Cyclones in north Indian Oceans [i.e in Bay of Bengal & Arabian Sea which
are the real extension of Indian Ocean in the east and west side of India] generally
tend to move in North & north westerly direction. That is why the eastern coast of India is
more prone to cyclone hit than its western counterpart. Similarly recarvature i.e movement in NEly
direction is also a common feature of a cyclone movement. But there is rare evidence that the cyclone
drifted south west wards. Will this drift be caused by the advection of the background potential
vorticity field by the storm circulation?
Because,
[1] The SST from Cape Comorin to Puducherry, especially in Mannar Bay
and in Coramandal coast at least between
Vedaranyam and Marakanam is relatively high than compare to elsewhere in the
Bay.
[2] The horizontal warm air advection in the above said coastal
stretch will lead to the formation of vortex.
[3] This formation may be in SWly direction to the current location of
VSCS.
Beta Drift
The drift of a
tropical cyclone through the large-scale background wind in which it is
embedded is known as Beta drift. The drift is caused by
the advection of the background potential vorticity field by the storm
circulation. Beta drift generally
causes tropical cyclones to move pole ward and westward relative to the motion
they would have if the background potential vorticity field were unperturbed by
the storms. This drift speed is generally around 1–2 m/s.
Courtesy: American Meteorological Society. .
