Role of West Asian Desert Dust in Modulating Indian Monsoon
The Indian summer monsoon rains are essential for providing the region’s water supply. Recent shifts in timing and strength have challenged scientists to unravel the complex factors that influence monsoon activity. Monsoons result from a complex interplay between solar warming of the air and land surface, dynamical circulation between land and ocean regions, and cloud-aerosol interactions, in addition to various other factors. However, the influence of aerosols alone on monsoon activity seems to be complex and uncertain. Previous theories have examined the roles of both pollution and natural desert dust aerosols. A team of U.S. Department of Energy (DOE) scientists at Pacific Northwest National Laboratory and researchers at the Indian Institute of Technology Bhubaneswar, India, used satellite data and models to show that desert dust aerosol levels over fairly remote regions of the Arabian Sea, West Asia, and Arabian Peninsula are positively correlated with the intensity of summer monsoon rainfall over India. They showed that dust and summer monsoon precipitation vary in concert over timescales of about a week. Global climate model simulations using the DOE/National Science Foundation-sponsored Community Atmosphere Model (CAM5) support this remote link and indicate that, since dust suspended in the atmosphere absorbs solar heating, the variability in dust aerosol loadings can induce larger-scale atmospheric circulation changes, modulating moisture transport over the Arabian Sea and moisture flow into India, thereby changing monsoon rainfall on relatively short time scales. These findings highlight the importance of natural aerosols in influencing the strength of the Indian summer monsoon. Such an aerosol-induced remote link to monsoons was not known before, and the study clearly shows that aerosols of natural origin can have remote effects on large-scale circulations with important implications.
Vinoj, V., P. J. Rasch, H. Wang, J.-H. Yoon, P.-L. Ma, K. Landu, and B. Singh. 2014. “Short-Term Modulation of Indian Summer Monsoon Rainfall by West Asian Dust,” Nature Geoscience 7, 308-13. DOI:10.1038/NGEO2107.