Equatorial currents and transports in the upper central Indian Ocean: Annual cycle and interannual variability

Reppin, Jörg; Schott, Friedrich; Fischer, Jürgen; Quadfasel, Detlef

doi:10.1029/1999jc900093

Cited by 173 publications

(185 citation statements)

References 32 publications

(15 reference statements)

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“…Reppin et al [1999] also reported that biweekly meridional current variation was clearly observed in results of similar mooring observations on the equator south of Sri Lanka (80.5°E) from 1993 through 1994. Recently, Masumoto et al [2005] observed the current variability in the upper 400 m depth in the eastern equatorial Indian Ocean (0°N, 90°E) from November 2000 to October 2001 with an upward looking acoustic Doppler current profiler (ADCP).…”

Section: Introductionsupporting

confidence: 55%

Intraseasonal meridional current variability in the eastern equatorial Indian Ocean

et al. 2008

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[1] Intraseasonal variability in meridional current in the eastern equatorial Indian Ocean is investigated by use of results from a high-resolution ocean general circulation model. Both the simulated and observed meridional current variability demonstrate energy peaks in two distinct time-scales; one in the biweekly (6-8 d) period above the thermocline and the other in lower frequency band (20-70 d) within the subsurface layer. In addition, the intraseasonal current variability can be seen even in the deep ocean at 2000 m and 4000 m depths. Composite analysis of the biweekly current field demonstrates that the horizontal structure is consistent with the one for the Mixed Rossby-gravity wave, with the phase speed and wavelength close to theoretical values of the Mixed Rossby-gravity wave at 15-d period. This meridional current variability shows large coherence with the local meridional wind stress, suggesting the upper-ocean responses to the local wind-forcing. A part of the energy of the biweekly variability penetrates into the deeper layer along the raypath of the 15-d Mixed Rossby-gravity wave, causing the intraseasonal variability observed in the current meter data at 4000 m depth. On the other hand, the lower frequency intraseasonal variability in the subsurface layer is also captured in the model simulation forced by climatological winds. Large barotropic energy conversion rate appears during boreal autumn and early winter in a region southeast of Sri Lanka, suggesting importance of instability due to the seasonally changing current systems to generate mesoscale eddy-like disturbances that result in the subsurface meridional current variability.

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Section: Introductionsupporting

confidence: 55%

Intraseasonal meridional current variability in the eastern equatorial Indian Ocean

et al. 2008

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“…In the equatorial Indian Ocean, strong westerly winds dominate in boreal spring and fall during the monsoon transition seasons, and drive the eastward surface currents known as Wyrtki Jets (Wyrtki 1973;Reppin et al 1999). These jets trap the momentum from which the zonal winds input into the oceans in the upper 100 m and significantly influence the climate via horizontal heat, salt and mass transport in the tropical Indian Ocean (Murtugudde et al 2000).…”

Section: Introductionmentioning

confidence: 99%

“…In the equatorial Pacific and Atlantic Oceans, the prevailing easterly trade winds exist all year that drive a quasi-permanent eastward EUC, however, the EUC is transient in the Indian Ocean (McPhaden 1986). On seasonal time scales, the EUC is most prominent during boreal winter and spring, particularly from February to April, and with a secondary and much weaker peak in boreal late summer to early fall (Knox 1976;McPhaden 1982;Reppin et al 1999;Izumo 2005;Iskandar et al 2009). On interannual time scales, the summer-fall EUC in the central and eastern equatorial Indian Ocean becomes stronger during the pIOD events than during normal period (Reppin et al 1999;Swapna and Krishnan 2008;Iskandar et al 2009), which feeds and intensifies the upwelling off the Sumatra-Java coast, producing a positive feedback to the decrease of SST in this region (Thompson et al 2006;Nyadjro and McPhaden 2014;Zhang et al 2014;Chen et al 2016).…”

Section: Introductionmentioning

confidence: 99%

Impacts of the IOD-associated temperature and salinity anomalies on the intermittent equatorial undercurrent anomalies

Liang

Tang

et al. 2017

Clim Dyn

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“…The Japan Marine Science and Technology Center (JAMSTEC) deployed a moored acoustic Doppler current profiler (ADCP) in November 2000 at 400-m depth at 0°, 90°E (Masumoto et al 2005), and a Triangle Trans-Ocean Buoy Network (TRITON) buoy in October 2001 at 1.6°S, 90°E (Kuroda 2002). Ongoing observations from these instruments already cover a longer period than previous in situ time series measurements in the EqIO, including those from Gan Island, Republic of Maldives (Knox 1976;McPhaden 1982), the western EqIO (Luyten and Roemmich 1982), and south of Sri Lanka (Schott et al 1994;Reppin et al 1999).…”

Section: Introductionmentioning

confidence: 99%

Intraseasonal Variability of Equatorial Indian Ocean Zonal Currents

et al. 2007

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New satellite and in situ observations show large intraseasonal (10-60 day) variability of surface winds and upper-ocean current in the equatorial Indian Ocean, particularly in the east. An ocean model forced by the Quick Scatterometer (QuikSCAT) wind stress is used to study the dynamics of the intraseasonal zonal current. The model has realistic upper-ocean currents and thermocline depth variabilities on intraseasonal to interannual scales. The quality of the simulation is directly attributed to the accuracy of the wind forcing. At the equator, moderate westerly winds are punctuated by strong 10-40-day westerly wind bursts. The wind bursts force swift, intraseasonal (20-50 day) eastward equatorial jets in spring, summer, and fall. The zonal momentum balance is between local acceleration, stress, and pressure, while nonlinearity deepens and strengthens the eastward current. The westward pressure force associated with the thermocline deepening toward the east rapidly arrests eastward jets and, subsequently, generates (weak) westward flow. Thus, in accord with direct observations in the east, the spring jet is a single intraseasonal event, there are intraseasonal jets in summer, and the fall jet is long lived but strongly modulated on an intraseasonal scale. The zonal pressure force is almost always westward in the upper 120 m, and changes sign twice a year in the 120-200-m layer. Transient eastward equatorial undercurrents in early spring and late summer are associated with semiannual Rossby waves generated at the eastern boundary following thermocline deepening by the spring and fall jets. An easterly wind stress is not necessary to generate the undercurrents. Experiments with a single westerly wind burst forcing show that apart from the intraseasonal response, the zonal pressure force and current in the east have an intrinsic 90-day time scale that arises purely from equatorial adjustment.

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Equatorial currents and transports in the upper central Indian Ocean: Annual cycle and interannual variability

Abstract: Abstract.The

Cited by 173 publications

References 32 publications

Intraseasonal meridional current variability in the eastern equatorial Indian Ocean

Intraseasonal meridional current variability in the eastern equatorial Indian Ocean

Impacts of the IOD-associated temperature and salinity anomalies on the intermittent equatorial undercurrent anomalies

Intraseasonal Variability of Equatorial Indian Ocean Zonal Currents

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