Arabian Sea to get stormier, says study

Cyclone Ockhi, which left a trail of destruction in Kerala and Tamil Nadu before moving to the Lakshadweep Islands, offers proof for a recent finding by a team of researchers that extremely severe cyclones are becoming more frequent in the Arabian Sea.

Though Cyclone Ockhi originated in the Bay of Bengal, it gained power as it moved through the Arabian Sea.

In a study published in the journal Nature Climate Change about a fortnight ago, atmospheric scientists, led by Hiroyuki Murakami of Princeton University in the US, reported that the Arabian Sea would throw up more number of deadly storms with wind speeds of 165 km/hr or more.

They blamed global warming for this. In the normal course the Arabian Sea sees one extremely severe cyclone in every four years.

Significantly, three severe storms which developed in the Arabian Sea, , including the 2014 Cyclone Nilofar, left many parts of Gujarat devastated.

In 2015, two systems — other cyclones formed in 2015 – Cyclone Chapala and Cyclone Megh — moved in the opposite direction, hitting the Yemeni island of Socotra.

Unlike the Bay of Bengal, the Arabian Sea rarely generates severe cyclones. For instance, between 1998 and 2013, only five extremely severe cyclones originated in the Arabian Sea.

According to Hiroyuki Murakami, two factors have contributed to the increased severity of Arabian Sea cyclones, particularly post-monsoon.

First, the Arabian Sea surface becomes warmer than the other ocean basins during this period.

Second, and more important, due to the interplay of global warming, climate variability and weather changes, winter monsoon circulation has been weakening over the years.

Speaking to BusinessLine from New Jersey, Murakami said: “It is not clear if Cyclone Ockhi is developing into extremely severe cyclonic storm. It may not be surprising if it does as the Arabian Sea is much warmer this year.”

“This study is consistent with the recent findings by Roxy Mathew Koll and colleagues at the Indian Institute of Tropical Meteorology at Pune that flooding in India has trebled and the moisture is coming from the Arabian Sea,” said Raghu Murtugudde, Professor of Atmospheric and Oceanic Sciences at the University of Maryland.

“After the monsoon season, the vertical shear — changing winds from the surface to the upper atmosphere which tends to remove energy from the cyclone and prevents their strengthening — gets reduced, making cyclone formation more probable,” he said.

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