Critical layer in equatorial-tropical zone and Indian Ocean dipole

A.B. Polonsky1, 2, A.V. Torbinsky1

1Institute of Natural and Technical Systems, RF, Sevastopol, Lenin St., 28

E-mail: apolonsky5@mail.ru, uzundja@mail.ru

2Branch of Moscow State University in Sevastopol, RF, Sevastopol, Geroyev Sevastopol St., 7

DOI: 10.33075/2220-5861-2019-2-88-92

UDC 551.465

Abstract:

   The Indian Ocean dipole (IOD) is one of the main modes characterizing the interannual variability of the parameters of large-scale interaction of the ocean and the atmosphere in the equatorial zone of the World Ocean.

   The dipole is characterized as antiphase interannual variability of characteristics of the interaction of the ocean and the atmosphere in the western and eastern parts of the equatorial zone of the Indian Ocean. IOD may occur due to the climate change in the Pacific Ocean or develop independently due to the local interaction of the ocean and the atmosphere.

   It was hypothesized that the generation of growing disturbances, without the El Nino – Southern Oscillation (ENSO) events, is possible due to the instability of the systems of zonal currents and the absorption of wave energy in the critical layer. In this layer, the phase velocity of the Rossby waves is equal to the average velocity of the zonal currents.

   In this article the features of the formation of the critical layer in the equatorial-tropical zone of the Indian Ocean as well as months in which it appears are shown. Using this information allows explaining the mechanism of generating IOD events during ENSO events.

   In the work operative reanalysis data of European Centre for Medium-Range Weather Forecasts (ECMF) were used. Monthly profiles of potential temperature, salinity, and the zonal component of the velocity of currents were selected from the ORA-S3 array for the section with coordinates of 3–14°S, 72–74°E. For each month, the average potential density and average Brent – Väisälä frequency were calculated. The phase velocity of Rossby waves was calculated using monthly average Brent – Väisälä values. Next, a comparison was made of monthly average values ​​of the phase velocity of planetary waves with average values ​​of the velocities of the zonal currents.

   The results obtained allow us to conclude that, in the period from May to November, a critical layer is formed in the vicinity of 13° S and 72–74°E, in which the phase velocity of the Rossby waves is equal to the average velocity of the zonal currents. In this layer, in the given period of the year, due to the instability of the zonal currents, generation of growing perturbations, which are the internal Indian Ocean mode not related to ENSO, is possible

Keywords: Indian Ocean dipole, critical layer, interaction between the Indian Ocean dipole events and El-Niño events of different types.

Full text in PDF(RUS)

LIST OF REFERENCES:

  1. Coupled ocean–atmosphere dynamics in the Indian Ocean during 1997–98 / P.J. Webster, A.M. Moore, J.P. Loschnigg [et al.] // Nature, 401. P. 356–360
  2. A dipole mode in the tropical Indian Ocean / N.H. Saji, B.N. Goswami, P.N. Vinayachandran [et al.] // Nature. 1999.  401.  P. 360–363.
  3. Rao S.A., Behera S.K. Subsurface influence on SST in the tropical Indian Ocean: structure and Interannual variability // Dyn. Atmos. Ocean. 2005. № 39.  Р. 103–135.
  4. Paramount impact of the Indian Ocean dipole on the East African short rains: A CGCM study / S.K. Behera, J.J. Luo, S. Masson // J. Climate, 18.  P. 4514–4530.
  5. Polonsky A. B., Torbinsky A.V., Basharin D. V. Influence of the North Atlantic oscillation, El Nino-southern oscillation and the Indian Ocean dipole on the spatial and temporal variability of surface air temperature and atmospheric pressure in the Mediterranean-black sea region // Bulletin of the Odessa state ecological University. 2008. No. 6. P. 181-197.
  6. Polonsky A. B. Response in the fields of surface air temperature, pressure and precipitation of the Eurasian region to anomalies of ocean surface temperature associated with the Indian Ocean dipole// Monitoring systems of environment.  Sevastopol: INTS..  2018.  Issue. 11 (31). P. 83–89.
  7. Murtugudde R.G., McCreary J.P., Busalacchi A.J. Oceanic processes associated with anomalous events in the Indian Ocean with relevance to 1997–1998 // J. Geophys. Res., 105(C2). P. 3295–3306.
  8. Coupled ocean–atmosphere variability in the tropical Indian Ocean / T. Yamagata, S.K. Behera, J.-J. Luo [et al.] // Earth Climate: The Ocean–Atmosphere Interaction, Geophys. Monogr. Vol. 147, Amer.   Geophys.   Union. P. 189– 212.
  9. Three Types of Indian Ocean Dipoles.  / F. Guo, Q. Liu, S. Sun  [et al.]   //  J. Climate, 28. P. 3073–3092
  10. Allan R.J., Coauthors. Is there an Indian Ocean dipole, and is it independent of the El Niño–Southern Oscillation? CLIVAR Exchanges, No. 6, International CLIVAR Project Office, Southampton, United Kingdom. P. 18–22
  11. Saji N.H., Xie S.-P., Yamagata T. Tropical Indian Ocean variability in the IPCC twentieth-century climate simulations // J. Climate, 19. P. 4397–4417.
  12. Teleconnection pathways of ENSO and the IOD and the mechanisms for impacts on Australian rainfall /   W. Cai,   P.  van Rensch, T. Cowan [et al.]  //  J. Climate, 24. P. 3910–3923.
  13. Subsurface Interannual variability associated with the Indian Ocean Dipole / S.A. Rao, S.K. Behera, Y. Masumoto  [et al.]   //  Clivar Exchan.  2002.  № 7.  Р. 11 – 13.
  14. An asymmetry in the IOD and ENSO teleconnection pathway and its impact on Australian climate / W. Cai, P. van Rensch, T. Cowan  [et al.]  //  J. Climate, 25. P. 6318–6329.
  15. Influences of Indian Ocean interannual variability on different stages of El Niño: A FOAM1.5 model approach / X. Hong , H. Hu, X. Yang [et al.] //   Sci.   China:  Earth Sci.,  57. P. 2616–2627.
  16. Vinayachandran P.N., Lizuka S., Yamagata T. Indian Ocean dipole mode events in an ocean general circulation model // Deep Sea Res., Part II, 49 (7 – 8). P. 1573–1596.
  17. Polonsky A. B., Torbinsky A.V., Myers G. Interannual variability of the heat reserve of the upper layer of the Equatorial zone of the Indian ocean and the Indian Ocean dipole / / Marine hydrophysical journal. 2007. No. 3. P. 15 – 27
  18. Polonsky A. B., Torbinsky A.V. The role of zonal currents and planetary waves in the propagation of thermal anomalies in the Equatorial-tropical zone of the Indian ocean / / Marine hydrophysical journal. 2012. No. 6. P. 35-44.
  19. Lubkov A. S., Voskresenskaya E. N., Marchukova O. V. Modern El Nino classification and comparison of corresponding climate responses in the Atlantic-Eurasian region // Monitoring systems of environment.  Sevastopol: INTS.  2017.  Issue. 7(27).  P. 94 – 100.

Loading