Theoretical and Applied Climatology

, Volume 126, Issue 1–2, pp 285–301 | Cite as

Interannual variability of upper ocean stratification in Bay of Bengal: observational and modeling aspects

  • T. S. Fousiya
  • Anant Parekh
  • C. Gnanaseelan
Original Paper


The annual cycle and interannual variability of stratification in Bay of Bengal (BoB) are studied using both observations and Global Ocean Data Assimilation System (GODAS) analysis during 2003–2012. Annual cycle of stratification and sea surface temperature (SST) evolve coherently, highlighting its role on modulating air-sea interaction over this climatologically important region. Spatial distribution of stratification shows strong seasonality in ARGO observations, whereas it is highly underestimated in GODAS with highest discrepancies during fall and spring. The annual cycle of sea surface salinity (SSS) in GODAS is out of phase with observations implying potential feedbacks. During La Niña years, SSS drop in fall and winter and are lesser than those reported during El Niño years. All these features are misrepresented in GODAS. As stratification modulates air-sea interaction over BoB especially during El Niño and La Niña years, such misrepresentation of ocean stratification may lead to unrealistic thermocline-SST coupling in the models. The mean stratification and its interannual variability in GODAS are weaker than observed even though interannual variability in freshwater flux (P-E) is higher in GODAS. Detailed analysis of GODAS with in situ observations reveals that upper ocean current shear (vertical) is overestimated in GODAS, leading to unrealistically strong mixing which is primarily responsible for the deeper penetration of surface warm and freshwater resulting weaker stratification. As GODAS is used to initialize the ocean component of the coupled forecasting system for seasonal prediction of Asian monsoon, proper representation of stratification is essential. This study advocates the need of accurate representation of upper ocean salinity in GODAS for improved stratification. We speculate that improved stratification and mixing in the BoB improve summer monsoon forecast.


Indian Ocean Dipole Argo Freshwater Flux Global Ocean Data Assimilation System Precipitation Minus Evaporation 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



The authors acknowledge Director, IITM, for encouragement and support. FTS acknowledges the Council of Scientific and Industrial Research (CSIR), India, for the research fellowship. Authors thank INCOIS for providing ARGO as well as INCOIS-GODAS data ( and Coriolis ( for providing ARGO data and NIOT ( for providing in situ observations for this research. GODAS data is provided by the NOAA/OAR/ESRL PSD, Boulder, CO, USA, from their Web site at We also acknowledge various agencies for different data sets used in the study. The figures are prepared using Ferret. The comments from the reviewers have helped us to improve the manuscript.


  1. Adler RF, Huffman GJ, Chang A, Ferraro R, Xie P, Janowiak J, Rudolf B, Schneider U, Curtis S, Bolvin D, Gruber A, Susskind J, Arkin P, Nelkin E (2003) The version 2 Global Precipitation Climatology Project (GPCP) monthly precipitation analysis (1979-present). J Hydrometeorol 4:1147–1167CrossRefGoogle Scholar
  2. Agarwal N, Sharma R, Parekh A, Basu S, Sarkar A, Agarwal VK (2012) Argo observations of barrier layer in the tropical Indian Ocean. Adv Space Res 50:642–654. doi: 10.1016/j.asr.2012.05.021 CrossRefGoogle Scholar
  3. Akhil VP, Durand F, Lengaigne M, Vialard J, Keerthi MG, Gopalakrishna VV, Deltel C, Papa F, de Boyer Montégut C (2014) A modeling study of the processes of surface salinity seasonal cycle in the Bay of Bengal. J Geophys Res Oceans 119(6):3926–3947CrossRefGoogle Scholar
  4. Ali MM, Jagadeessh PSV, Jain S (2007) Effects of eddies and dynamic topography on the Bay of Bengal cyclone intensity. EOS Trans Am Geophys Union 88:93–95CrossRefGoogle Scholar
  5. Argo Science Team (1998) On the design and implementation of Argo—an initial plan for a global array of profiling floats, ICPO Report no. 21, GODAE Report no 5, 32 pp, The GODAE international project office, Melbourne, AustraliaGoogle Scholar
  6. Behringer DW, and Xue Y (2004) Evaluation of the global ocean data assimilation system at NCEP: The Pacific Ocean. Eighth symposium on integrated observing and assimilation systems for atmosphere, oceans, and land surface, AMS 84th annual meeting, Washington State Convention and Trade Center, Seattle, Washington, 11–15Google Scholar
  7. Benshila R, Durand F, Masson S, Bourdallé-Badie R, de Boyer Montégut C, Papa F, Madec G (2014) The upper Bay of Bengal salinity structure in a high-resolution model. Ocean Model 74:36–52, CrossRefGoogle Scholar
  8. Bhaskar U, TVS and Ravichandran M, and Devender R (2007) An operational objective analysis system at INCOIS for generation of Argo Value Added Products. Report no. INCOIS-MOG-ARGO-TR-04-2007. Indian National Centre for Ocean Information Services (INCOIS), Hyderabad, IndiaGoogle Scholar
  9. Chaitanya A, Durand F, Mathew S, Gopalakrishna V, Papa F, Lengaigne M, Vialard J, Kranthikumar C, Venkatesan R (2015) Observed year-to-year sea surface salinity variability in the Bay of Bengal during the 2009–2014 period. Ocean Dyn 65(2):173–186. doi: 10.1007/s10236-014-0802-x CrossRefGoogle Scholar
  10. Dave AC, Lozier MS (2013) Examining the global record of interannual variability in stratification and marine productivity in the low-latitude and mid-latitude ocean. J Geophys Res Oceans 118:3114–3127CrossRefGoogle Scholar
  11. Derber JC, Rosati A (1989) A global oceanic data assimilation system. J Phys Oceanogr 19:1333–1347CrossRefGoogle Scholar
  12. Doney SC (2006) Oceanography—plankton in a warmer world. Nature 444(7120):695–696CrossRefGoogle Scholar
  13. Felton CS, Bulusu S, Murty VSN (2013) ENSO-modulated cyclogenesis over the Bay of Bengal. J Clim 26:9806–9818CrossRefGoogle Scholar
  14. Girishkumar MS, Ravichandran M (2012) The influences of ENSO on tropical cyclone activity in the Bay of Bengal during October-December. Geophys Res Lett 117, C02033CrossRefGoogle Scholar
  15. Gopalakrishna VV, Murty VSN, Sengupta D, Shenoy S, Araligidad N (2002) Upper ocean stratification and circulation in the northern Bay of Bengal during the southwest monsoon of 1991. Cont Shelf Res 22:791–802CrossRefGoogle Scholar
  16. Han W, McCreary JP (2001) Modeling salinity distributions in the Indian Ocean. J Geophys Res 106:859–877CrossRefGoogle Scholar
  17. Han W, McCreary JP Jr, Kohler KE (2001) Influence of precipitation minus evaporation and Bay of Bengal Rivers on dynamics, thermodynamics, and mixed layer physics in the upper Indian Ocean. J Geophys Res 106(C4):6895–6916CrossRefGoogle Scholar
  18. Harenduprakash LL, Mitra AK (1988) Vertical turbulent mass flux below the sea surface and air-sea interaction: monsoon region of the Indian Ocean. Deep-Sea Res I 43:1423–1451Google Scholar
  19. Howden SD, Murtugudde R (2001) Effects of river inputs into the Bay of Bengal. J Geophys Res 106(19):825–19,843Google Scholar
  20. Huang B, Xue Y, Behringer DW (2008) Impacts of Argo salinity in NCEP Global Ocean Data Assimilation System: the tropical Indian Ocean. J Geophys Res 113, C08002. doi: 10.1029/2007JC004388 Google Scholar
  21. Jensen TG (2003) Cross-equatorial pathways of salt and tracers from the northern Indian Ocean: modelling results. Deep-Sea Res 2(50):2111–2128Google Scholar
  22. Kanamitsu MW, Ebisuzaki JW, Yang S-K, Hnilo JJ, Fiorino M, Potter GL (2002) NCEP-DEO AMIP-II reanalysis (R-2). Bull Am Meteorol Soc 83:1631–1643CrossRefGoogle Scholar
  23. Lakshmi V, Parekh A, Sarkar A (2009) Bimodal variation of SST and related physical processes over the north Indian Ocean: special emphasis on satellite observations. Int J Remote Sens 30:22CrossRefGoogle Scholar
  24. Locarnini RA, Mishonov AV, Antonov JI, Boyer TP, Garcia HE, Baranova OK, Zweng MM, Paver CR, Reagan JR, Johnson DR, Hamilton M and Seidov D (2013) World ocean atlas 2013, volume 1: temperature. In: Levitus S, Mishonov A Technical (ed), NOAA Atlas NESDIS 73, pp40Google Scholar
  25. McPhaden MJ (2002) El Niño and La Niña: causes and global consequences. In: Munn T (ed) Encyclopedia of global environmental change. John Wiley, Chichester, U. K., pp 353–370Google Scholar
  26. Mooley DA, Parthasarathy B (1983) Variability of the Indian summer monsoon and tropical circulation features. Mon Weather Rev 3:967–978CrossRefGoogle Scholar
  27. Neetu S, Lengaigne M, Vincent EM, Vialard J, Madec G, Samson G, Ramesh Kumar MR, Durand F (2012) Influence of upper-ocean stratification on tropical cyclone-induced surface cooling in the Bay of Bengal. J Geophys Res 117, C12020CrossRefGoogle Scholar
  28. Nyadjro ES, Subrahmanyam B, Shriver JF (2011) Seasonal variability of salt transport during the Indian Ocean monsoons. J Geophys Res 116, C08036. doi: 10.1029/2011JC006993 CrossRefGoogle Scholar
  29. Pant V, Girishkumar MS, Udaya Bhaskar TVS, Ravichandran M, Papa F, Thangaprakash VP (2015) Observed interannual variability of near-surface salinity in the Bay of Bengal. J Geophys Res Oceans. doi: 10.1002/2014JC010340, 120 Google Scholar
  30. Papa F, Durand F, Rossow WB, Rahman A, Bala SK (2010) Satellite altimeter derived monthly discharge of the Ganga Brahmaputra River and its seasonal to interannual variations from 1993 to 2008. J Geophys Res 115, C12013. doi: 10.1029/2009JC006075 CrossRefGoogle Scholar
  31. Papa F, Bala SK, Kumar Pandey R, Durand F, Rahman A, Rossow WB (2012) G-B river discharge from Jason-2 radar altimetry; an update to the long-term satellite-derived estimates of continental freshwater forcing flux into the Bay of Bengal. J Geophys Res 117, C11021CrossRefGoogle Scholar
  32. Parekh A, Chowdhary JS, Sayantani O, Fousiya TS, Gnanaseelan C (2015) Tropical Indian Ocean surface salinity bias in climate forecasting system coupled models and the role of upper Ocean processes. Clim Dyn. doi: 10.1007/s00382-015-2709-8 Google Scholar
  33. Prakash S, Mahesh C, Gairola RM (2012) Observed relationship between surface freshwater flux and salinity in the north Indian Ocean. Atmos Ocean Sci Lett 5:163–169CrossRefGoogle Scholar
  34. Prasad TG (1997) Annual and seasonal mean buoyancy fluxes for the tropical Indian Ocean. Curr Sci 73(8):667–674Google Scholar
  35. Ravichandran M, Behringer D, Sivareddy S, Girishkumar MS, Chacko N, Harikumar R (2013) Evaluation of the global ocean data assimilation system at INCOIS: the tropical Indian Ocean. Ocean Model 69:123–135. doi: 10.1016/j.ocemod.2013.05.003
  36. Rao RR, Sivakumar R (2003) Seasonal variability of sea surface salinity and salt budget of the mixed layer of the north Indian Ocean. J Geophys Res 108(C1):3009. doi: 10.1029/2001JC000907 CrossRefGoogle Scholar
  37. Rao SA, Gopalakrishna VV, Shetye SR and Yamagata T (2002) Why were cool SST anomalies absent in the Bay of Bengal during the 1997 Indian ocean dipole event. Geophys Res Lett 29(11):1555. doi: 10.1029/2001GL014645
  38. Reynolds RW, Rayner NA, Smith TM, Stokes DC, Wang W (2002) An improved in situ and satellite SST analysis for climate. J Clim 15:1609–1625CrossRefGoogle Scholar
  39. Saha S et al (2006) The NCEP climate forecast system. J Clim 19:3483–3517CrossRefGoogle Scholar
  40. Saha S, Moorthi S, Wu X, Wang J, Nadiga S, Tripp P, Behringer D, Hou Y-T, Chuang H, Iredell M, Ek M, Meng J, Yang R, Peña Mendez M, van den Dool H, Zhang Q, Wang W, Chen M and Becker E (2014) The NCEP Climate Forecast System Version 2. J. Climate 27:2185–2208. doi: 10.1175/JCLI-D-12-00823.1
  41. Sahai AK, Sharmila S, Abhilash S, Chattopadhyay R, Borah N, Krishna RPM, Susmitha J, Roxy M, De S, Pattnaik S (2013) Simulation and extended range prediction of monsoon intraseasonal oscillations in NCEP CFS/GFS version 2 framework. Curr Sci 104:1394–1408Google Scholar
  42. Saji NH, Goswami BN, Vinayachandran PN, Yamagata T (1999) A dipole mode in the tropical Indian Ocean. Nature 401:360–363Google Scholar
  43. Sengupta D, Bharath Raj GN, Shenoi SSC (2006) Surface freshwater from Bay of Bengal runoff and Indonesian throughflow in the tropical Indian Ocean. Geophys Res Lett 33, L22609. doi: 10.1029/2006GL027573 CrossRefGoogle Scholar
  44. Sengupta D, Raj GNB, Anitha DS (2007) Cyclone-induced mixing does not cool SST in the post-monsoon north Bay of Bengal. Atmos Sci Lett 9:1–6CrossRefGoogle Scholar
  45. Seo H, Xie S-P, Murtugudde R, Jochum M, Miller AJ (2009) Seasonal effects of Indian Ocean freshwater forcing in a regional coupled model*. J Clim 22:6577–6596CrossRefGoogle Scholar
  46. Sharma R, Agarwal N, Basu S, Agarwal VK (2007) Impact of satellite-derived forcings on numerical ocean model simulations and study of Sea surface salinity variations in the Indian Ocean. J Clim 20:871–890CrossRefGoogle Scholar
  47. Shenoi SSC, Shankar D, Shetye SR (2002) Differences in heat budgets of the near surface Arabian Sea and Bay of Bengal: implications for the summer monsoon. J Geophys Res 107(C6):3052CrossRefGoogle Scholar
  48. Shetye SR, Gouveia AD, Shankar D, Shenoi SSC, Vinayachandran PN, Sundar D, Michael GS, Nampoothiri G (1996) Hydrography and circulation in the western Bay of Bengal during the northeast monsoon. J Geophys Res 101(C6):14,011–14,026CrossRefGoogle Scholar
  49. Sreenivas P, Chowdary JS, Gnanaseelan C (2012) Impact of tropical cyclones on the intensity and phase propagation of fall Wyrtki jets. Geophys Res Lett 39:L22603. doi: 10.1029/2012GL053974
  50. Sreenivas P, Gnanaseelan C (2014) Impact of oceanic processes on the life cycle of severe cyclonic storm “Jal”. IEEE Geosci Remote Sens Lett. doi: 10.1109/LGRS.2013.2271512, 1–5 Google Scholar
  51. Thompson B, Gnanaseelan C, Salvekar PS (2006) Variability in the Indian Ocean circulation and salinity and its impact on SST anomalies during dipole events. J Mar Res 64:853–858CrossRefGoogle Scholar
  52. Varkey MJ, Murty VSN, Suryanarayana A (1996) Physical oceanography of the Bay of Bengal and Andaman Sea. Oceanogr Mar Biol 34:1–70Google Scholar
  53. Venkatesan R, Shamji VR, Latha G, Simi M, Rao RR, Muthiah A, Atmanand MA (2013) In situ ocean subsurface time-series measurements from OMNI buoy network in the Bay of Bengal. Curr Sci 104:1166–1177Google Scholar
  54. Vinayachandran PN, Nanjundiah RS (2009) Indian Ocean sea surface salinity variations in a coupled model. Clim Dyn 33:245–263CrossRefGoogle Scholar
  55. Vinayachandran PN, Murty VSN, Ramesh Babu V (2002) Observations of barrier layer formation in the Bay of Bengal during summer monsoon. J Geophys Res 107(C12):8018. doi: 10.1029/2001JC000831 CrossRefGoogle Scholar
  56. Webster PJ, Moore A, Loschnigg J and Leban M (1999) Coupled ocean-atmosphere dynamics in the Indian Ocean during 1997-98. Nature 401(23):356–360Google Scholar
  57. Yin X, Gruber A, Arkin P (2004) Comparison of the GPCP and CMAP Merged Gauge–Satellite Monthly Precipitation Products for the Period 1979–2001. J Hydrometeorol 5:1207–1222CrossRefGoogle Scholar
  58. Yu L, McPhaden MJ (2011) Ocean preconditioning of cyclone nargis in the Bay of Bengal: interaction between rossby waves, surface fresh waters, and Sea surface temperatures. J Phys Oceanogr 41:1741–1755CrossRefGoogle Scholar
  59. Yu L, Weller RA, Sun B (2004a) Improving latent and sensible heat flux estimates for the Atlantic Ocean (1988–1999) by a synthesis approach. J Clim 17:373–393CrossRefGoogle Scholar
  60. Yu L, Weller RA, Sun B (2004b) Mean and variability of the WHOI daily latent and sensible heat fluxes at in situ flux measurement sites in the Atlantic Ocean. J Clim 17:2096–2118CrossRefGoogle Scholar
  61. Zweng MM, Reagan JR, Antonov JI, Locarnini RA, Mishonov AV, Boyer TP, Garcia HE, Baranova OK, Johnson DR, Seidov D, Biddle MM (2013) World ocean atlas 2013, volume 2. In: Salinity S Levitus, A. Mishonov Technical (ed), NOAA Atlas NESDIS 74, pp 39Google Scholar

Copyright information

© Springer-Verlag Wien 2015

Authors and Affiliations

  1. 1.Indian Institute of Tropical MeteorologyPuneIndia

Personalised recommendations