Monsoon rains in India. (Photo : Rajarshi Mitra)
Variations in the ability of sand particles flung into the atmosphere from deserts in the Middle East to absorb heat can change the intensity of the Indian Summer Monsoon, said new research from The University of Texas at Austin led by Chinese researchers.
The Indian monsoon from June to September is a period of intense rainfall. Over a billion people rely on the monsoon to bring rains to farmlands, especially in India. The monsoon accounts for up to 80 percent of the annual rainfall in the Indian subcontinent.
But increasing the strength of the monsoon can lead to flooding that can cause massive losses in life and crops.
The study was led by Qinjian Jin, a postdoctoral researcher at the Massachusetts Institute of Technology, who conducted the research while earning his Ph.D. at The University of Texas at Austin's Jackson School of Geosciences. He collaborated with Zong-Liang Yang, a professor in the Jackson School's Department of Geological Sciences and Jiangfeng Wei, a research scientist in the department.
The deserts of the Middle East are a large source of "mineral dust," small particles of sand brought into the atmosphere by wind and thermals. Once in the atmosphere, the dust can heat parts of the atmosphere by absorbing energy from sunlight.
Researchers found that mineral dust from the Middle East can strengthen the Indian Summer Monsoon by heating the atmosphere above the Iranian Plateau and the Arabian Sea. But the dust's ability to absorb heat affected how much the dust influenced the monsoon. Dust that absorbed heat more efficiently was linked with increases in monsoon rainfall.
Jin said the heating ability of dust aerosols largely determines how the monsoon responds to dust. He and the other researchers examined the impact of mineral dust on monsoon strength by creating seven high-resolution computer simulations that varied the heat absorption of mineral dust.
Jin said that for climate models to accurately capture monsoon behavior, they must account for the variability in mineral dust's heat absorption.
"This heating is represented in very different ways in different climate models, and is one of the factors responsible for inconsistency of climate model results," said Jin. "This study addresses the necessity for developing a new method to represent dust heating in climate models."
Jin said he is planning future research on how dust particles can influence climate by changing cloud formation and behavior. He noted dust particles have been shown to be efficient ice nuclei, which may influence the monsoon by changing clouds' properties.
Future research also needs to consider other dust processes, such as the surface erodibility of different dust source regions and how dust enters into the atmosphere, both of which have been studied by Yang and his other collaborators.
"Ultimately, this integrated research will improve our understanding of complex dust-monsoon interactions," said Yang.
The results of the study could help improve monsoon prediction models, which usually use a constant value for sand particles' heat-absorbing ability.
