Tong Lee

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Decadal variability in the Indo-Pacific ocean
inferred from satellite data and ECCO assimilation
Tong Lee NASA Jet Propulsion Laboratory,
California Institute of Technology Michael
McPhaden NOAA Pacific Marine and Environmental
Laboratory
Reference for observational part Lee and
McPhaden (2008), GRL, Jan. 15 issue
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Motivation
Linkages of DecVar of ocean circulation in the
Indo-Pacific region not well understood, e.g.,
the meridional overturning circulations (MOCs) of
the two oceans were studied separately (McPhaden
Zhang 2002/2004, Lee 2004).
Approach

• Analyze satellite observations of sea surface
  height (SSH) and ocean surface wind in the past
  15 years infer ocean circulation changes.
• SSH TOPEX/Poseidon (1992-2005) JASON-1
  (2001-present) altimeters
• Wind ERS (1991-2001) QuikSCAT
  (1999-present) scatterometers.
• Quantify ocean circulation changes using ECCO
  (http//www.ecco-group.org) ECCO-2
  (http//ecco2-org, hi-res) ODA products.

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Decadal tendencies change sign around yr 2000.
SSH in many regions forced by near-local wind
(tilted arrows reflect ocean adjustment by Rossby
waves)
cm/yr
SSH trend for 1993-2000 (T/P altimeter)
dyn/cm2/yr
Wind stress curl trend for 1993-2000 (ERS scat)
SSH trend for 2000-2006 (T/P,Jason-1 altimeters)
Wind stress curl trend for 2000-2006 (QuikSCAT)
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SSH time series (black curves) in key regions
further illustrate the tendency change around 2000

• Tropical Pacific leads other regions.
• The role of ENSO residuals on decadal time scales?

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Schematics for zonally averaged view and
horizontal view of time-mean Pacific
Indian-Ocean shallow MOCs
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Implications of observed decadal wind SSH to
MOCs
Decadal change of zonal wind meridional Ekman
flow (upper branch of MOC) reflect atmospheric
bridge (anomalous Walker Circulation).
Decadal change of E-W SSH difference
thermocline flow (lower branch of MOC) reflect
oceanic linkage (wave-transmission from NW
Pacific to SE Indian Oceans)
Anomalous pycnocline flow
Anomalous pycnocline flow
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Volume (left) temperature (right) fluxes of the
Indonesian throughflow estimated by ECCO products
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Observed decadal change of Indian-Ocean trade
wind MOC strength estimated by ECCO assimilation
Trade wind
Estimated MOC
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Comparison of SSH trend for 1993-2000 (indicative
of DecVar) large-scale similarity
Altimeter data
ECCO-JPL estimate
Used to estimate gyre circulation changes
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(No Transcript)
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Summary

• Near-coherent decadal tendency changes SSH wind
  in the Indo-Pacific region at the end of the 20th
  century broader than PDO.
• Equatorial Pacific SSH, forced by local trade
  wind, leads the changes.
• Anti-correlated changes of MOCs in the Pacific
  Indian Oceans, thus opposite roles in regulating
  tropical heat content atmospheric connection via
  Walker circulation oceanic linkage by ITF.
• Coherent variations of subtropical subpolar
  gyres atmospheric tele-connections.

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Decadal signals from Reynolds SST
PDO index
Nino3.4 index
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SSH time series (black curves) in key regions
further illustrate the tendency change around 2000

• Tropical Pacific leads other regions.
• The role of ENSO residuals on decadal time scales?