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Ecology & Environment
Mahesh

29/04/24 14:10 PM IST

Anticyclones in India

In News
  • The waning phase of the strong El Niño of 2023 brings the expected warm temperatures across the globe — while cooler temperatures spread from Pakistan across India to West Bengal during March.
Global warming
  • Global warming also creates unique features locally that modulate heat waves on top of cool background temperatures.
  • Heat waves over India have been of special concern this season because of the general elections.
  • Some persistent circulation patterns have been creating heat waves and this pattern should serve as another focal point for improving predictions.
  • It was apparent in March that the anticyclonic circulations over the North Indian Ocean were the drivers of unusual rainfall over Odisha.
  • An anticyclone has winds moving in a clockwise direction, with air sinking down in the middle of it. As this air hits the ground, it is compressed and warmed and can create a high pressure heat dome.
Anticyclones
  • The persistence of the anticyclones is not unusual in and of itself.
  • During the pre-monsoon season, the upper-level Indian Easterly Jet (IEJ) begins to take shape in the upper atmosphere, at around the 10 degrees N latitude, across the Arabian Sea, peninsular India, and the Bay of Bengal.
  • A strong westerly jet exists to the north around 30 degrees N, and the two together can generate an anticyclonic pattern over the Indian Ocean and the Indian subcontinent.
  • An easterly jet refers to strong winds coming from the east while westerly jets come from the west.
  • These are natural seasonal features.
  • The westerly jet is pushed north during the monsoon season and the IEJ dominates the Indian subcontinent.
  • During the pre-monsoon season, a strong anticyclone can bring dry and hot weather over many parts of India while a weak anticyclone produces milder weather.
  • The key question then is whether the anticyclone is strong this year and if that is related to global warming and, thus, the heat waves.
Stages of early warnings
  • Returning to the local manifestation of global warming: accurate early-warning systems take a three-step approach called the ‘ready-set-go’ system, under the so-called ‘Subseasonal-to-Seasonal Predictions’ project of the World Climate Research Program under the World Meteorological Organisation.
  • India is part of this project, has invested heavily in S2S predictions, and has made impressive progress in improving the accuracy of predictions.
  • Preparing the system and guiding the National Disaster Management Agency (NDMA) requires this three-step approach to function efficiently and effectively.
  • Considering there are more than 1.2 million polling stations for the general elections this year, the optimal use of resources to prepare for, mitigate, and recover from extreme events requires location-specific information at each step.
  • The ‘ready’ step provides a seasonal outlook — where the background state, or the external factors (such as global warming and the El Niño), are used to maximise the accuracy of longer-lead forecasts.
  • The ‘ready’ step allows the NDMA, its local agencies, and all local governments to ready their disaster response systems.
  • The subseasonal predictions refer to the extended range of weeks two to four, which contribute to the ‘set’ step.
  • Resource allocations and identifying potential hotspots to move resources including personnel ensure disaster-preparedness is set to go.
  • The ‘go’ step is based on short- (days 1-3) and medium- (days 3-10) range forecasts.
  • At this step, everything hits the road to manage a disaster, including rescue efforts, hydration centres, heat shelters, etc.
Source- The Hindu

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