Interannual variability and characteristics of the East India Coastal Current associated with Indian Ocean Dipole events using a high resolution regional ocean model
The characteristics and variability of the East India Coastal Current (EICC), the western boundary current in the Bay of Bengal (BoB) during the Indian Ocean Dipole (IOD) years between 2006 and 2012 have been investigated using the high-resolution Regional Ocean Modeling System (ROMS). The evolution of temperature, mixed layer depth (MLD), and seasonal basin scale circulation in the upper ocean simulated by the model agrees well with the observations. The EICC in BoB is characterized by a seasonal reversal flow: the poleward EICC during February−May and the equatorward EICC during August−December. A long-term simulation from 2006 to 2012 suggest that the circulation pattern, boundary current structure, and transport in the western BoB are completely different in positive and negative IOD years. As IOD is mainly phase-locked to the seasonal cycle with most significant influence in the Borel autumn, the equatorward EICC is affected during the IOD years. It is found that the strength of this EICC is ~ 5 Sv in October 2010 and a weaker EICC dominated by the presence of eddies is observed in October 2006. We also quantified the local and remote forcing effects on the variability of EICC and found that the seasonal coastal Kelvin waves (KWs) play a dominant role in the development of the EICC. During positive IOD year 2006, due the absence of second downwelling KW, the EICC is completely disorganized and dominated by the eddies, whereas in the negative IOD year 2010, the strong second downwelling KW plays a key role in developing organized and stable EICC in the western BoB.
KeywordsInterannual variability of EICC Bay of Bengal ROMS EICC transport IOD Seasonal Kelvin waves
The authors gratefully acknowledge http://www.myroms.org for providing online access of the ocean model ROMS. We have obtained wind, net heat flux, evaporation, and precipitation data from ECMWF Era-Interim. The temperature and salinity data required for model initialization are downloaded from MERCATOR Ocean Model. The satellite altimeter products used here were provided by Ssalto/Duacs and distributed by AVISO (ftp://ftp.aviso.oceanobs.com/), with support from CNES. DMI indices are available at http://www.jamstec.go.jp/frcgc/research/d1/iod/sstdmi.weekly.ascii. The ONI index is available at NOAA Climate pacific Center (http://www.cpc.ncep.noaa.gov/). The authors are thankful to the Indian Institute of Technology Kharagpur, India, for providing research fellowship and necessary facilities through MHRD for carrying out this research work. We would also like to thank for the financial support given by Indian National Centre for Ocean Information Services (INCOIS), SRIC/CMI project of IIT Kharagpur, and Ministry of Earth Sciences, Government of India, to conduct this research.
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