‘Aerosols can enhance monsoon rains’

Study finds correlation between rainfall in India and aerosol levels over W. Asia

Monsoon rains over India could increase if desertification leads to more dust from West Asia and North Africa swirling into the air, suggests a research report being published in Nature Geoscience.

There has been growing interest in examining how fine particles in the atmosphere, known as aerosols, affect the climate. However, much of this research has looked at particles generated by human activity, especially the role of soot.

Aerosol role

But natural aerosols, such as sea-salt and dust, are far more abundant than human-produced ones, remarked V. Vinoj, who is currently with IIT Bhubaneswar. The research appearing online in Nature Geoscience was carried out by him with Philip J. Rasch's group at the Pacific Northwest National Laboratory in the U.S.

Analysing observational data, Dr. Vinoj and his colleagues found that monsoon rainfall during June, July and August over central India was strongly correlated with aerosol levels over West Asia, North Africa and the Arabian Sea.

The scientists turned to a global climate model, the Community Atmosphere Model (CAM5), to simulate what effect different types of aerosols would have on the monsoon. When dust was removed altogether, the correlations between the central Indian rains and West Asian aerosol levels disappeared.

The simulations also showed that when West Asian dust levels dropped, rains over central India decreased within a week.

Low pressure band

The dust acted by absorbing radiation from the sun and heating the atmosphere.

High levels of dust over West Asia and North Africa lowered atmospheric pressure in land regions to the north and west of the Arabian Sea, the scientists said.

That low-pressure band strengthened moisture-laden winds that fed the Indian monsoon.

“The expected expansion of desert and arid regions under global warming could enhance dust transport from the deserts of the Middle East and North Africa to the Asian monsoon regions, further enhancing monsoon rainfall,” observed William Lau of the NASA Goddard Space Flight Center in the U.S in commentary that has been published in the same journal.

Study finds correlation between rainfall levels in central India and aerosol levels over West Asia