Indonesian Throughflows and Equatorial Currents

Eric Leibensperger

EPS 131

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

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

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).

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.

Why so warm? Cont’d

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.

A Very Grainy Movie, but …

Equatorial CurrentsNorth Equatorial Current: 20 cm/sec, 200m deep

South Equatorial Current: Max of 100 cm/sec, 200m deep

North Equatorial Countercurrent: Between 3-10°N, 50 cm/sec, centered around tropical convergence zone (where N-S trade winds converge), 20Sv

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.

Equatorial Undercurrents

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

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.

Tying it all together

References:

• CSIRO Marine Research, Indonesian Throughflow Facts, http://www.marine.csiro.au/LeafletsFolder/pdfsheets/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