Physical Oceanography, Vol. 17, No. 3, 2007
ANALYSIS OF OBSERVATIONS AND METHODS FOR CALCULATING
HYDROPHYSICAL FIELDS IN THE OCEAN
INTERANNUAL VARIABILITY OF THE HEAT CONTENT OF THE UPPER LAYER
IN THE EQUATORIAL INDIAN OCEAN AND THE INDIAN-OCEAN DIPOLE
A. B. Polonskii,
A. V. Torbinskii
The aim of the present work is to study the characteristics of interannual variability of the heat
content of the upper layer in the Equatorial Indian Ocean according the XBT-data accumulated in
1983–2003 for the evaluation the role of various physical factors specifying the space and time
structure of the Indian-Ocean dipole in the subsurface layer. The existence of the significant in-
fluence of intense events of El Niño on the Indian-Ocean dipole is confirmed. These events gen-
erate the maximum disturbances of the thermal structure in the upper layer of the east part of the
Indian Ocean propagating then in the westward direction with velocities varying from
The Indian-Ocean dipole (IOD) is one of the main modes characterizing the interannual variability of large-
scale interaction between the ocean and atmosphere in the equatorial zone of the World Ocean. This dipole
manifests itself in the form of the opposite phases of interannual oscillations of the parameters of interaction be-
tween the ocean and atmosphere in the west and east parts of the equatorial zone of the Indian Ocean. As an ex-
ample, in Fig.
1, we display the coefficients D
of wavelet expansion of the January turbulent heat fluxes
computed according to the data of NCEP reanalysis in the central and east parts of equatorial zone of the Indian
Ocean for 1950–2001. These coefficients clearly reveal the antiphase character of variations of the turbulent
heat fluxes in the analyzed regions on time scales from several to ten years. The Indian-Ocean variations of this
type form a considerable fraction of the interannual fluctuations of the climatic characteristics not only in the
regions close to the Indian Ocean but also in the Atlantic-European region [1–5]. For this reason, significant at-
tention of the researchers is given in recent years to the investigation of the IOD. In numerous works (see, e.g.,
[1, 2]), the IOD is regarded as an independent mode of the equatorial variability in the Indian Ocean. The other
authors [3, 4, 6] believe that the IOD is correlated with the El Niño–Southern Oscillation (ENSO) mainly via the
Indian-Ocean and Pacific equatorial Walker cells.
In the subsurface layer, the IOD is revealed in the temperature field . However, the characteristics of in-
terannual variability of this field are studied much poorer than the variability of the atmospheric parameters and
sea-surface temperature. This can be explained by the fact that the amount of available oceanographic data is
much smaller than the amount of available meteorological data.
Marine Hydrophysical Institute, Ukrainian Academy of Sciences, Sevastopol.
Department of Oceanography of CSIRO, Hobart, Australia.
Translated from Morskoi Gidrofizicheskii Zhurnal, No.
15–27, May–June, 2007. Original article submitted January 13, 2006;
revision submitted January 25, 2006.
0928-5105/07/1703–0129 © 2007 Springer Science+Business Media, Inc. 129