Mesoscale variability along the east coast of India in spring as revealed from satellite data and OGCM simulations |
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| Authors: | Prescilla Kurien Motoyoshi Ikeda Vinu K Valsala |
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| Institution: | (1) Marine Biological Laboratory, Department of Zoology, Andhra University, Waltair, India;(2) ICMAM Directorate, Ministry of Earth Sciences, NIOT Campus, Chennai, India; |
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| Abstract: | Since mesoscale features like meanders have great importance in nourishing the coastal fisheries, satellite data analyses
and a numerical modeling study were carried out for the east coast of India during spring inter-monsoon time (March-May),
when biological productivity is high. During this time, the East India Coastal Current (EICC) system appears as a northward
flowing western boundary current of a seasonal subtropical gyre in the Bay of Bengal prior to the summer monsoon with a more
intense upwelling in the coastal region. A relatively clear sky permits satellite remote sensing of Sea Surface Temperature
(SST) and Chlorophyll-a (Chl-a), whose patterns were verified against geostrophic velocity in altimeter data: i.e., phytoplankton
grows in colder and nutrient richer water bounded by the seaward meanders. Progression of meanders in the coastal current
was revealed and compared with an eddy-resolving Ocean General Circulation Model (OGCM), which is capable of modeling wind-driven
general circulation and each stage of the meander growth. The numerical solutions provided the following results, in reasonable
agreement with the linear stability theory using a two-and-a-half layer quasi-geostrophic model. Baroclinic instability plays
a key role for the meander growth and eddy generation, while meanders in the coastal current are initiated by isolated mesoscale
rotations propagating westward. The baroclinically unstable meanders have a wavelength of 500∼700 km, grow in one month and
propagate downstream of the coastal current at several kilometers per day. The instability is not strong enough for the meanders
to detach an eddy from the western boundary current. |
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