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Role of subtropical Rossby waves in governing the track of cyclones in the Bay of Bengal
  • Vineet Kumar Singh,
  • Roxy Mathew Koll,
  • Medha Sachin Deshpande
Vineet Kumar Singh
Indian Institute of Tropical Meteorology

Corresponding Author:[email protected]

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Roxy Mathew Koll
Indian Institute of Tropical Meteorology , Dr. Homi Bhabha Road, Pashan, Pune ,INDIA
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Medha Sachin Deshpande
Indian Institute of Tropical Meteorology, Pashan Road, Pune, INDIA.
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The cyclones during November in the Bay of Bengal follow two distinct tracks. Some cyclones move west-northwestward and make landfall at Odisha, Andhra Pradesh, Tamil Nadu or Sri Lanka coast while others move north-northeastwards and make landfall at West Bengal, Bangladesh or Myanmar coast. We found that there is a difference in the steering winds governing these two different cyclone tracks. The north-northeastward moving cyclones are associated with an anomalous upper-level cyclonic circulation over India which is a part of a sub-tropical wave train. This wave train is triggered by an anomalous upper-level convergence over the Mediterranean region near the subtropical westerly jet entrance. The jet acts as a Rossby waveguide and excites an eastward propagating wave train which propagates from the East Atlantic/Mediterranean region and reaches the Indian subcontinent in four days. This wave train induces an anomalous cyclonic circulation over Indian landmass and provides south-to-north and west-to-east steering over the Bay of Bengal causing the cyclones to move in a north-northeastward direction. On the other hand, for west-northward moving cyclones, there is no Rossby wave intrusion over the Indian subcontinent, hence the cyclones move in west-northwestward direction assisted by the climatological winds which are from east to west over the south and central Bay of Bengal. This shows that the track of the cyclone in the north Indian Ocean can be modulated by the atmospheric changes in the extratropics and can act as a precursor for the prediction of the track of the cyclone in this region.