Unspinning a Cyclone
What were Tauktae and Yaas?
In the second week of May 2021 a severe tropical cyclone “Tauktae” formed in the Arabian Sea, near Lakshadweep Islands. The cyclone was named ‘Tauktae’ – a Burmese name for a rather vocal gecko. Cyclones are named by the World Meteorological society (WMO) with a very interesting method – countries of the region get to submit a name each and these names are then adopted alphabetically alternating between male and female names. 13 countries submitted names for cyclones originating in the Indian Ocean in 2021.
Tauktae is the 5th strongest cyclone recorded in the history of the Arabian Sea since 1998. It hit the Indian west coast on 16th May 2021 and inflicted severe damage through rough seas, heavy rainfall, strong winds and floods. Just 5 days later, as Tauktae travelled through North India diminishing in intensity, a low-pressure area formed in the Bay of Bengal. This developed into another tropical cyclone which reached the West Bengal and Odisha coasts by May 26th. This cyclone was named “Yaas” by Oman and means ‘tree’.
Why did they occur?
Tropical cyclones are oceanic storms and hurricanes that form in low pressure areas with increased sea surface temperatures. Cyclones typically develop above seawater with warm temperatures (minimum of 26.5°C) and hence most originate around the equator. The increased heat in the summer warms the surface of the sea and the resulting evaporation increases warm air just above the water surface. Just as you see steam rising over boiling water, hot air rises up. This creates space – regions of low-pressure – into which cool air rushes in from the surrounding areas. This process causes the circular wind currents that we see even in animated drawings of cyclones. The process continues until concentric circles of a low-pressure region surrounded by strong rotating winds and currents at high pressures are formed. The low-pressure region in the centre is referred to as the ‘eye’ of the cyclone, surrounded by the ‘eye wall’, a high-pressure region. It is the eye wall that is responsible for majority of the destruction caused by a cyclone, it is made of dense clouds and strong winds that are in constant rotation. The outermost layer is mainly clouds with heavy rains that spiral towards the eye.
The warm air and moisture fuels tropical cyclones, with currents and high-pressure winds steering these storms. Most cyclones in the Indian ocean travel above the sea in an anti-clockwise direction before landfall. This is largely due to the Indian Ocean Gyre, one of the five major oceanic gyres.
Seasonality dictates the rotation of oceanic gyres. The Indian Ocean Gyre rotates anti-clockwise in the winter, gradually evolving to less intensity currents by late summer that eventually change direction to rotate clockwise.
How does the IOD impact this?
The Indian Ocean Dipole is characterised by the difference in sea surface temperature in two different areas, or poles of the Indian Ocean. The Arabian Sea is the Western Pole and the eastern pole is just south of Indonesia in the eastern part of the Indian Ocean.
There are two types of Indian Ocean Dipole events – Positive and Negative. Positive phases are when the sea surface temperature in the Western Pole is warmer than the Eastern and the Negative Phase is when the Western Pole is cooler than the Eastern. This irregularity of temperatures leads to low-pressure belts being created at the poles. Along the Indian coastline, IOD events usually result in tropical cyclones and the phases closely precede or follow the ENSO – El Nino southern oscillation events.
Cyclones and India
Most cyclones in the Indian Ocean form during the months of November and May, affecting the coasts of India and Bangladesh. The resulting low-pressure belts at either pole often lead to a change in pressure at the opposing pole. As in the case of the recent cyclones Tauktae and Yaas witnessed in May, Tauktae originated at the western pole drawing in strong winds and high-pressure areas to the ‘eye wall’ of the cyclone. This then created low pressure belts in the Bay of Bengal that fuelled the cyclone Yaas. IOD events begin in May and peak around September or October at the latest before quickly subsiding in the boreal winter (December – February).
Our future with Cyclones
With increasing sea surface temperatures due to global warming, the frequency of IOD events is also increasing. This will inevitably lead to more frequent and possibly more severe cyclones.
IOD events have vast consequences across continents neighbouring the Indian oceans, such as bushfires in Australia and floods in eastern African countries. IOD events and cyclones, similar to ENSO- El Niño Southern Oscillation events result in loss of life, livelihoods, damage to property, loss of marine life and damage to ecosystems. They result in coastal erosion that is largely enhanced by artificial structures along the coast. Buildings, sea walks, coastal roads etc compromise the structural integrity of beaches. Which increases wave and current velocity. The consequences of which are severe during storms and cyclones when the weather is already turbulent.
Image from: https://utkalupdates.com/trending/cyclone-yaas-might-turn-super-cyclone-hit-sundarbans-regional-meteorological-department/
Global warming combined with natural disasters accelerates our alarming loss of biodiversity. These crises are not separate from one another; therefore, their solutions are also intertwined.
Protecting biodiversity and the structural integrity of ecosystems such as mangroves and coral reefs are our greatest mitigation strategies against the impacts of natural disasters. The presence of these ecosystems not only reduces the severity of cyclones but also directly helps reduce sea surface temperatures. However, due to current developments on our coastlines vast areas of mangroves have been deforested, increased activity in the seas such as trawling has led to devastating damage to our barrier reefs. Planting of mangroves and re-generation of reefs is a way to ensure reduced damage due to oceanic events and cyclones.
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Very nicely written and very informative