section, the velocities of the eastern jets are reduced to 10–20 cm/s. Note that the
eastward flow extends over this section to a maximum observation depth of 700 m
with velocities up to 30 cm/s.
At 68° E, the Tareev Current is slightly weaker and deeper. The core of the
current disintegrates into separate jets, the depth of which ranges from 50 to 100 m,
and the speed in the jets becomes lower than 50 cm/s. In general, there is a deviation of the core and individual stream jets to the north. In the southern part of the
section, the Tareev Current begins to weaken south of 2° S, where the velocity falls
to 20 cm/s. Nevertheless, the current can be seen up to the end of the section. At the
northern stations of the section, the speed of the undercurrent is still quite high,
thus, we can assume that it extends noticeably north of 3° N. The width of the
current in the meridional direction over this section is more than 700 km. Below,
the jets of the stream of the eastern direction are weaker and interspersed by the
counter flows, the number of which considerably increases below 300 m (not
shown in the figure).
Thus, we can formulate the following conclusions:
(1) A strong surface eastward current with velocities exceeding 40 cm/s was
observed in the equatorial region of the Indian Ocean in the winter season of the
Northern Hemisphere in February 2017. During the entire observation period,
the northeastern winds with speeds of 5–12 m/s dominated.
(2) A thin surface westward current was observed over the meridional section
along 68° E from 3° N to 3° S at all stations at depths from 0 to 50 m. Below
them, the eastward equatorial undercurrent (Tareev Current) was recorded at
depths of 50–150 m with velocities ranging from 20 to 50 cm/s. At the
southern end of the section, the currents were much weaker.
(3) The Tareev Current is clearly observed over the 65° E meridional section from
2.5° S to 1° N. The undercurrent core is located in the equatorial region within
one degree in the meridional span. At the ends of the section the flow weakens
and it is masked by the vortex perturbations.
(4) The width of the Tareev equatorial current, according to our measurements, was
more than 700 km over the section along 68° E and about 350 km over the
65° E section.
Thus, we can conclude that in February 2017 subsurface equatorial undercurrent
exists during the time of the development of the western surface current generated
by the northeastern summer monsoon in the equatorial zone of the Indian Ocean.
The development of this flow spans from east to west and, ultimately, transforms to
the flow of the eastern direction, existing during the winter monsoon as a subsurface
undercurrent.
Acknowledgements The R/V “Akademik Boris Petrov” expedition was supported by the Federal
Agency for Scientific Organizations of Russia and with the assistance of the Agency staff. The
analysis was supported by the Russian Science Foundation, grant 14-50-00095. We thank all the
participants of this expedition, including the scientific team and crew of the ship, who facilitated
the scientific observations.
498
A. K. Ambrosimov et al.
eastward flow extends over this section to a maximum observation depth of 700 m
with velocities up to 30 cm/s.
At 68° E, the Tareev Current is slightly weaker and deeper. The core of the
current disintegrates into separate jets, the depth of which ranges from 50 to 100 m,
and the speed in the jets becomes lower than 50 cm/s. In general, there is a deviation of the core and individual stream jets to the north. In the southern part of the
section, the Tareev Current begins to weaken south of 2° S, where the velocity falls
to 20 cm/s. Nevertheless, the current can be seen up to the end of the section. At the
northern stations of the section, the speed of the undercurrent is still quite high,
thus, we can assume that it extends noticeably north of 3° N. The width of the
current in the meridional direction over this section is more than 700 km. Below,
the jets of the stream of the eastern direction are weaker and interspersed by the
counter flows, the number of which considerably increases below 300 m (not
shown in the figure).
Thus, we can formulate the following conclusions:
(1) A strong surface eastward current with velocities exceeding 40 cm/s was
observed in the equatorial region of the Indian Ocean in the winter season of the
Northern Hemisphere in February 2017. During the entire observation period,
the northeastern winds with speeds of 5–12 m/s dominated.
(2) A thin surface westward current was observed over the meridional section
along 68° E from 3° N to 3° S at all stations at depths from 0 to 50 m. Below
them, the eastward equatorial undercurrent (Tareev Current) was recorded at
depths of 50–150 m with velocities ranging from 20 to 50 cm/s. At the
southern end of the section, the currents were much weaker.
(3) The Tareev Current is clearly observed over the 65° E meridional section from
2.5° S to 1° N. The undercurrent core is located in the equatorial region within
one degree in the meridional span. At the ends of the section the flow weakens
and it is masked by the vortex perturbations.
(4) The width of the Tareev equatorial current, according to our measurements, was
more than 700 km over the section along 68° E and about 350 km over the
65° E section.
Thus, we can conclude that in February 2017 subsurface equatorial undercurrent
exists during the time of the development of the western surface current generated
by the northeastern summer monsoon in the equatorial zone of the Indian Ocean.
The development of this flow spans from east to west and, ultimately, transforms to
the flow of the eastern direction, existing during the winter monsoon as a subsurface
undercurrent.
Acknowledgements The R/V “Akademik Boris Petrov” expedition was supported by the Federal
Agency for Scientific Organizations of Russia and with the assistance of the Agency staff. The
analysis was supported by the Russian Science Foundation, grant 14-50-00095. We thank all the
participants of this expedition, including the scientific team and crew of the ship, who facilitated
the scientific observations.
498
A. K. Ambrosimov et al.