Indonesian Throughflows and Equatorial Currents

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Indonesian Throughflows and Equatorial Currents

• Eric Leibensperger
• EPS 131

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Indonesian Throughflow

• System of surface currents flowing from the
  Pacific Ocean to the Indian Ocean through the
  Indonesian Seas.
• Important because it is the only low latitude
  transport between oceans
• Even more important because one of the oceans is
  the warm Western Pacific

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Importance of ITF

• Connection of warm Pacific waters to the cooler
  waters of Indian Ocean.
• Large part of E-W transport of heat in climate
  system
• Transports 12 Sv of warm, low salinity water

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Why study ITF?

• Transport can vary up to 100 seasonally and
  annually.
• Transfer of heat affects the rain (or lack of
  rain) and fire seasons of Northwest Australia and
  Southeast Asia, thus is a large environmental and
  economic factor.

• Without ITF, region would be colder and drier.
• Area of large air-sea interaction (because it is
  so warm).

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Why so warm?

• The equatorial region in the western Pacific is
  very warm. Below The warmer waters of the
  western Pacific reach deeper than the eastern
  Pacific. With diverging Ekman transport at the
  equator, upwelling brings up warm water in the
  west and cooler water in the east.

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Why so warm? Contd
Result of Indonesian Throughflow!!

• Warm water increases evaporation, which increases
  heat released from condensation in the atmosphere
  and rainfall. The fluctuations of the ITF affect
  the ocean, land and atmosphere.

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A Very Grainy Movie, but
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Equatorial Currents
North Equatorial Current 20 cm/sec, 200m deep
North Equatorial Countercurrent Between 3-10N,
50 cm/sec, centered around tropical convergence
zone (where N-S trade winds converge), 20Sv
South Equatorial Current Max of 100 cm/sec, 200m
deep
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North Equatorial Countercurrent

• Responsible for eastern heat flow.
• In Pacific, on the eastern edge (diverges) into
  two currents, the northern divergence supplies
  the California countercurrent.
• Intensifies during El Nino events.

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Equatorial Undercurrents

• First noticed in 1950s by a United States Fish
  and Wildlife team fishing for tuna south of
  Hawaii.

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More on Undercurrents

• Surface flows west, but starting between 20-40m
  the undercurrent is towards the east.
• Extends to 400m and can transport up to 30 Sv.
• Symmetrical about equator, dying off by 2ºN and
  S.
• Max velocities of 1.5 m/sec.
• Explanation still not fully understood, but
  thought to be a result of the conservation of
  potential vorticity.

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Tying it all together
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References

• CSIRO Marine Research, Indonesian Throughflow
  Facts, http//www.marine.csiro.au/LeafletsFolder/p
  dfsheets/64indothroughflow.pdf
• Fundamentals of Physical Geography,
  http//www.physicalgeography.net
• Introduction to the Indian Ocean,
  http//indianocean.free.fr/intro.html
• Philander, S.G.H. (1980), The Equatorial
  Undercurrent Revisited. Ann. Rev. Earth Planet
  Sci., 8, 191-204.
• Stewart, R.(2005). Introduction to Physical
  Oceanography, http//oceanworld.tamu.edu/resources
  /ocng_textboo k/contents.html