Anticyclones
An anticyclone is a weather phenomenon defined as a large-scale circulation of winds around a central region of high atmospheric pressure (They are surrounded by closed isobars having decreasing pressure outward), clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere as viewed from above (opposite to a cyclone).
Effects of surface-based anticyclones include clearing skies as well as cooler, drier air.
The track is highly variable and unpredictable
Anticyclones originated due to the descent of either polar cold air mass or warm tropical air mass.
These anticyclones are high-pressure systems and are more common in subtropical high-pressure belts and polar high-pressure belts where the air is sinking from the upper troposphere to the lower troposphere but are practically absent in equatorial regions
The formation of anticyclonic conditions at polar high-pressure belts is a thermal phenomenon as these bills a thermally direct whereas the formation of anticyclonic conditions at subtropical high-pressure belts is a dynamic phenomenon as these bills are thermally indirect
What links anticyclones to heat?
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 record warming of 2023 has so far not been fully explained since it was much warmer than what we expected just from the superposition of El Niño on global warming.
But the impact of the El Niño during its pre-monsoon demise on the IEJ tends to produce a stronger and more persistent anticyclone and thus longer lasting and more intense heat waves.
So, the heat wave season this year is consistent with the warmer temperatures due to the El Niño itself as well as the ‘steroids’ being added by the unexplained warming of 2023
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.
Preparedness and recovery
All evidence suggests India’s prediction system and early warning systems continue to improve and the NDMA has worked these details well into its ‘ready-set-go’ system.
The remaining challenges are to build resilience for the future by better predicting the trajectory of the weather at every location over India.
This is a significant challenge but budding efforts for predictions at 10-year timescales have shown promise.
The coordination from national to neighbourhood levels and early-warnings from days to a decade are taking shape.
Governments, their departments, and the people at large need to be trained and engaged with to make this a sustained success.
India’s dream of sustained economic development depends on this.
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