Uncommon cyclones in Arabian Sea

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Context:

A rare cyclone is forming over Saurashtra-Kutch. This will be the first August cyclone over the Arabian Sea since 1976.

Details

Why cyclone Asna is unusual ?

• Firstly, Cyclone Asna, formed recently in the month of August, which is not a cyclonic season in north Indian ocean. This is the first North Indian Ocean cyclone in August since 1981.
• Secondly, the formation of depression was occurred over land and the cyclone formation was happened over the sea.

Tropical Cyclone Season Peaks in the Northern Indian Ocean

• The northern Indian Ocean has two peaks of tropical cyclone activity.
• The first peak in the northern Indian Ocean occurs from April through June and the second peak is from September into December.

Reason for this dual peak

• The reason for this dual peak in the tropical cyclone season is the Asian Monsoon.
• Typically, right before the monsoon kicks in (April through June) and just after it fades (September into December), there is a window where vertical wind shear relaxes enough for possible strong tropical cyclone development in the northern Indian Ocean.

Tropical cyclone formation conditions: https://www.iasgyan.in/daily-current-affairs/tropical-cyclone-ilsa

Role of the Arabian Sea and Bay of Bengal in Cyclogenesis

• Warming plays a role in cyclogenesis and cyclone numbers in the Indian Ocean.
• Wind patterns and sea surface temperatures influence cyclogenesis over the north Indian Ocean.
• It also has "oceanic tunnels" connecting it to the Pacific Ocean and the Southern Ocean.
• The Pacific tunnel brings warm water in the upper 500 m, while the Southern Ocean tunnel introduces cooler waters below 1 km.
• The Arabian Sea warms rapidly during the pre-monsoon season as the Sun moves to the northern hemisphere.
• The Bay of Bengal is relatively warmer and intensifies atmospheric convection and rainfall.

Reason cited for this unusual phenomena

• Its formation was fueled by prior rainfall and soil moisture, leading to extreme rainfall in western India.
• The combination of global warming, El Niño, and underwater volcanic eruptions possibly amplifies the Indian Ocean.
• More heat is coming from the Pacific, and the Southern Ocean is also warming.

Way ahead and mitigation of these extreme climate events: https://www.iasgyan.in/daily-current-affairs/how-to-prepare-for-extreme-weather-events

 Contrast in cyclogenesis between the Arabian Sea and Bay of Bengal

• The Bay of Bengal is more shallow than the Arabian sea so there is more heat transfer from the water to the air. This increases the potential for moisture and instability, which are necessary ingredients for cyclone formation.
• The geometry of the Bay of Bengal amplifies wind speeds as they funnel into the bay. This increases the destructive potential of any cyclone that forms here.
• The Bay of Bengal is surrounded by land on three sides, which provides a source of additional moisture and instability.
• The Arabian Sea is deeper, so the waves are not as high as in the Bay of Bengal.
• The Arabian Sea is much narrower than the Bay of Bengal, which means that cyclones have a harder time forming.

Monsoon: https://www.iasgyan.in/daily-current-affairs/onset-of-monsoon

Source: https://epaper.thehindu.com/ccidist-ws/th/th_international/issues/98601/OPS/G1SDA8NTP.1.png?cropFromPage=true