Eddy variability in the subtropical South Indian Ocean:

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Eddy variability in the subtropical South Indian
Ocean relation to low-frequency changes of
large-scale flow local vs remote forcings Tony
Lee JPL
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(No Transcript)
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Longitude-time plot of observed SSH in
subtropical South Indian Ocean showing decadal
signal spreading out from the east.
Multi-altimeter AVISO data
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SSH trend for 1993-2000 1993-2004
(multi-altimeter AVISO data) different decadal
tendency before after 2000 in many regions.
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Trends of observed SSH wind stress curl for
1993-2000
SSH rise due to trop. Pac. wind

• Working hypothesis for SSH in subtropical S.
  Indian Ocean
• tropical Pacific wind cause rising SSH
• cause stronger Leeuwin Current
• shed off more/stronger eddies ( SSH)

Local wind did not cause SSH rise
Stronger trade wind
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Comparison of SSH trend for 1993-2000 in the
Indian Ocean (cm/yr) eddies vs. large-scale
Rossby waves resolution matters here!
Influenced by eddies
Dominated by large-scale Rossby Waves
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Co-varying SSH Eddy Kinetic Energy in
subtropical southeastern Indian Ocean (90-120E,
16-35S, normalized by std. dev.) supports the
aforementioned working hypothesis.
Cube21 simulation
Multi-altimeter AVISO data
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Summary

• Unique eddy characteristics in the subtropical
  South Indian Ocean
• Different behaviors from those in subtropical
  Pacific and Atlantic Oceans observations ECCO2
  model are used to understand their physics.
• Co-variability of eddy variability large-scale
  flow
• Occurring both on interannual decadal time
  scales (well captured by ECCO2 model).
• Mechanism
• Tropical Pacific wind cause interannual-to-decadal
  variation of sea level in the western tropical
  Pacific, which spill over to the eastern Indian
  Ocean to affect the strength of Leeuwin Current
  and subsequent westward radiation of
  Leeuwin-Current eddies.
• Ongoing work
• Instability analysis using ECCO2 solutions.
  Impact of eddies on heat salt transports.