A team of Indian scientists has uncovered the dynamics of how vertical air movements over the Himalayas have shaped the Indian summer monsoon that has been the lifeline of South Asia for centuries, which could enhance the accuracy of rainfall forecasts and also help in better assessment of air quality over the sub-continent.
Scientists are constantly looking towards ways to improve the prediction of the Indian monsoon for agriculture, water management and disaster preparedness across South Asia, where millions of people rely on rainfall for their livelihoods.
However, limited studies on the vertical air movement in this region so far have relied on indirect balloon or satellite-based measurements, which cannot capture the long-term fine-scale variability of vertical air motion in the complex Himalayan terrain.
New insights into the hidden patterns of airflow over the Himalayas are now making this possible. Researchers from ISRO’s Space Physics Laboratory, Thiruvananthapuram, Aryabhatta Research Institute of Observational Sciences (ARIES), Nanital, and the University of Kerala, carried out the first direct and high-resolution measurements of vertical air motion during the Asian Summer Monsoon (ASM) months over the central Himalayas during the monsoon months, according to information shared by the Ministry of Science and Technology.
For this they used long-term observation data from the indigenously developed Stratosphere-Troposphere (ST) Radar located at the ARIES campus in Nainital in the central Himalayas. This radar helped them ‘see’ the wind, sensing the faintest vertical motions of air.
The vertical motion of air is an important parameter that gives insight into the atmospheric dynamics and transport and exchange of air mass across the tropopause, which is the 8-18 km high layer between the troposphere, where weather events happen, and the stratosphere, the stable layer above it.
For two years the researchers pointed this radar upwards, collecting thousands of hours of data. The radar-based measurements from this study filled a critical gap, providing the first continuous, precise, and high-resolution measurements of mean vertical air velocity as low as 5 cm per second or 0.18 kph over the Himalayas in all-weather conditions. This, according to scientific data, is calm or still conditions where smoke rises vertically.
They identified persistent downward-moving air between 10 and 11 km above the Earth’s surface, a new feature that reveals a distinct band of descending motion in the upper troposphere during the monsoon months. This, the researchers said, indicated that vertical circulation is more complex than previously understood, with alternating bands of rising and sinking air.
“The study also shows clear variations in vertical air movement in the lower and middle troposphere, while the steady upward air flow above 12 km stayed mostly unchanged,” the researchers said. “These results provide new insights into how air moves vertically, especially the slow, steady rise above 12 km and the “two-step” process that carries air from the lower troposphere to the stratosphere,” they added.
The research, published in, ‘Earth and Space Science’, a peer reviewed journal of the American Geophysical Union, holds immense potential for developing more accurate weather forecasts, strengthening early warning systems and improving climate models that can protect agriculture, water resources, and human health, the Ministry said.
Understanding the vertical motion will also enhance assessments of pollutants and greenhouse gas transport, thereby contributing to improved air quality management and more effective climate change mitigation strategies.
