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Saturday, Dec 14, 2019

Arabian Sea witnesses 7 cyclonic disturbances; highest in 128 years

mumbai Updated: Dec 05, 2019 01:09 IST

The Arabian Sea has witnessed seven cyclonic disturbances so far in 2019 – the highest in a year since 1891, when the India Meteorological Department (IMD) started keeping records. In 1998, there were six cyclonic disturbances in the Arabian Sea.

Cyclonic disturbances are rapid weather systems, which include weather depressions, deep depressions, and tropical cyclones (of severe, very severe, extremely severe, and super cyclonic storms depending on their intensity).

Of the seven cyclonic disturbances this year, four developed into cyclones – Vayu (June 10-17); Hikka (September 22-25); Kyarr (October 24-November 2); and Maha (October 30-November 7) — while three were weather depressions — one between September 29 and October 1; and two are currently been recorded over southwest Arabian Sea (developed on Monday; likely to be decl-ared cyclone Pawan) and east central Arabian Sea (developed on Tuesday, but may weaken).

The Arabian Sea usually witnesses a cyclone every year, while the maximum number of cyclones (5) was recorded in 1902.

Mrutyunjay Mohapatra, director general, IMD, said that this year, there were four major factors responsible for increased frequency of cyclonic disturbances – warmer sea surface temperatures, active southwest and northeast monsoon conditions, an active weather phenomenon called Madden-Julian Oscillation (MJO) (eastward moving pulses of clouds and rainfall that help in development of low-pressure systems and tropical cyclones), and the positive India Ocean Dipole (an oscillation of sea-surface temperatures in which the western Indian Ocean becomes warmer than the eastern Indian Ocean).

“It is a fact that the intensity of cyclones and weather disturbances are increasing over Arabian Sea. International studies suggest that this is owing to climate change, but there is no direct correlation that it is due to man-made effects yet,” said Mohapatra. “While it is rare, we have no forecast that this kind of weather events will continue in the coming years.”

In all, 11 cyclonic disturbances have developed over the north Indian Ocean (Bay of Bengal and Arabian Sea). “The activities of Bay of Bengal have been subdued this year, as three cyclones were recorded (Pabuk, Fani and Bulbul) against the normal of four every year,” IMD data stated.

Independent meteorologists said the genesis of such cyclonic disturbances depends upon sea surface temperature, wind pattern and triggering weather events. “Sea-surface temperature has increased in the Arabian Sea in the period of 1981-2010, but the cyclonic disturbances in the region continue to be erratic, with years like 2017 when not a single system formed in the region,” said Akshay Deoras, meteorologist and PhD researcher, University of Reading, UK. “There has been a prominent warming in the Arabian Sea this year owing to the positive phase of IOD and several instances of active MJO.”