Physical Oceanography, Vol.
THERMOHYDRODYNAMICS OF THE OCEAN
VELOCITY OF PROPAGATION OF TEMPERATURE ANOMALIES
IN THE TROPICAL ZONE OF THE INDIAN OCEAN
A. B. Polonskii and A. V. Torbinskii
We describe the space-and-time structure of large-scale thermal anomalies in the upper layer in
the tropical zone of the Indian Ocean and study the mechanism of their formation. It is shown
that the critical layer in which the phase velocities of propagation of disturbances coincide with
the mean velocity of the zonal current can be formed in the central part of equatorial zone of the
Indian Ocean (between 9° and 12°S). In this layer, the formation of growing disturbances is pos-
sible due to the barotropic-baroclinic instability of the system of zonal currents.
The processes of circulation and advective heat transfer in the Indian Ocean are characterized by the pre-
sence of well-pronounced specific features as compared with the Pacific and Atlantic Oceans. The Asian conti-
nent blocks the ocean from the north and, as a result, the heat accumulated in the tropical zone cannot be carried
out to high latitudes of the Northern hemisphere by the advective flows, as in the Atlantic and Pacific Oceans.
The Indian Ocean also receives additional heat from the Pacific Ocean through the Indonesian Straits . Thus,
the Indian Ocean plays the role of one of the main sources supplying heat to the southern part of the Atlantic
Ocean. Hence, the processes of redistribution of heat inside the equatorial-tropical zone of the Indian Ocean are
not only of the regional interest . The influence of the processes running in this zone of the Indian Ocean on
the heat exchange with the atmosphere on the interannual scale and the variations of the regional climate is real-
ized mainly via the Indian-Ocean Dipole supported, to a large extent, by the advective heat transfer in the ocean.
Indeed, the Indian-Ocean Dipole is the main interannual mode in the ocean–atmosphere system of the equatorial
tropical zone of the Indian Ocean. The space-and-time scales of this mode are usually associated with the char-
acteristics of Rossby waves generated in the east part of the Indian Ocean between
to the west with a velocity of
increasing in the direction of the equator . The indicated phase vel-
ocity and the corresponding zonal dimensions of the Indian Ocean are responsible for the formation of the inter-
annual variability of the characteristics of the ocean–atmosphere system in this region of the World Ocean .
If the phase velocity of Rossby waves changes, then one can expect the corresponding changes in the typi-
cal period of the Indian-Ocean Dipole. As one of the main factors specifying the velocity of Rossby waves at a
given latitude, one can mention the presence of a mean zonal current. As shown in , the phase velocity of
propagation of disturbances in the field of accumulated heat decreases in the east–west direction in the vicinity
7–8°S. In , this is explained by the influence of zonal currents on the characteristics of these waves. In the
present work, we check this assumption by using more complete data of observations in the equatorial tropical
Marine Hydrophysical Institute, Ukrainian Academy of Sciences, Sevastopol, Ukraine.
Translated from Morskoi Gidrofizicheskii Zhurnal, No.
3–11, March–April, 2009. Original article submitted October 9, 2007,
revision submitted November 26, 2007.
0928-5105/09/1902–0063 © 2009 Springer Science+Business Media, Inc. 63