not much data on western disturbances. According to A P Dimri, professor, school of environment science, Jawaharlal Nehru University, New Delhi, there has been very little research on western disturbances because most researchers prefer to study the monsoon which is considered lifeline of Indian agriculture. R Krishnan,a scientist at the Indian Institute of Tropical Meteorology, says that even defining or counting a disturbance is tricky because when western disturbance moves over a long distance, its strength changes and one can never be sure when a new disturbance gets formed or an existing one undergoes change. These disturbances originate thousands of kilometres away and travel over countries where data collection is sparse. India has facilities to study the weather but observational data from Afghanistan and Pakistan is virtually non-existent, says A Jayaraman, director, National Atmospheric Research Laboratory, Department of Space.
B P Yadav, head of IMD's National Weather Forecasting Centre, says that more disturbances are being observed these days because the technology to detect, monitor and predict has improved. IMD is now undertaking studies to understand western disturbance, Yadav adds. plateau in recent decades has increased the instability of the Westerlies and this has increased the variability of the western disturbances. According to the study, the western Himalayan region has seen a significant rise in surface temperatures since the 1950s.Observations from the area show a significant increase in precipitation in recent decades. The researchers looked at a variety of climate data to understand the increasing frequency of heavy precipitation. They say temperatures have risen in the middle- and upper-tropospheric levels over the subtropics (area between the Tropic of Cancer and the Tropic of Capricorn) and the middle latitudes. “Our study suggests that humaninduced climate change is the reason for the increased variability of western disturbance,” says R Krishnan,one of the researchers.“The findings are based on direct observations and we are now using climate models to confirm if the impact is human-induced,” says Krishnan.
Another study which blames global warming is by Jennifer Francis of Rutgers University, New Jersey, and S J Vavrus of University of WisconsinMadison, both in the US. The study, published in the January issue of Environment Research Letters, suggests that heating up of the Arctic has weakened the jet streams in the northern hemisphere. The west to east flow of jet streams in the northern hemisphere is maintained by the “gradient of heat” between the cool Arctic and warmer areas near the equator. But the Arctic has been warming since the past 20 years due to which the jet streams have become weaker. Rather than circling in a relatively straight path, jet streams now