| dc.description.abstract |
The present study on upper ocean responses to atmospheric forcing (associated with
cyclone passage) in North Indian Ocean revealed significant variability between AS and
BoB. The analysis of cyclone frequency during 1947 to 2006 exhibited lesser frequency
of cyclones in AS than that of BoB. The analysis also revealed significant reduction in
cyclone frequency after the year 1976 with substantial reduction during monsoon season.
The long term SST data at selected points in AS and BoB could not reveal any relation
with reduction in cyclone frequency. However the SLP at same locations exhibited
considerable increase during mid 1970’s, which could have contributed to the observed
reduction in cyclone frequency after the year 1976.The response in waves during cyclone passage exhibited significant asymmetry on either
side of the track in AS and BoB and the response is observed at 100’s of kilometers away
from the track. The significant clockwise rotation in wave direction is observed on the
right side of the track starting from near the track to far away locations, which existed for
a longer duration. However, the anticlockwise rotation in wave direction is observed over
a shorter distance on the left side of the track and dissipated immediately.Inertial oscillation is observed in surface current and in the mixed layer temperature
associated with cyclone passage, which revealed the role of relative location(s) on either
side of the track. The inertial peak closer to the local inertial period indicates maximum
transfer of energy during the cyclone passage in both AS and BoB. The absence of strong
inertial oscillation even with clockwise rotation in surface current and wind indicates the
dominant role of duration of strong wind in generating inertial oscillation.The oceanic response associated with cyclone passage reveal the variable response(s)
which depends on cyclone intensity, the proximity to track and cyclone translation speed.
It is observed that resonance with wind generates higher response in surface current,
wave and SST on the right side of the track and it lasts for a longer duration. The
maximum oceanic response is observed at a few kilometers away on right side of the
track. However lesser rightward bias in the location of maximum cooling is observed for
cyclones with low cyclone translation speed. The response on the left side of the track is
less and is limited over a shorter distance and dissipates immediately. It is observed that
the ocean response, in general, increases with intensity of cyclones. However the
differential cooling produced by the same intensity cyclones in AS and in BoB indicates
the dominant role of low cyclone translation speed in oceanic response.The surface cooling exhibited strikingly differential responses between AS and BoB. The
TMI-SST and buoy observations exhibited significant cooling for a longer duration in AS
compared to that of BoB. The spatial extent of cooling is also much higher in AS than
that of BoB. The wide spread cooling associated with cyclone passage in AS indicates
the dominant role of thermal structure in oceanic response in AS than that of BoB. |
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