Oceanography The Official Magazine of
The Oceanography Society
Volume 29 Issue 02

View Issue TOC
Volume 29, No. 2
Pages 112 - 123

OpenAccess

Observations of Currents Over the Deep Southern Bay of Bengal—With a Little Luck

By Hemantha W. Wijesekera , William J. Teague, Ewa Jarosz, David W. Wang, Tommy G. Jensen, S.U.P. Jinadasa , Harindra J.S. Fernando , Luca R. Centurioni , Zachariah R. Hallock , Emily L. Shroyer , and James N. Moum 
Jump to
Article Abstract Citation References Copyright & Usage
Article Abstract

Long-term time series of velocity, hydrographic, and turbulence fields were collected from a six-element subsurface mooring array in the southern Bay of Bengal. The moorings, deployed in December 2013 and recovered in August 2015, were entangled with commercial fishing nets and lines, while top subsurface buoys ended up being serendipitously closer to the surface than planned. In spite of these unexpected events, almost all the sensors and data were recovered. The moorings provided currents between 6 m and 500 m depths from acoustic Doppler current profilers, supplemented by hydrographic data and turbulent dissipation rates at selected depths. The observations captured the summer and winter monsoon currents, eddies, and intraseasonal oscillations. Near-surface currents as large as 1.75 m s–1 were observed in July 2014. Currents stronger than 0.5 m s–1 were confined to the upper 200 m. Observations of currents, temperature, and sea surface height (SSH) fields revealed eddylike features with positive and negative SSH anomalies (~20 cm) moving westward at speeds of about 0.1 m s–1. Intraseasonal oscillations with periods of 30 to 90 days were strongest near the surface. For the duration of the deployment, root-mean-square velocity fluctuations were about 0.1 m s–1 near the surface but decayed with depth and became nearly uniform (~0.03–0.06 m s–1) below 100 m. 

Citation

Wijesekera, H.W., W.J. Teague, E. Jarosz, D.W. Wang, T.G. Jensen, S.U.P. Jinadasa, H.J.S. Fernando, L.R. Centurioni, Z.R. Hallock, E.L. Shroyer, and J.N. Moum. 2016. Observations of currents over the deep southern Bay of Bengal—with a little luck. Oceanography 29(2):112–123, https://doi.org/10.5670/oceanog.2016.44.

References
    Anderson, D.L.T., and P.B. Rowlands. 1976. The role of inertia-gravity and planetary waves in the response of a tropical ocean to the incidence of an equatorial Kelvin wave on a meridional boundary. Journal of Marine Research 34:295–312.
  1. Bhat, G.S., S. Gadgil, P.V. Harish Kumar, S.R. Kalsi, P. Madhusoodanan, V.S.N. Murty, C.V.K. Prasada Rao, V. Ramesh Babu, L.V.G. Rao, R.R. Rao, and others. 2001. BOBMEX: The Bay of Bengal Monsoon Experiment. Bulletin of the American the Meteorological Society 82:2,217–2,243, https://doi.org/10.1175/1520-0477(2001)082<2217:BTBOBM>2.3.CO;2.
  2. Cane, M.A., and E.S. Sarachik. 1976. Forced baroclinic ocean motions: Part 1. Linear equatorial unbounded case. Journal of Marine Research 34:629–665.
  3. Durand, F., D. Shankar, F. Birol, and S.S.C. Shenoi. 2009. Spatiotemporal structure of the East India Coastal Current from satellite altimetry. Journal of Geophysical Research 114, C02013, https://doi.org/10.1029/2008JC004807.
  4. Girishkumar, M.S., M. Ravichandran, and M.J. McPhaden. 2013. Temperature inversions and their influence on the mixed layer heat budget during the winters of 2006–2007 and 2007–2008 in the Bay of Bengal. Journal of Geophysical Research 118:2,426–2,437, https://doi.org/​10.1002/jgrc.20192.
  5. Girishkumar, M.S., M. Ravichandran, M.J. McPhaden, and R.R. Rao. 2011. Intraseasonal variability in barrier layer thickness in the south central Bay of Bengal. Journal of Geophysical Research 116, C03009, https://doi.org/10.1029/2010JC006657.
  6. Jensen, T.G. 2001. Arabian Sea and Bay of Bengal exchange of salt and tracers in an ocean model. Geophysical Research Letters 28(20):3,967–3,970, https://doi.org/10.1029/2001GL013422.
  7. Jensen, T.G. 2003. Cross-equatorial pathways of salt and tracers from the northern Indian Ocean: Modelling results. Deep Sea Research Part II 50(12–13):2,111–2,127, https://doi.org/10.1016/S0967-0645(03)00048-1.
  8. Kemball-Cook, S., and B. Wang. 2001. Equatorial waves and air–sea interaction in the boreal summer intraseasonal oscillation. Journal of Climate 14:2,923–2,942, https://doi.org/10.1175/​1520-0442(2001)014<2923:EWAASI>2.0.CO;2.
  9. Lucas, A.J., E.L. Shroyer, H.W. Wijesekera, H.J.S. Fernando, E. D’Asaro, M. Ravichandran, S.U.P. Jinadasa, D. Sengupta, J.A. MacKinnon, J.D. Nash, and others. 2014. Mixing to monsoons: Air-sea interactions in the Bay of Bengal. Eos, Transactions American Geophysical Union 95:269–276, https://doi.org/10.1002/2014EO300001.
  10. McCreary, J.P., W. Han, D. Shankar, and S.R. Shetye. 1996. Dynamics of the East India Coastal Current: Part 2. Numerical solutions. Journal of Geophysical Research 101:13,993-14,010, https://doi.org/​10.1029/96JC00560.
  11. McPhaden, M.J., G. Meyers, K. Ando, Y. Masumoto, V.S.N. Murty, M. Ravichandran, F. Syamsudin, J. Vialard, L. Yu, and W. Yu. 2009. RAMA: The Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction. Bulletin of the American Meteorological Society 90:459–480, https://doi.org/10.1175/2008BAMS2608.1.
  12. Moum, J.N., and J.D. Nash. 2009. Mixing measurements on an equatorial ocean mooring. Journal of Atmospheric and Oceanic Technology 26:317–336, https://doi.org/10.1175/2008JTECHO617.1.
  13. Mukherjee, A., D. Shankar, V. Fernando, P. Amol, S.G. Aparna, R. Fernandes, G.S. Michael, S.T. Khalap, N.P. Satelkar, Y. Agarvadekar, and others. 2014. Observed seasonal and intraseasonal variability of the East India Coastal Current on the continental slope. Journal of Earth System Science 123(6):1,197–1,232, https://doi.org/10.1007/s12040-014-0471-7.
  14. Murty, V.S.N, Y.V.B. Sarma, and D.P. Rao. 1996. Variability of the oceanic boundary layer characteristics in the northern Bay of Bengal during MONTBLEX-90. Proceedings Indian Academy of Science (Earth Planet Science) 105:41–61, https://doi.org/10.1007/BF02880758.
  15. Murty, V.S.N., Y.V.B. Sarma, D.P. Rao, and C.S. Murty. 1992. Water characteristics, mixing and circulation in the Bay of Bengal during southwest monsoon. Journal of Marine Research 50:207–228.
  16. Perlin, A., and J.N. Moum. 2012. Comparison of thermal dissipation rate estimates from moored and profiling instruments at the equator. Journal of Atmospheric and Oceanic Technology, 29:1,347–1,362, https://doi.org/​10.1175/JTECH-D-12-00019.1. 
  17. Philander, S.G.H. 1990. El Niño, La Niña and the Southern Oscillation. Academic Press, 289 pp.
  18. Potemra, J.T., M.E. Luther, and J.J. O’Brien. 1991. The seasonal circulation of the upper ocean in the Bay of Bengal. Journal of Geophysical Research 96:12,667–12,683, https://doi.org/​10.1029/91JC01045.
  19. Rao, R.R., M.S. Girish Kumar, M. Ravichandran, A.R. Rao, V.V. Gopalakrishna, and P. Thadathil. 2010. Interannual variability of Kelvin wave propagation in the wave guides of the equatorial Indian Ocean, the coastal Bay of Bengal and the southeastern Arabian Sea during 1993–2006. Deep Sea Research Part I 57(1):1–13, https://doi.org/10.1016/​j.dsr.2009.10.008.
  20. Rao, R.R., and R. Sivakumar. 2003. Seasonal variability of sea surface salinity and salt budget of the mixed layer of the north Indian Ocean. Journal of Geophysical Research 108(C1), 3009, https://doi.org/10.1029/2001JC000907. 
  21. Rao, S.A., S.K. Saha, S. Pokhrel, D. Sundar, A.R. Dhakate, S. Mahapatra, S. Ali, H.S. Chaudhari, P. Shreeram, S. Vasimalla, and others. 2011. Modulation of SST, SSS over northern Bay of Bengal on ISO time scale. Journal of Geophysical Research 116, C09026, https://doi.org/​10.1029/2010JC006804.
  22. Schott, F., and J.P. McCreary. 2001. The monsoon circulation of the Indian Ocean. Progress in Oceanography 51:1–123, https://doi.org/10.1016/S0079-6611(01)00083-0.
  23. Schott, F., J. Reppin, J. Fisher, and D. Quadfasel. 1994. Currents and transports of the Monsoon Current south of Sri Lanka. Journal of Geophysical Research 99(C12):25,127–25,141, https://doi.org/​10.1029/94JC02216.
  24. Shankar, D., P.N. Vinayachandran, and A.S. Unnikrishnan. 2002. The monsoon currents in the north Indian Ocean. Progress in Oceanography 52:63–120, https://doi.org/10.1016/S0079-6611(02)00024-1. 
  25. Shenoi, S.S.C., D. Shankar, and S.R. Shetye. 2002. Differences in heat budgets of the near-surface Arabian Sea and Bay of Bengal: Implications for the summer monsoon. Journal of Geophysical Research 107(C6), 3052, https://doi.org/​10.1029/2000JC000679.
  26. Shetye, S.R., A.D. Gouveia, D. Shankar, S.S.C. Shenot, P.N. Vinayachandran, D. Sundar, G.S. Michael, and G. Nampoothiri. 1996. Hydrography and circulation in the western Bay of Bengal during the northeast monsoon. Journal of Geophysical Research 101:14,011–14,025, https://doi.org/​10.1029/95JC03307.
  27. Subrahmanyam, S., I.S. Robinson, J.R. Blundell, and P.G. Challenor. 2001. Indian Ocean Rossby waves observed in TOPEX/POSEIDON altimeter data and in model simulations. International Journal of Remote Sensing 22:1,141–1,167, https://doi.org/10.1080/014311601750038893.
  28. Suresh, I., J. Vialard, M. Lengaigne, W. Han, J. McCreary, F. Durand, and P.M. Muraleedharan. 2013. Origins of wind-driven intraseasonal sea level variations in the North Indian Ocean coastal waveguide. Geophysical Research Letters 40:5,740–5,744, https://doi.org/​10.1002/2013GL058312.
  29. Vialard, J., S.S.C. Shenoi, J.P. McCreary, D. Shankar, F. Durand, V. Fernando, and S.R. Shetye. 2009. Intraseasonal response of the northern Indian Ocean coastal waveguide to the Madden–Julian Oscillation. Geophysical Research Letters 36, L14606, https://doi.org/10.1029/2009GL038450.
  30. Vinayachandran, P.N., Y. Masurnoto, T. Mikawa, and T. Yarnagata. 1999. Intrusion of the Southwest Monsoon Current into the Bay of Bengal. Journal of Geophysical Research 104:11,077–11,085, https://doi.org/10.1029/1999JC900035.
  31. Vinayachandran, P.N., D. Shankar, S. Vernekar, K.K. Sandeep, P. Amol, C.P. Neema, and A. Chatterjee. 2013. A summer monsoon pump to keep the Bay of Bengal salty. Geophysical Research Letters 40:1,777–1,782, https://doi.org/​10.1002/grl.50274.
  32. Vinayachandran, P.N., and T. Yarnagata. 1998. Monsoon response of the sea around Sri Lanka: Generation of thermal domes and anticyclonic vorticies. Journal of Physical Oceanography 28:1,946–1,960, https://doi.org/10.1175/1520-0485(1998)028​<1946:MROTSA>2.0.CO;2.
  33. Webster, P.J., E.F. Bradley, C.W. Fairall, J.S. Godfrey, P. Hacker, R.A. Houze Jr., R. Lukas, Y. Serra, J.M. Hummon, T.D.M. Lawrence, and others. 2002. The JASMINE Pilot Study. Bulletin of the American Meteorological Society 83:1,603–1,630, https://doi.org/10.1175/BAMS-83-11-1603.
  34. Wijesekera, H.W., T.G. Jensen, E. Jarosz, W.J. Teague, E.J. Metzger, D.W. Wang, U. Jinadasa, K. Arulananthan, L. Centurioni, and H.J.S. Fernando. 2015. Southern Bay of Bengal currents and salinity intrusions during a fall monsoon transition. Journal of Geophysical Research 120(10):6,897–6,913, https://doi.org/10.1002/2015JC010744.
  35. Wijesekera, H.W., E. Shroyer, A. Tandon, M. Ravichandran, D. Sengupta, S.U.P. Jinadasa, H.J.S. Fernando, N. Agarwal, K. Arulanathan, G.S. Bhat, and others. In press. ASIRI: An ocean-​atmosphere initiative for Bay of Bengal. Bulletin of the American Meteorological Society, https://doi.org/10.1175/BAMS-D-14-00197.1.
  36. Wyrtki, K. 1973. An equatorial jet in the Indian Ocean. Science 181:262–264, https://doi.org/10.1126/science.181.4096.262.
  37. Yu., L., 2003. Variability of the depth of the 20°C isotherm along 6°N in the BoB: Its response to remote and local forcing and its relation to satellite SSH variability. Deep Sea Research Part II 50:2,285–2,304, https://doi.org/10.1016/S0967-0645(03)00057-2.
  38. Yu, L., and M.J. McPhaden. 2011. Ocean pre-conditioning of Cyclone Nargis in the Bay of Bengal: Interaction between Rossby waves, surface fresh waters, and sea surface temperatures. Journal of Physical Oceanography 41:1,741–1,755, https://doi.org/10.1175/2011JPO4437.1.
  39. Yu, L., J.J. O’Brien, and J. Yang. 1991. On the remote forcing of the circulation in the Bay of Bengal. Journal of Geophysical Research 96:20,449–20,454, https://doi.org/10.1029/91JC02424.
Copyright & Usage

This is an open access article made available under the terms of the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution, and reproduction in any medium or format as long as users cite the materials appropriately, provide a link to the Creative Commons license, and indicate the changes that were made to the original content. Images, animations, videos, or other third-party material used in articles are included in the Creative Commons license unless indicated otherwise in a credit line to the material. If the material is not included in the article’s Creative Commons license, users will need to obtain permission directly from the license holder to reproduce the material.