Indian Ocean Intraseasonal Variability in an Ocean General Circulation Model

A. Schiller CSIRO Marine Research, Hobart, Tasmania, Australia

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J. S. Godfrey CSIRO Marine Research, Hobart, Tasmania, Australia

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Abstract

The impact of atmospheric intraseasonal variability on the tropical Indian Ocean is examined with an ocean general circulation model (OGCM). The model is forced by observation-based wind stresses and surface heat fluxes from an atmospheric boundary layer model. Composites of 26 well-defined boreal spring and summer intraseasonal events from 1985 to 1994 are used to explore surface and subsurface impacts of intraseasonal oscillations in the ocean. The phase and amplitude of simulated intraseasonal sea surface temperature (SST) variations agree well with observations. The net surface heat flux dominates the composite mixed layer heat budget on intraseasonal timescales, while entrainment through the base of the mixed layer contributes locally. Horizontal advection is of secondary importance in the composite heat balance. However, inspection of individual events suggests that in individual intraseasonal events different processes may control their dynamics.

A characteristic feature of equatorial intraseasonal variability is the formation of a shallow mixed layer caused by a surface freshwater cap associated with strong freshwater fluxes into the ocean. This “barrier-layer” formation in association with mean temperature inversions significantly impacts the heat transfer across the bottom of the mixed layer during the transition from calm and clear to windy and cloudy conditions of an event, such that strong entrainment at the peak of an intraseasonal event warms rather than cools the surface.

The intraseasonal mixed layer salinity budget is about equally determined by entrainment, surface freshwater fluxes, and horizontal advection. The latter is due to notable horizontal salinity gradients in the central and eastern Indian Ocean in combination with equatorial jetlike velocity anomalies that develop in response to the intraseasonal atmospheric wind forcing.

Use of equatorial mooring data in 1994 was useful for understanding model phenomena on several timescales. However, the observations contained no representative intraseasonal events.

Corresponding author address: Dr. A. Schiller, CSIRO Marine Research, GPO Box 1538, Hobart, 7001, Tasmania, Australia. Email: andreas.schiller@csiro.au

Abstract

The impact of atmospheric intraseasonal variability on the tropical Indian Ocean is examined with an ocean general circulation model (OGCM). The model is forced by observation-based wind stresses and surface heat fluxes from an atmospheric boundary layer model. Composites of 26 well-defined boreal spring and summer intraseasonal events from 1985 to 1994 are used to explore surface and subsurface impacts of intraseasonal oscillations in the ocean. The phase and amplitude of simulated intraseasonal sea surface temperature (SST) variations agree well with observations. The net surface heat flux dominates the composite mixed layer heat budget on intraseasonal timescales, while entrainment through the base of the mixed layer contributes locally. Horizontal advection is of secondary importance in the composite heat balance. However, inspection of individual events suggests that in individual intraseasonal events different processes may control their dynamics.

A characteristic feature of equatorial intraseasonal variability is the formation of a shallow mixed layer caused by a surface freshwater cap associated with strong freshwater fluxes into the ocean. This “barrier-layer” formation in association with mean temperature inversions significantly impacts the heat transfer across the bottom of the mixed layer during the transition from calm and clear to windy and cloudy conditions of an event, such that strong entrainment at the peak of an intraseasonal event warms rather than cools the surface.

The intraseasonal mixed layer salinity budget is about equally determined by entrainment, surface freshwater fluxes, and horizontal advection. The latter is due to notable horizontal salinity gradients in the central and eastern Indian Ocean in combination with equatorial jetlike velocity anomalies that develop in response to the intraseasonal atmospheric wind forcing.

Use of equatorial mooring data in 1994 was useful for understanding model phenomena on several timescales. However, the observations contained no representative intraseasonal events.

Corresponding author address: Dr. A. Schiller, CSIRO Marine Research, GPO Box 1538, Hobart, 7001, Tasmania, Australia. Email: andreas.schiller@csiro.au

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  • Chen, D., A. J. Busalacchi, and L. M. Rothstein, 1994a: The roles of vertical mixing, solar radiation, and wind stress in a model simulation of the sea surface temperature seasonal cycle in the tropical Pacific Ocean. J. Geophys. Res., 99 , 2034520359.

    • Search Google Scholar
    • Export Citation
  • Chen, D., L. M. Rothstein, and A. J. Busalacchi, 1994b: A hybrid vertical mixing scheme and its application to tropical ocean models. J. Phys. Oceanogr., 24 , 21562179.

    • Search Google Scholar
    • Export Citation
  • Cronin, M. F., and M. J. McPhaden, 1997: The upper ocean heat balance in the western equatorial Pacific warm pool during September–December 1992. J. Geophys. Res., 102 , 85338553.

    • Search Google Scholar
    • Export Citation
  • Emanuel, K. A., 1987: An air–sea interaction model of intraseasonal oscillations in the tropics. J. Atmos. Sci., 44 , 23242340.

  • Feng, M., R. Lukas, P. Hacker, R. A. Weller, and S. P. Anderson, 2000: Upper-ocean heat and salt balances in the western equatorial Pacific in response to the intraseasonal oscillation during TOGA COARE. J. Climate, 13 , 24092427.

    • Search Google Scholar
    • Export Citation
  • Gadgil, S., P. V. Joseph, and N. V. Joshi, 1984: Ocean–atmosphere coupling over monsoon regions. Nature, 312 , 141143.

  • Godfrey, J. S., and A. Schiller, 1997: Tests of mixed layer schemes and surface boundary conditions in an ocean general circulation model, using an equatorial data set. CSIRO Rep. 231, 39 pp.

    • Search Google Scholar
    • Export Citation
  • Godfrey, J. S., E. F. Bradley, P. A. Coppin, L. F. Pender, T. J. McDougall, E. W. Schulz, and I. Helmond, 1999: Measurements of upper ocean heat and freshwater budgets near a drifting buoy in the equatorial Indian Ocean. J. Geophys. Res., 104 , 1326913302.

    • Search Google Scholar
    • Export Citation
  • Harrison, D. E., and G. A. Vecchi, 2001: January 1999 Indian Ocean cooling event. Geophys. Res. Lett., 28 , 3173720.

  • Hendon, H. H., 2000: Impact of air–sea coupling on the Madden–Julian oscillation in a general circulation model. J. Atmos. Sci., 57 , 39393952.

    • Search Google Scholar
    • Export Citation
  • Hendon, H. H., and J. Glick, 1997: Intraseasonal air–sea interaction in the tropical Indian and Pacific Oceans. J. Climate, 10 , 647661.

    • Search Google Scholar
    • Export Citation
  • Jones, C., D. E. Waliser, and C. Gautier, 1998: The influence of the Madden–Julian oscillation on ocean surface heat fluxes and sea surface temperature. J. Climate, 11 , 10571072.

    • Search Google Scholar
    • Export Citation
  • Kalnay, E,, and Coauthors. 1996: The NCEP/NCAR 40-Year Reanalysis Project. Bull. Amer. Meteor. Soc., 77 , 437471.

  • Kessler, W. S., and R. Kleeman, 2000: Rectification of the Madden–Julian oscillation into the ENSO cycle. J. Climate, 13 , 35603575.

    • Search Google Scholar
    • Export Citation
  • Kessler, W. S., M. J. McPhaden, and K. M. Weickmann, 1995: Forcing of intraseasonal Kelvin waves in the equatorial Pacific. J. Geophys. Res., 100 , 1061310631.

    • Search Google Scholar
    • Export Citation
  • Kleeman, R., and S. B. Power, 1995: A simple atmospheric model of surface heat flux for use in ocean modeling studies. J. Phys. Oceanogr., 25 , 92105.

    • Search Google Scholar
    • Export Citation
  • Kleeman, R., B. J. McAvaney, and R. C. Balgovind, 1993: An analysis of the interannual heat flux response in an atmospheric general circulation model. J. Geophys. Res., 99D , 55395550.

    • Search Google Scholar
    • Export Citation
  • Kleeman, R., R. A. Colman, N. R. Smith, and S. B. Power, 1996: A recent change in the mean state of the Pacific basin climate: Observational evidence and atmospheric and oceanic processes. J. Geophys. Res., 101 , 2048320499.

    • Search Google Scholar
    • Export Citation
  • Lau, K-M., and C-H. Sui, 1997: Mechanisms of short-term sea surface temperature regulation: Observations during TOGA COARE. J. Climate, 10 , 465472.

    • Search Google Scholar
    • Export Citation
  • Lawrence, D., and P. J. Webster, 2002: The boreal summer intraseasonal oscillation: Relationship between northward and eastward movement of convection. J. Atmos. Sci., 59 , 15931606.

    • Search Google Scholar
    • Export Citation
  • Legler, D. M., I. M. Navon, and J. J. O’Brien, 1989: Objective analysis of pseudostress over the Indian Ocean using a direct-minimization approach. Mon. Wea. Rev., 117 , 709720.

    • Search Google Scholar
    • Export Citation
  • Levitus, S., R. Burgett, and T. Boyer, 1994: World Ocean Atlas 1994, Salinity. Vol. 3, NOAA Atlas NESDIS 3, 99 pp.

  • Madden, R., and P. R. Julian, 1971: Detection of a 40–50 day oscillation in the zonal wind in the tropical Pacific. J. Atmos. Sci., 28 , 802708.

    • Search Google Scholar
    • Export Citation
  • Niiler, P. P., and E. B. Kraus, 1977: One-dimensional models of the upper ocean. Modeling and Prediction of the Upper Layers of the Ocean, E. B. Kraus, Ed., Pergamon, 143–172.

    • Search Google Scholar
    • Export Citation
  • Pacanowski, R. C., 1995: MOM2 documentation user’s guide and reference manual: Version 1.0. GFDL Tech. Rep. 3, 232 pp.

  • Pacanowski, R. C., and S. G. H. Philander, 1981: Parameterization of vertical mixing in numerical models of tropical oceans. J. Phys. Oceanogr., 11 , 14431451.

    • Search Google Scholar
    • Export Citation
  • Peters, H., M. C. Gregg, and J. M. Toole, 1988: On the parameterization of equatorial turbulence. J. Geophys. Res., 93 , 11991218.

  • Power, S. B., R. Kleeman, R. A. Colman, and B. J. McAvaney, 1995: Modeling the surface heat flux response to long-lived SST anomalies in the North Atlantic. J. Climate, 8 , 21612180.

    • Search Google Scholar
    • Export Citation
  • Premkumar, K., M. Ravichandran, S. R. Kalsi, D. Sengupta, and S. Gadgil, 2000: First results from a new observational system over the Indian seas. Curr. Sci., Indian Acad. Sci., 78 , 323330.

    • Search Google Scholar
    • Export Citation
  • Ralph, E. A., K. Bi, and P. P. Niiler, 1997: A Lagrangian description of the western equatorial Pacific response to the wind burst of December 1992. J. Climate, 10 , 17061721.

    • Search Google Scholar
    • Export Citation
  • Rao, R. R., R. L. Molinari, and J. F. Fiesta, 1989: Evolution of climatological near-surface thermal structure of the tropical Indian Ocean. 1. Description of mean monthly mixed layer depth, and sea surface temperature, surface currents and surface meteorological fields. J. Geophys. Res., 94 , 1080110815.

    • Search Google Scholar
    • Export Citation
  • Reppin, J., F. A. Schott, and J. Fischer, 1999: Equatorial currents and transports in the upper central Indian Ocean: Annual cycle and interannual variability. J. Geophys. Res., 104 , 1549515514.

    • Search Google Scholar
    • Export Citation
  • Reynolds, R. W., and T. M. Smith, 1994: Improved global sea surface temperature analyses using optimum interpolation. J. Climate, 7 , 929948.

    • Search Google Scholar
    • Export Citation
  • Schiller, A., 1999: How well does a coarse resolution circulation model simulate observed interannual variability in the upper Indian Ocean? Geophys. Res. Lett., 26 , 14851488.

    • Search Google Scholar
    • Export Citation
  • Schott, F., and J. P. McCreary, 2001: The monsoon circulation of the Indian Ocean. Progress in Oceanography, Vol. 51, Pergamon, 1–123.

    • Search Google Scholar
    • Export Citation
  • Sengupta, D., B. N. Goswami, and R. Senan, 2001a: Coherent intraseasonal oscillations of ocean and atmosphere during the Asian summer monsoon. Geophys. Res. Lett., 28 , 41274130.

    • Search Google Scholar
    • Export Citation
  • Sengupta, D., R. Senan, and B. N. Goswami, 2001b: Origin of intraseasonal variability of circulation in the tropical central Indian Ocean. Geophys. Res. Lett., 28 , 12671270.

    • Search Google Scholar
    • Export Citation
  • Shinoda, T., and R. Lukas, 1995: Lagrangian mixed layer modelling of the western equatorial Pacific. J. Geophys. Res., 100 , 25232541.

    • Search Google Scholar
    • Export Citation
  • Shinoda, T., and H. H. Hendon, 1998: Mixed layer modeling of intraseasonal variability in the tropical western Pacific and Indian Oceans. J. Climate, 11 , 26682685.

    • Search Google Scholar
    • Export Citation
  • Shinoda, T., and H. H. Hendon, 2001: Upper-ocean heat budget in response to the Madden–Julian oscillation in the western equatorial Pacific. J. Climate, 14 , 41474165.

    • Search Google Scholar
    • Export Citation
  • Shinoda, T., H. H. Hendon, and J. Glick, 1998: Intraseasonal variability of surface fluxes and sea surface temperature in the tropical western Pacific and Indian Oceans. J. Climate, 11 , 16851702.

    • Search Google Scholar
    • Export Citation
  • Slingo, J. M., D. P. Rowell, K. R. Sperber, and F. Nortley, 1999: On the predictability of the interannual behaviour of the Madden–Julian oscillation and its relationship to El Niño. Quart. J. Roy. Meteor. Soc., 125 , 583609.

    • Search Google Scholar
    • Export Citation
  • Sperber, K. R,, and Coauthors. 2001: Dynamical seasonal predictability of the Asian summer monsoon. Mon. Wea. Rev.,, 129 , 22262248.

  • Sprintall, J., and M. Tomczak, 1992: Evidence of the barrier layer in the surface layer of the tropics. J. Geophys. Res., 97 , 73057316.

    • Search Google Scholar
    • Export Citation
  • Stricherz, J., J. O’Brien, and D. Legler, 1992: Atlas of Florida State University Tropical Pacific Winds for TOGA 1966–1985. Florida State University, 256 pp.

    • Search Google Scholar
    • Export Citation
  • Vialard, J., and P. Delecluse, 1998: An OGCM study for the TOGA decade. Part II: Barrier-layer formation and variability. J. Phys. Oceanogr., 28 , 10891106.

    • Search Google Scholar
    • Export Citation
  • Waliser, D. E., K-M. Lau, and J. H. Kim, 1999: The influence of coupled sea surface temperatures on the Madden–Julian oscillation: A model perturbation experiment. J. Atmos. Sci., 56 , 333358.

    • Search Google Scholar
    • Export Citation
  • Webster, P. J., 2002: JASMINE: The scientific basis. Bull. Amer. Meteor. Soc.,, 83 , 16031630.

  • Webster, P. J., V. O. Magana, T. N. Palmer, J. Shukla, R. A. Thomas, M. Yanai, and T. Yasunari, 1998: Monsoons: Processes, predictability, and the prospects for prediction. J. Geophys. Res., 103 , 1445114510.

    • Search Google Scholar
    • Export Citation
  • Weller, R. A., and S. P. Anderson, 1996: Surface meteorology and air–sea fluxes in the western equatorial Pacific warm pool during the TOGA coupled ocean–atmosphere response experiment. J. Climate, 9 , 19591990.

    • Search Google Scholar
    • Export Citation
  • Wilson, S. G., 2000: How ocean vertical mixing and accumulation of warm surface water influence the “sharpness” of the equatorial thermocline. J. Climate, 13 , 36383656.

    • Search Google Scholar
    • Export Citation
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