The mechanism of the formation of the Indian Ocean dipole

A.B. Polonsky, A.V. Torbinskii, A.V. Gubarev

 Institute of Natural and Technical Systems, RF, Sevastopol, Lenin St., 28


DOI: 10.33075/2220-5861-2021-3-5-14

UDC 551.465


   The aim of this work is to study the impact of the instability of the system of zonal currents on the generation of the Indian Ocean dipole (IOD). For that, the cases of a critical layer occurrence in the southern part of the equatorial-tropical zone of the Indian Ocean within certain months for the period 1979–2018 are identified. In this layer, the phase velocity of neutral waves is equal to the average velocity of zonal currents, and the generation of unstable growing disturbances is most probable.

   In the work, the operative reanalysis ORAS5 data of European Centre for Medium-Range Weather Forecasts (ECMWF) on vertical distribution of potential temperature, salinity, and the zonal component of the current velocity for the period 1979 – 2018 were used. Monthly profiles of potential temperature, salinity, and the zonal component of the current velocity were selected from the ORAS5 array for the sections situated between 7.5 – 15.5°S, 50 – 100°E. By these data for each month, using the standard theory of planetary waves, the phase velocity of the lowest baroclinic mode of the Rossby long waves was calculated and the critical layer was determined. For each critical layer, its length was determined. The obtained time series of the critical layer length were compared to the variability of dipole mode index (DMI).

   It is shown that most cases of the critical layer occurrence take place in spring, one or two months before the onset of the positive IOD events. This indicates that the presence of instability in the system of the zonal currents can be a reason of the generation of IOD and the asymmetry of the amplitude of the dipole mode index between positive and negative events.

Keywords: Indian Ocean dipole, system of zonal currents, Rossby wave, critical layer.

To quote:

Full text in PDF(RUS)


  1. Saji N.H., Goswami B.N., Vinayachandran P.N., and Yamagata T. A dipole mode in the tropical Indian Ocean. Nature, 1999, No.401 (6751), pp. 360–363. DOI: 10.1038/43854
  2. Vinayachandran P.N., Lizuka S., and Yamagata T. Indian Ocean dipole mode events in an ocean general circulation model. Deep Sea Res, 2002, Part II, No. 49 (7), pp. 1573–1596. DOI:10.1016/S0967-0645(01)00157-6.
  3. / (data obrashcheniya: 05.08.2021).
  4. Saji N.H., and Yamagata T. Structure of SST and Surface Wind Variability during Indian Ocean Dipole Mode Events: COADS Observations. J. Clim., 2003, No. 16(16), pp. 2735–2751. DOI:10.1175/1520-0442(2003)016<2735:SOSASW>2.0.CO;2.
  5. Rao S.A., and Behera S.K. Subsurface influence on SST in the tropical Indian Ocean: structure and Interannual variability. Dyn. Atmos. Ocean, 2005, No. 39 (1), pp. 103–35. DOI:10.1016/j.dnatmoce.2004.10.014.
  6. Conway D., Allison E.H., Felstead R., and Goulden M. Rainfall variability in East Africa: implications for natural resources management and livelihoods. Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences, 2005, No. 363(1826), pp. 49–54. DOI: 10.1098/rsta.2004.1475.
  7. Page S.E., Siegert F., Rieley J., Boehm H.V., Jaya A., and Limin S. The amount of carbon released from peat and forest fires in Indonesia during 1997. Nature, 2002, No. 420 (6911), pp. 61–65. DOI: 10.1038/nature01131
  8. Kunii O., Kanagawa S., Yajima I., Hisamatsu Y., Yamamura S., Amagai T., and Ismail I.S. The 1997 haze disaster in Indonesia: its air quality and health effects. Archives of Environmental Health: An International Journal, 2002, No. 57 (1), pp. 16–22. DOI: 10.1080/00039890209602912
  9. Ummenhofer C.C., England M.H., McIntosh P.C., Meyers G.M., Pook M.J., Risbey J.S., Gupta A.S., and Taschetto A.S. What causes southeast Australia’s worst droughts? Geophysical Research Letters, 2009, No. 36 (4).
  10. Wang G., and Cai W. Two-year consecutive concurrences of positive Indian Ocean Dipole and Central Pacific El Niño preconditioned the 2019/2020 Australian “black summer” bushfires. Geoscience Letters, 2020, No. 7(1), pp. 1–9. DOI:10.1186/s40562-020-00168-2
  11. Polonskij A.B., Torbinskij A.V., and Basharin D.V. Vliyanie Severo-Atlanticheskogo kolebaniya, El’-Nin’o–Yuzhnogo kolebaniya i Indookeanskogo dipolya na prostranstvenno-vremennuyu izmenchivost’ prizemnoj temperatury vozduha i atmosfernogo davleniya Sredizemnomorsko-Chernomorskogo regiona (The influence of North Atlantic oscillation, El-Nino/Southern oscillation and Indian dipole on spatial-temporal variability of the surface air temperature and pressure over Mediterranean-Black Sea region). Vestnik Odesskogo gosudarstvennogo ekologicheskogo universiteta, 2008, No. 6, pp. 181–197.
  12. Polonskij A.B. Otklik v polyah prizemnoj temperatury vozduha, davleniya i osadkov Evrazijskogo regiona na anomalii temperatury poverhnosti okeana, svyazannye s Indookeanskim dipole (Response in the eurasian surface temperature, pressure and precipitation of the Indo-Ocean dipole). Monitoring systems of environment, 2018, No. 11(31), pp. 83–89. DOI: 10.33075/2220-5861-2018-1-83-89
  13. Rao S.A., Behera S.K., Masumoto Y., and Yamagata T. Interannual variability in the subsurface Indian Ocean with a special emphasis on the Indian Ocean Dipole. Deep Sea Res., 2002, Part II, No. 49(7), pp. 1549–1572. DOI: 10.1016/S0967-0645(01)00158-8
  14. Wang H., Murtugudde R., and Kumar A. Evolution of Indian Ocean dipole and its forcing mechanisms in the absence of ENSO. Climate Dynamics, 2016, No. 47(7), pp. 2481–2500. DOI: 10.1007/s00382-016-2977-y
  15. Philander S.G. El Nina, La Nina, and the Southern Oscillation. Academic Press: San Diego, USA, 1989, 293 p.
  16. Polonskij A.B., and Torbinskij A.V. Kriticheskij sloj v ekvatorial’no-tropicheskoj zone i Indookeanskij dipol’ (Critical layer in the equatorial-tropical zone and the Indian Ocean dipole). Monitoring systems of environment, 2019, No. 2 (36), pp. 88–92. DOI: 10.33075/2220-5861-2019-2-88-92
  17. Polonskij A.B., Torbinskij A.V., and Gubarev A.V. Identifikacziya mekhanizmov formirovaniya Indookeanskogo dipolya (Identification of formation mechanisms of Indian Ocean dipole). Monitoring systems of environment, 2020,  No. 2 (40), pp. 13–18. DOI: 10.33075/2220-5861-2020-2-13-18