Context: October to December period is among the favorable months for the development of tropical cyclones in the Bay of Bengal and the Arabian Sea. However, October 2020 passed without witnessing a cyclonic storm.
About Tropical cyclones or hurricanes
- Location: They use warm, moist air as fuel and therefore form over warm ocean waters near the equator.
- Mechanism :
- When the warm, moist air rises upward from the surface of the ocean, it creates an area of low air pressure below.
- After this, the air from the surrounding areas, which has higher pressure, enters this space, eventually rising when it becomes warm and moist too.
- As the warm and moist air continues to rise, the surrounding air will keep entering the area of low air pressure.
- Ultimately, when the warm air rises and cools off, the water in the air forms clouds.
- And this corresponding system of clouds and winds continues to grow and spin, fuelled by the ocean’s heat and the water that evaporates from its surface.
- As such storm systems rotate faster and faster, an eye forms in the center.
- Storms that form towards the north of the equator rotate counter-clockwise.
- On the other hand, those that form south of the equator spin clockwise because of the rotation of the Earth on its axis.
- No difference between a hurricane and a tropical storm
- Depending on where they occur, hurricanes may be called typhoons or cyclones.
- As per NASA, the scientific name for all these kinds of storms is tropical cyclones.
- The tropical cyclones that form over the Atlantic Ocean or the eastern Pacific Ocean are called hurricanes.
- On the other hand, tropical cyclones that form in the Northwest Pacific are called typhoons.
Causes of no cyclone developments this year
- Weak La Nina development: IMD officials have attributed it to the weak La Nina conditions along the equatorial Pacific Ocean.
- Cooler than normal sea surface temperatures over this region—termed as La Nina has been prevailing since August 2020.
- Favorable Madden Julian Oscillation (MJO) phase: Because Madden Julian Oscillation (MJO) was positioned in a favorable phase, the low-pressure systems intensified maximum up to a deep depression.
- MJO is kind of an eastward-moving cyclic weather event along the tropics that influences rainfall, winds, sea surface temperatures and cloud cover. They have a 30 to 60-day cycle.
- High wind shear: There was the high wind shear noted between the different atmospheric levels, last month.
- The vertical wind shear created due to significant wind speed difference observed between higher and lower atmospheric levels prevented the low-pressure systems and depression from strengthening into a cyclone.
Cyclones making landfall on Indian coasts:
- Annual Stats: About 80 cyclones are formed around the world annually, out of which five are formed in the Bay of Bengal and the Arabian Sea, together known as the North Indian Ocean.
- The area affected: India’s east and west coasts are prone to cyclones with the maximum associated hazards rain, heavy winds and storm surge faced by coastal districts of West Bengal, Odisha and Andhra Pradesh.
- Season: Cyclones in the North Indian Ocean are bi-modal in nature, that is, they occur during two seasons as follows
- April to June (pre-monsoon) and
- October to December (post-monsoon)
- Of these, May and November remain the most conducive for the development of cyclones.