# Presentation: 376977

## 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***

**Decadal variability in the Indo-Pacific ocean inferred from satellite data and ECCO assimilation**

- Reference for observational part: Lee and McPhaden (2008), GRL, Jan. 15 issue

**Notes:**
collaborator

## 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](http://www.ecco-group.org/)__) & ECCO-2 (__[http://ecco2-org](http://ecco2-org/)__, hi-res) ODA products._

## Decadal tendencies change sign around yr 2000. SSH in many regions forced by near-local wind (tilted arrows reflect ocean adjustment by Rossby waves) 

**Decadal tendencies change sign around yr 2000. SSH in many regions forced by near-local wind (tilted arrows reflect ocean adjustment by Rossby waves) **

**SSH trend for 1993-2000 (T/P altimeter)**

**SSH trend for 2000-2006 (T/P,Jason-1 altimeters)**

**Wind stress curl trend for 1993-2000 (ERS scat)**

**Wind stress curl trend for 2000-2006 (QuikSCAT)**

- cm/yr

- dyn/cm2/yr

## SSH time series (black curves) in key regions further illustrate the tendency change around 2000

**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?

**Notes:**
Have implications to horizontal & meridional circulations in the Pac & Indian Oceans. MOC focus.

## Schematics for zonally averaged view and horizontal view of time-mean Pacific & Indian-Ocean shallow MOCs

**Notes:**
Wind data – upper branch. E-W SSH difference between coasts: thermocline flow

## Implications of observed decadal wind & SSH to MOCs

**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**

**Notes:**
SE IO lags NW Pac 6-12 months

## Volume (left) & temperature (right) fluxes of the Indonesian throughflow estimated by ECCO products

**Volume (left) & temperature (right) fluxes of the Indonesian throughflow estimated by ECCO products**

**Notes:**
Acknowledge Michael Shodlok for computing fluxes from ECCO-2 product

## Observed decadal change of Indian-Ocean trade wind & MOC strength estimated by ECCO assimilation

**Trade wind**

**Estimated MOC**

## Comparison of SSH trend for 1993-2000 (indicative of DecVar): large-scale similarity

**Comparison of SSH trend for 1993-2000 (indicative of DecVar): large-scale similarity**

- Altimeter data

- ECCO-JPL estimate

- Used to estimate gyre circulation changes

**Notes:**
Although low-res model couldn’t resolve eddies, it represents large-scale trend relatively well.

## Slide 10

**Notes:**
NE corner consistent with Douglas et al. 2006 using XBT, though referred to as interannual; S Pac consistent with Roemmich et al 2007. about
spinup

## Summary

**Near-coherent decadal tendency changes SSH & wind in the Indo-Pacific region at the end of the 20****th**** 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.**

## Decadal signals from Reynolds SST

- PDO index

- Nino3.4 index

**Decadal signals from Reynolds SST**

## SSH time series (black curves) in key regions further illustrate the tendency change around 2000

**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?

**Notes:**
Have implications to horizontal & meridional circulations in the Pac & Indian Oceans. MOC focus.