Current Affairs

Issue

The unusually high number of cyclones in the Arabian Sea, some of them extremely severe with high wind speeds, is a result of warming seas and changes in sea surface temperature distribution.

 

Background

According to India Meteorological Department, the ratio of cyclones in the Arabian Sea is normally 1:4. But this is set to change due to other new factors.

 

Details

• The number of extremely severe cyclonic storms (ESCSs) over the Arabian Sea since 1998 is increasing especially during the post-monsoon season (October-December). The climate models suggest this increase is largely due to global warming.

• Regarding the increase in ESCSs during the post-monsoon season, scientists found three factors may be related.

• One is the rising sea surface temperature, especially over the Arabian Sea. This warm ocean contributed to intensifying cyclones, leading to more severe storms in the Arabian Sea.

• The second factor is that onset of winter monsoon is delaying, leading to a longer storm season.

• The last factor is increases in anthropogenic aerosols, leading to changes in sea surface temperature distribution that in turn change monsoon circulation, resulting in more active storms.

• In general, when global warming proceeds, the surface ocean gets warmer. This warm condition is favorable for intensification of tropical cyclones.

• But increasing greenhouse gasses also causes warming in the upper atmosphere, which makes the atmosphere more stable. This stable atmosphere is unfavorable for tropical cyclones.

• Therefore, the frequency of tropical cyclone genesis would decrease when global warming proceeds. But once a storm generates, the storm can develop into an intense storm due to the warmed surface ocean.

• The climate models suggest an increasing frequency of severe storms over the Arabian Sea during the post-monsoon season, especially during the post-monsoon season.