian Institute of Technology, Bombay.
A three-member team studied satellite and ground-based observations of aerosol and cloud properties between 2000 and 2009, over the core monsoon region of India – central north-east, central west, and north-west – that records 85% of rainfall. Aerosols are tiny solid and liquid particles in the air that originate from man-made activities such as burning of agricultural waste and forests, biomass burning industries, power plant smoke, as well as in natural form like dust, volcanic ash and sea salts.“When we looked at the data separately in abundant and deficient monsoon years, we found that a mix of atmospheric particles and dust are modifying clouds, thereby affecting rainfall patterns,” said professor Chandra Venkatraman, co-author and convener, IPCS.
Researchers said understanding aerosol-cloud-rainfall interactions could help improve the physics of climate models for climate prediction.
During monsoon breaks, the levels of suspended particles start building up. The team found that during years of deficient rainfall, higher concentration of aerosols resulted in smaller cloud drop sizes, shallower cloud heights and less cloud-ice formation. However, in years the country received abundant rainfall, higher aerosol levels resulted in the opposite.“We know that changes in cloud properties with increased aerosol levels during deficient years could inhibit cloud development and rainfall, and a similar phenomenon during abundant years could lead to cloud invigoration and intensify rainfall,” said Venkatraman.
Deficient rainfall years are marked by lower availability of moisture, less upward wind motion (convection), along with less cloud coverage. On the other hand, abundant rainfall years have higher vertical wind and moisture transport.While large-scale processes such as El Nino, La Nina, sea surface temperature and ocean warming have been well-studied, researchers said the impacts of local processes such as aerosols and deforestation on the monsoon need attention. “Long monsoon breaks of more than seven days can lead to rainfall deficits and impact crop production. Therefore, studies need to be conducted to see if aerosols are intensifying deficits in rainfall in some regions or invigorating with great intensity,” said the IPCS team.
WHAT ARE AEROSOLS?
Aerosols are tiny solid and liquid particles in the air originating from manmade activities such as burning of agriculture waste and forests, biomass burning industries, power plants smoke, as well as natural in the form of windblown dust, volcanic ash and sea salts.
Global studies are on to understand the impact of aerosols on the environment. Researchers said certain aerosols are important, while some are bad for the climate and health
Man-made aerosols comprising carbon and sulphur compounds that are being emitted by industries and vehicles in large quantities are harmful and toxic
Increasing concentration of aerosols in the atmosphere can block sunlight, and affect visibility
On the other hand, if there is solar light but there no aerosols in the atmosphere, human beings will not survive due to the amount of heat in the atmosphere. Naturally occurring aerosols cool the earth.
The paper ‘Contrasting influences of aerosols on cloud properties during deficient and abundant monsoon years’ by PhD students Nitin Patil and Prashant Dave, with Professor Chandra Venkataraman was published in Scientific Reports of the Nature Publishing Group (NPG) on March 24, 2017.