| Variability in the upper ocean currents in the eastern equatorial IndianOcean is investigated using 20 months velocity data, from November2000 to July 2002, obtained by an upward-looking ADCP moored at 90Eon the equator. The most energetic variability in the currents shallowerthan the thermocline appears in the intraseasonal time-scale, while theamplitude of the annual and semiannual signals, associated with themonsoonal winds and the Wyrtki jets, respectively, are rather small inthis location. Dominant periods of the intraseasonal variations are 30to 60 days for the zonal current and 5 to 15 days for the meridionalcomponent. However, the typical period of the variations is quitedifferent between the periods before and after November 2001; thevariation about 30 (60) days is dominant in the zonal current before(after) that time. In addition, the amplitude of the low-frequencyvariability in the meridional component of the upper-layer velocityafter November 2001 becomes large compared to that before thisparticular month. The above suggests that the interannual modulationof the intraseasonal variations is quite significant in this region. Thecorrelation analysis between the currents and the wind stress overthe equatorial Indian Ocean suggests that, before November 2001,the variability in the zonal current is excited by the zonal wind ataround 80E and, then, propagate to the east as the gravest equatorialKelvin wave. On the other hand, the dynamics of the current systemobserved during the period after November 2001 is explained by thelocally forced Yoshida jet. Comparison with the current meter on theTRITON mooring at 1.5S, 90E, indicates that the meridional scale ofthe intraseasonal variability observed after November 2001 is lessthan 1.5 degrees from the equator, suggesting rather narrow jetsconfined near the equator. |
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