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Int. J. of Marine Science 2012, Vol.2, No.7, 51
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Figure 3
The relationship between the kinetic energy of eddies and chlorophyll-
a
concentration exemplified for various years.
Note: A: 2003; B: 2001; C: 1998; D: 2007
number of regions. For instance, a cyclonic (highly
productive) eddy tracked in the Northern Arabian Sea
was about 100 km in diameter and has persisted for
about 4 weeks (from November to December) moving
towards the equator, accompanied by an anticyclonic
eddy of the same size (Tang et al., 2002). The authors
related the formation and decay of these eddies with
variations of the input of wind stress vorticity.
The bimodal seasonal cycle of chlorophyll-
a
(Figure 1)
is mediated by the reversal of the wind system over the
region (Banse, 1994; McCreary et al., 2009). Seasonal
development of the first and second peaks reflects the
timing of the Northeast (winter) and the Southwest
(summer) monsoons (Le´vy et al., 2007).
It was believed that in the western Arabian Sea,
mesoscale eddies are mostly associated with the
summer monsoon. Our data showed that both monsoon
periods could be accompanied by a well-developed
field of mesoscale eddies in the region. These data and
preceding publications-both imply a multilateral origin
of eddies. Some of them were associated with the
coastal circulation
—
the confluence of currents. For
instance, a steady structure consisting of two eddies
(cyclonic to the north and anticyclonic to the south of
the frontal jet) might be annually observed in the region
of Ras al Hadd cape of the Omani coast (Böhm et al.,
1999). The system is formed by the confluence of two
currents and persists through the time of the summer
monsoon. Truly oceanic eddies observed in the region,
were reportedly mediated by baroclinic instability of
currents and planetary (Rossby and Kelvin) waves
which generated densely packed eddy field
(Subrahmanyam and Robinson, 2000).
Gomes et al (2009)
have noticed that years with high
kinetic energy of eddies in the north Arabian Sea were
associated with high chlorophyll-
a
concentration. We
believe that the high value of kinetic energy does not
characterize and is not associated with the type of eddy
however; both types (cyclonic and anticyclonic) might
possess a high level of the available potential energy or
kinetic energy. In this regard, we provided insights into
the relation between the type of eddies (characterized
by the balance of positive to negative sea surface
heights), and kinetic energy.