Observed oceanic response to tropical cyclone Jal from a moored buoy in the south-western Bay of Bengal
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Upper oceanographic and surface meteorological time-series observations from a moored buoy located at 9.98°N, 88°E in the south-western Bay of Bengal (BoB) were used to quantify variability in upper ocean, forced by a tropical cyclone (TC) Jal during November 2010. Before the passage of TC Jal, salinity and temperature profiles showed a typical BoB post-monsoon structure with relatively warm (30 °C) and low-saline (32.8 psu) waters in the upper 30- to 40-m layer, and relatively cooler and higher salinity (35 psu) waters below. After the passage of cyclone, an abrupt increase of 1 psu (decrease of 1 °C) in salinity (temperature) in the near-surface layers (up to 40-m depth) was observed from buoy measurements, which persisted up to 10–12 days during the relaxation stage of cyclone. Mixed layer heat budget analysis showed that vertical processes are the dominant contributors towards the observed cooling. The net surface heat flux and horizontal advection together contributed approximately 33 % of observed cooling, during TC Jal forced stage. Analysis showed the existence of strong inertial oscillation in the thermocline region and currents with periodicity of ∼2.8 days. During the relaxation stage of the cyclone, upward movement of thermocline in near-inertial frequencies played significant role in mixed layer temperature and salinity variability, by much freer turbulent exchange between the mixed layer and thermocline.
KeywordsBay of Bengal Tropical cyclone Upper ocean response
The encouragement and facilities provided by the Director, INCOIS, are gratefully acknowledged. We would also like to acknowledge two anonymous reviewers, whose comments and suggestions greatly improved the manuscript. Ocean observation programme of the National Institute of Technology (NIOT), Chennai, is gratefully acknowledged for the deployment and maintenance of OMNI buoy. A. Mukherjee provided the wavelet code for calculating rotary spectra. Figures in this manuscript are generated using FERRET. This is INCOIS contribution Number 172.
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