MONSOON DROUGHTS

Subject: Geography

Context: A team of researchers from the Indian Institute of Science and Cotton University has found that some droughts during monsoon season in India are due to unique North Atlantic disturbance.

Concept:

• Previous research has shown that El Niño events almost always lead to dry monsoon seasons, but not all dry seasons are due to El Niño events. In this new effort, the researchers sought to learn more about other events that might impact monsoon season rains.
• They found that nearly half (10 out of 23) of all droughts in India over the past century did not occur in El Niño years. They also found that in years when there were droughts unrelated to El Niño, there were unique atmospheric disturbances in the North Atlantic Ocean.
• These disturbances, they also found, resulted in the development of currents that disturbed the factors that normally lead to the heavy rains typically associated with monsoon season in South Asia.
• The researchers found that the North Atlantic Ocean disturbances tend to coincide with the sudden drop in rainfall in mid-August.
• During an El Niño year, the rainfall deficit — departure fromdeparture from a long-term average — sets in early around month of June and becomes progressively worse.
  However, the drought during non-Elnino year when analyzed together also seemed to follow a common pattern. First, there was a moderate slump in June. Then , during mid-July to mid – august – the peak season monsoon showed signs of recovery and rainfall amount increased., However , around third week of August rainfall again declined steeply.
• They were not able to explain the nature of such disturbances, however, except to note that they involved winds from the upper atmosphere mixing with cyclonic circulation over the cold water of the North Atlantic.
• The resulting wave of air currents, called a Rossby wave, curved down from the North Atlantic — squeezed in by the Tibeteanplateau — and hit the Indian subcontinent around mid-August, and hit the Indian subcontinent around mid-August, suppressing of rainfall and throwing off the monsoon that was trying to recover from the June slump.