This study examines the effect of surface current in the bulk formula for the wind stress, referred to as the relative wind (RW) effect, on the energetics of the geostrophic circulation and the upper ocean stratification in the Bay of Bengal (BoB) during the summer monsoon seasons. When the RW effect is taken into account in the high-resolution SCOAR (WRF-ROMS) regional coupled model simulation and compared to the run without such a consideration, the kinetic energy both in the mean (MKE) and eddy (EKE) is reduced by more than a factor of two. The most significant reduction in the kinetic energy is found along the path of the northward East India Coastal Current (EICC) and to the south of its separated latitude. The energetics calculations and spectral analysis reveal that this significant damping of EKE is primarily due to reduced eddy wind work principally at wavelengths close to the first baroclinic Rossby deformation radius, indicating the modulation of the wind work by geostrophic mesoscale eddy fields. Moreover, the mixed layer depth (MLD) is significantly shoaled south of the separated EICC latitude, the area dominated by anticyclonic eddy activity. The shallower mixed layer and enhanced stratification with the RW effect are attributed to doming of the isopycnals by the anomalous upward Ekman velocity, which itself is generated by the interaction of anticyclonic mesoscale surface current and the prevailing southwesterly monsoonal wind. Overall, the geostrophic circulation and upper ocean stratification along the EICC and south of its separated latitude exhibit the most significant dynamical response. This result implies that this southwestern part of the BoB is a hot spot for the momentum exchange between the surface circulation and the monsoonal winds, thus a potential area for focused field measurements for the ocean circulation energetics and air-sea interaction.
|Journal||Deep-Sea Research Part II: Topical Studies in Oceanography|
|Publication status||Published - 2019 Oct|
Bibliographical noteFunding Information:
H. Seo is grateful for support by ONR ( N00014-15-1-2588 and N00014-17-1-2398 ) and NOAA ( NA15OAR4310176 and NA17OAR4310255 ). A. Subramanian acknowledges the support by ONR ( N00014-17-S-B001 ). H. Song is supported by Yonsei University Research Fund ( 2018-22-0053 ) and National Research Foundation of Korea (NRF) grant funded by Korea government (MSIST) (NRF- 2019R1C1C1003663 ). J. Chowdary thanks ESSO-IITM and MoES for support. The computing resources were provided by the WHOI High-Performance Computing Facility ( https://whoi-it.whoi.edu/resources/ ). Authors are grateful for river discharge data provided by Dr. Fabrice Papa (LEGOS-IRD). HS also thanks Dr. Sudip Jana (MIT) for his constructive discussions and suggestions, which helped to improve the model simulations and interpretation of the results. Finally, the authors thank the anonymous reviewers for their constructive comments, which helped to substantially improve the manuscript.
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