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Seasonal variability of near-surface isothermal layer and thermocline characteristics of the Tropical Indian Ocean

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Summary

A subset of world ocean monthly mean temperature climatology generated by Levitus and Boyer (1994), is utilised to describe the observed seasonal variability of the characteristics of the near-surface isothermal layer and thermocline for the entire tropical Indian Ocean (TIO). The most salient features of the observed annual cycle are described in terms of amplitude and phase of the annual and semi-annual frequencies employing Fourier analysis technique. On the annual mode, the near-surface isothermal layer depth (ILD), exhibits larger variability away from the equator with peak values in the northernmost Arabian Sea, the northernmost Bay of Bengal and the southern TIO, while on the semi-annual mode, it shows larger variability in the central Arabian Sea. The variability of the near-surface isothermal layer temperature (ILT), on the annual mode, is very weak in the warmpool region, and increases with latitude, while on the semi-annual mode, it shows larger variability in the northwestern Arabian Sea. The variability of 20°C isotherm topography (D20), on the annual mode, is weakest in the equatorial region and largest in the coastal regions of the Arabian Sea and the Bay of Bengal and in the southern T10, while on the semi-annual mode, it is prominent in the eastern and western equatorial regions. The thermocline gradient (TG) is very sharp below the warmpool region and diffuses meridionally. On the annual mode, it shows larger variability in the southern TIO, off Somalia and northernmost Arabian Sea, while on the semiannual mode, it shows larger variability in the southwestern Arabian Sea and eastern equatorial Indian Ocean. The relationship between near-surface isothermal layer and thermocline characteristics over an annual cycle are explored through correlation analysis. The correlation between ILD and ILT is strong over much of the basin with the exception of the equatorial and coastal upwelling/downwelling zones where internal ocean dynamics are important. In the southern TIO, entrainment of colder waters appears to be important in maintaining the annual cycle of ILT as strong correlation is noticed between ILT and TG. In the Indo-Pacific throughflow region and another region west of it, the annual Rossby waves appear to control D20, as correlations between D20 and other fields are strong in these regions. A similar strong correlation between D20 and ILD is also noticed in the southeastern Arabian Sea where mode-2 Rossby waves identified in numerical model solutions.

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References

  • Bauer, S., Hitchcock, G. L., Olson, D. B., 1991: Influence of monsoonally forced Ekman dynamics upon surface layer depth and plankton biomass distribution in the Arabian Sea.Deep-Sea Res.,38(5), 531–553.

    Google Scholar 

  • Cane, M., 1980: On the dynamics of equatorial currents, with application to the Indian Ocean.Deep-Sea Res.,27A, 525–544.

    Google Scholar 

  • Colborn, J. G., 1975:The Thermal Structure of the Indian Ocean. Honolulu: University Press of Hawaii, 173pp (IIOE Oceanogr. Monogr., 2).

    Google Scholar 

  • Conkright, M. E., Levitus, S., Boyer, T. P., Bartolacci, D., Luther, M., 1994:Atlas of the Northern Indian Ocean. St Petersburg: Univ. of South Florida, 157pp.

    Google Scholar 

  • Cutler, A., Swallow, J., 1984: Surface currents of the Indian Ocean (to 25° S, 100° E) (compiled from archived historic data), Rept. No. 187, 8pp and 36 charts, Meterological Office, Institute of Oceanographic Sciences, Bracknell, UK.

    Google Scholar 

  • De, U. S., Joshi, K. S., 1995: Genesis of cyclonic disturbances over the north Indian Ocean 1891–1990. India Meteorological Department Pre-Published Scientific Report No. 1995/3, 47 pp.

  • Duing, J. W., Leetma, A., 1980: Arabian Sea cooling: A preliminary heat budget.J. Phys. Oceangr.,10, 307–312.

    Google Scholar 

  • Godfrey, J. S., Alexiou, A., Ilahude, A. G., Legler, D. M., Luther, M. E., McCreary, J. P., Meyers, G. A., Mizuno, K., Rao, R. R., Shetye, S. R., Toole, J. H., Wacongne, S., 1995: The Role of the Indian Ocean in the Global Climate System: Recommendations Regarding the Global Ocean Observing System. Report of the Ocean Observing System Development Panel, Texas A and M University, College Station, TX, USA, 89pp.

    Google Scholar 

  • Hastenrath, S., Greischar, L. L., 1989:Climatic Atlas of the Indian Ocean, Part III: Upper Ocean Structure. Madison, WI: The University fo Wisconsin Press, 26pp and 247 charts.

    Google Scholar 

  • India Meteorological Department, 1979: Tracks of Storms and Depressions in the Bay of Bengal and Arabian Sea (1877–1970). New Delhi, India; 26 pp & 186 maps.

  • Jenkins, G. M., Watts, D. G., 1968:Spectral Analysis And its Applications. Holden-Day, 525pp.

  • Jensen, R. G., 1991: Modelling the seasonal undercurrents in the Somali current system.J. Geophys. Res.,96(C12), 22151–22167.

    Google Scholar 

  • Ji, M., Leetma, A., Derber, J., 1995: An ocean analysis system for seasonal and interannual climate studies.Mon. Wea. Rev.,123, 460–481.

    Google Scholar 

  • Krishnamurti, T. N., Oosterhof, D. K., Mehta, A. V., 1988: Air-sea interaction on the time scale of 30–50 days.J. Atmos. Sci.,45, 1304–1322.

    Google Scholar 

  • Levitus, S., 1982: Climatological Atlas of the World Ocean. NOAA Prof. Paper 13, US Government Printing Office, Washington DC, 173pp.

    Google Scholar 

  • Levitus, S., Boyer, T. P., 1994: World Ocean Atlas 1994: Volume 4: Temperature, NOAA Atlas NEDIS 4, US Dept. of Commerce, Washington DC, USA, 117pp.

    Google Scholar 

  • McCreary, J. P., Kundu, P. J., Molinari, R. L., 1993: A numerical investigation of dynamics, thermodynamics and mixed layer processes in the Indian Ocean.Progress in Oceanography,31(3), 181–244.

    Google Scholar 

  • McPhaden, M. J., 1982: Variability in the central equatorial Indian Ocean Part I: Ocean dynamics.J. Mar. Res.,40(1), 157–176.

    Google Scholar 

  • Mizuno, K., Peter, B. N., Watanabe, T., 1995: Observation on subsurface temperature by voluntary ships. Japanese Experiment on Asian Monsoon (JEXAM) Annual Report April 1994-March 1995, 41–59pp.

  • Molinari, R. L., Festa, J. F., Swallow, J. C., 1986a: Mixed layer and thermocline depth climatologies in the western Indian Ocean. NOAA Tech. Memor. ERL AOML-64, 40pp, Atlantic Oceangr. and Meteorol. Lab., Miami, FL.

    Google Scholar 

  • Molinari, R. L., Swallow, J. C., Festa, J. F., 1986b: Evolution of the near-surface thermal structure in the western Indian Ocean during FGGE, 1979.J. Mar. Res.,44, 739–762.

    Google Scholar 

  • Molinari, R. L., Olson, D., Reverdin, G., 1990: Surface current distributions in the tropical Indian Ocean derived from compilations of surface buoy trajectories.J. Geophys. Res.,95, (C5), 7217–7238.

    Google Scholar 

  • O'Brien, J. J., Hurlburt, H. E., 1974: Equatorial Jet in the Indian Ocean: Theory.Science,184, 1075–1077.

    Google Scholar 

  • Ocean Observing System Development Panel, 1995: Scientific Design for the Common Module of the Global Ocean Observing System and the Global Climate Observing System: An Ocean Observing System for Climate, Department of Oceanography, Texas A & M University, College Station, Texas, 265pp.

    Google Scholar 

  • Perigaud, C., Delecluse, P., 1992: Annual sea level variations in the southern tropical Indian Ocean from GEOSAT and shallow water simulations.J. Geophys. Res.,97(C12), 20, 169–20, 178.

    Google Scholar 

  • Prasanna Kumar, S., Unnikrishnan, A. S., 1995: Seasonal cycle of temperature and associated wave phenomena in the upper layers of the Bay of Bengal.J. Geophys. Res.,100(C7), 13585–13593.

    Google Scholar 

  • Quadfasel, D. R., 1982: Low frequency variability of the 20°C isotherm topography in the western equatorial Indian Ocean.J. Geophys. Res.,87, 1990–1996.

    Google Scholar 

  • Rao, R. R., 1986: Cooling and deepening of the mixed layer in the central Arabian Sea during MONSOON-77: Observations and simulations.Deep-Sea Res.,33(10), 1413–1424.

    Google Scholar 

  • Rao, R. R., 1987: Further analysis on the thermal response of the upper Bay of Bengal to the forcing of pre-monsoon cyclonic storm and summer monsoonal onset during MONEX-79.Mausam,38(2), 147–156.

    Google Scholar 

  • Rao, R. R., Molinari, R. L., Festa, J. F., 1989: Evolution of the climatological near-surface thermal structure of the tropical Indian Ocean I. Description of mean monthly mixed layer depth, sea surface temperature, surface current, and surface meteorological fields.J. Geophys. Res.,94(C8), 10,801–10,815.

    Google Scholar 

  • Rao, R. R., Molinari, R. L., Festa, J. F., 1991: Surface meteorological and subsurface oceanographic atlas of the tropical Indian Ocean. NOAA Tech. Memor. ERL-AOML-69, 59pp.

  • Rao, R. R., 1995a:Atlas of Surface Meteorology and Surface Oceanography of the Tropical Indian Ocean. Kochi: Naval Physical & Oceanographic Laboratory, 66pp.

    Google Scholar 

  • Rao, R. R., 1995b: Atlas of near-surface thermohaline fields of the tropical Indian Ocean from Levltus climatology, Kochi: Naval Physical & Oceanographic Laboratory, 147pp.

    Google Scholar 

  • Rao, R. R., Molinari, R. L., Festa, J. F., 1996a: Mixed layer dynamics of the tropical Indian Ocean, II Diagnostic estimates of mixed layer temperature (Manuscript under preparation).

  • Rao, R. R., Sivakumar, R., Ali, M. M., 1996b: A comparison of GEOSAT and modelled sea level data with heat content in the tropical Indian Ocean, (Manuscript under preparation).

  • Reverdin, G., 1985: Convergence in the Equatorial Surface Jets of the Indian Ocean.J. Geophys. Res.,90(C6), 11,741–11,750.

    Google Scholar 

  • Reverdin, G., 1987: The upper equatorial Indian ocean: The climatological seasonal cycle.J. Phys. Oceanogr.,7(8), 903–927.

    Google Scholar 

  • Robinson, M., Bauer, R., Schroeder, E., 1979: Atlas of North Atlantic-Indian Ocean Monthly Mean Temperatures and Mean Salinities of the Surface Layer, Naval Oceanographic Office, NOORP-18, NSTL Station, Bay St. Louis, Mississippi 39522, 234pp.

    Google Scholar 

  • Shetye, S. R., 1986: A model study of the seasonal cycle of the Arabian Sea surface temperature.J. Mar. Res.,44, 521–542.

    Google Scholar 

  • Sprintall, J., Tomczak, M., 1990: Salinity considerations in the oceanic surface mixed layer, Ocean Sciences Institute Report No. 36, The University of Sydney, 170pp.

  • Srinivasan, J., Gadgil, S., Webster, P. J., 1993: Meridional propagation of large scale monsoon convective zones.Meteorol. Atmos. Phys.,52, 15–35.

    Google Scholar 

  • Stramma, L., 1992: The South Indian ocean current.J. Phys. Oceanogr.,22, 421–430.

    Google Scholar 

  • Szabados, M., Bailey, R., Rual, P., Rebert, J. P., Ji, M., 1995: The TOGA XBT program: the use of upper ocean thermal data for analysis and prediction of climate variability. Abstracts of International Scientific Conference on Tropical Oceans Global Atmosphere. Melbourne, Australia, 116–117.

  • Vinayachandran, P. N., 1995: The Bay of Bengal circulation in an ocean general circulation model. Ph D Dissertation, 167pp

  • Woodberry, K. E., Luther, M. E., O'Brien, J. J., 1989: The wind driven seasonal circulation in the southern tropical Indian Ocean.J. Geophys. Res.,94(C12), 17,985–18,002.

    Google Scholar 

  • WOCE, 1993: Workshop on the use of sub-surface thermal data for climate studies. Brest, ITPO Report No. 9, WOCE Report No. 110/93, 60pp.

  • Wyrtki, K., 1971:Oceanographic Atlas of the International Indian Ocean Expedition. Washington DC: Natl. Sci. Found., 531pp.

    Google Scholar 

  • Wyrtki, K., 1973: An Equatorial Jet in the Indian Ocean.Science,181, 262–264.

    Google Scholar 

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  1. R. R. Rao & R. Sivakumar

    Present address: Naval Physical & Oceanographic Laboratory, 682021, Kochi, India

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    Rao, R.R., Sivakumar, R. Seasonal variability of near-surface isothermal layer and thermocline characteristics of the Tropical Indian Ocean. Meteorl. Atmos. Phys. 61, 201–212 (1996). https://doi.org/10.1007/BF01025705

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