Dynamics of zonal current variations associated with the Indian Ocean dipole

Nagura, Motoki; McPhaden, Michael J.

doi:10.1029/2010jc006423

Cited by 92 publications

(82 citation statements)

References 46 publications

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“…The first EOF mode (EOF1) of zonal currents and wind stress (Figure 4a) shows easterly wind stress peaking at about 85 E, while the zonal current peaks further west at about 75 E. Peak correlation between zonal currents and winds is 0.8, with zonal currents leading zonal winds by about a month (Figure 5a). This phase relationship is unexpected if we think only in terms of direct wind-forcing of the ocean and it is most likely due to influence on zonal current variability of reflected Rossby waves generated at the eastern boundary [Nagura and McPhaden, 2010b]. EOF1 accounts for 80% (67%) of the zonal current (windstress) variance.…”

Section: Interannual Variability Of the Wyrtki Jetsmentioning

confidence: 94%

“…Thompson et al [2006], using the modular ocean model (MOM4), carried out extensive analysis on the anomalous zonal and meridional circulation associated with IOD. The anomalous winds associated with IOD are maximum over the central equatorial Indian Ocean and act as a direct local forcing, though westward propagating Rossby waves generated at the eastern boundary are also important [Nagura and McPhaden, 2010b].…”

Section: Introductionmentioning

confidence: 99%

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Impact of Indian Ocean Dipole and El Niño/Southern Oscillation wind‐forcing on the Wyrtki jets

2012

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[1] Interannual variability of the Wyrtki jets is studied in the context of Indian Ocean Dipole (IOD) and El Niño and Southern Oscillation (ENSO) wind-forcing using a three dimensional numerical ocean model and observations. The boreal fall (October-November) Wyrtki jet is more significantly affected than the boreal spring (April-May) Wyrtki jet since both the IOD and ENSO tend to peak toward the end of the calendar year. Various statistical methods are used in an attempt to separate the impacts of the IOD and ENSO on these jets, with emphasis on the fall jet. The first two modes of an Empirical Orthogonal Function (EOF) decomposition account for about 90% and 85% of variability in zonal currents and wind stress respectively along the equator in the Indian Ocean, but EOF analysis does not cleanly separate out IOD and ENSO forcing and response. Partial correlation analysis reveals that IOD wind-forcing and zonal equatorial current response are stronger on average than for ENSO and extend further west across the basin. Composite analysis of IOD only, ENSO only, and combined IOD and ENSO years provides a complementary definition of the relative contributions of these two phenomena on Wyrtki jet variability and in general is consistent with the results of the partial correlation analysis.

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Section: Interannual Variability Of the Wyrtki Jetsmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

Impact of Indian Ocean Dipole and El Niño/Southern Oscillation wind‐forcing on the Wyrtki jets

2012

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“…The dipole pattern may affect the entire tropical Indian Ocean and is strongly expressed on a zonal dome or ridge in the thermocline which occurs on 4º-12º S between 45º-90º E. In-situ observations have been used to link the processes involved (Jury and Harrison, 1999;Roemmich and Owens, 2000;Ehrlich et al, 2002); and data from an array of moored buoys covering the tropical Indian Ocean is now available (McPhaden et al, 2009). Interannual oscillations of SST in the southern tropics are governed by wind-forced Rossby waves that undulate westward on the well known thermocline ridge (McCreary et al, 1993;Sengupta et al, 2001;Xie et al, 2001;Huang and Kinter, 2002;Jury and Huang, 2004;Nagura and McPhaden, 2010). Coupled models have been evaluated to determine their ability to represent this feature and its impacts (Behera et al, 2006).…”

Section: Introductionmentioning

confidence: 99%

Variability in the Tropical Southwest Indian Ocean and Influence on Southern African Climate

Jury¹

2013

ijms

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This study considers satellite era reanalysis products to characterize inter-annual variability in the SW Indian Ocean and influence on the climate of southern Africa. Decorrelation of temperature from a buoy area (8°S, 55°E) is found to vary by season; widespread in the first half of the year and almost zero in the second. This leads to an analysis of the annual cycle and inter-annual variability via wavelet filtered principal components. Contrasts between SODA and GODAS reanalysis products reveal the former exhibits higher amplitude annual to inter-annual variability. Good agreement is found for sub-surface temperature in the SW Indian Ocean thermocline ridge, with rhythmic fluctuations of 2.5-5 yr period. When an ocean Rossby wave crest arrives in the southwestern part of the basin, increased SST and local convective rainfall alters the large-scale circulation. The NW monsoon becomes active and moisture that would normally be exported to southern Africa is retained in the SW Indian Ocean. Daily data from a mooring at 8°S, 55°E reveals intra-seasonal pulses at 15-50 days in Nov.-Mar. season. Intercomparisons with satellite and reanalysis data reveal a cool bias in NCEP during the SE monsoon. Hovmoller analysis highlights how surges in NW monsoon winds relate to heat fluxes and rossby wave patterns. A case study is made to contrast Dec.-Mar. 2011 vs 2012, the former having negative sea surface height anomalies, the latter being positive. Regional wind responses to SW Indian Ocean heat anomalies contribute to a 15% change in seasonal rainfall and maize production in South Africa.

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“…In April strong westerly wind anomalies occurred along the equator that forced eastward zonal current anomalies, which are associated with the down welling equatorial Kelvin waves. Note that the eastward zonal current anomalies reveal westward phase propagation during April -May indicating the important role of Rossby waves in generating this westward phase propagation (Nagura and McPhaden 2010b). Previous studies have shown that the eastern-boundary reflected upwelling Rossby waves from the incoming upwelling Kelvin waves play an important role in zonal current variations along the equatorial Indian Ocean McPhaden 2010b: Iskandar et al 2013).…”

Section: Role Of Equatorial Wavesmentioning

confidence: 79%

Equatorial Oceanic Waves and the Evolution of 2007 Positive Indian Ocean Dipole

Iskandar¹,

Mardiansyah²,

Setiabudidaya³

et al. 2014

Terr. Atmos. Ocean. Sci.

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The role of equatorial oceanic waves on the evolution of the 2007 positive Indian Ocean Dipole (pIOD) event was evaluated using available observations and output from a quasi-analytical linear wave model. It was found that the 2007 pIOD event was a weak and short-lived event: developed in the mid-summer (July), matured in the early-fall (September), and terminated in the mid-fall (October). The evolution of the 2007 pIOD event was linked to the equatorial wave dynamics. The event development was associated with the generation of upwelling equatorial Kelvin waves (westward current anomalies) generated by easterly wind anomalies. The event termination was associated with the occurrence of eastward zonal current anomalies resulting from a complex interplay between the wind-forced down welling Kelvin waves and the eastern-boundary-reflected Rossby waves. Results from a quasi-analytical linear wave model show that during the event development and maturation, the wind-forced Kelvin waves played a dominant role in generating zonal current anomalies along the equatorial Indian Ocean, while the easternboundary-reflected Rossby waves tended to weaken the wind-forced Kelvin wave signals. During the event termination our model shows that the initiation of anomalous eastward current resulted from the reflected Rossby waves at the eastern boundary. The wind-forced Kelvin waves associated with the seasonal reversal of the monsoon further strengthened the eastward zonal currents generated by the boundary-generated Rossby waves in late-October/early-November. This highlights the importance of the eastern-boundary-reflected Rossby waves on the IOD event termination.

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Dynamics of zonal current variations associated with the Indian Ocean dipole

Cited by 92 publications

References 46 publications

Impact of Indian Ocean Dipole and El Niño/Southern Oscillation wind‐forcing on the Wyrtki jets

Impact of Indian Ocean Dipole and El Niño/Southern Oscillation wind‐forcing on the Wyrtki jets

Variability in the Tropical Southwest Indian Ocean and Influence on Southern African Climate

Equatorial Oceanic Waves and the Evolution of 2007 Positive Indian Ocean Dipole

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