Tropical Pacific decadal oscillation Tropical Pacific decadal oscillation driven by the interaction driven by the interaction

between ENSO and mean state between ENSO and mean state

Tropical Pacific decadal oscillation Tropical Pacific decadal oscillation driven by the interaction driven by the interaction

between ENSO and mean state between ENSO and mean state

Jung ChoiJung Choi , Soon-Il An , Soon-Il An

Climate Theory Laboratory,Department of Atmospheric Sciences,

Yonsei University, Seoul, Korea

Fedorov & Philander(2000)

Introduction

ENSO-like interdecadal variability in Tropical Pacific (Tropical Pacific Decadal Variability) ~ Decadal ENSO amplitude modulations

The physical mechanism is still unknown.

ENSOENSO

TPDVTPDV

SeasonalCycle

SeasonalCycle

Externalinfluence

Externalinfluence

Internal mode

TPDVTPDV

ENSOENSO

Introduction

Data

Ocean model OPA 8 GCM2°X 2°

(tropics lat :0.5°)

31 vertical levels

Sea ice model L-L-NHibler-type dynamic-

thermodynamic

Atmos. model ARPEGE : T63 31 vertical levels

Initial ocean stateLevitus (Antonov et al. 1998)

- temperature, salinity, sea ice

Integration period

260-yr

(last 200-yr for analysis

– monthly mean data)

(Dewitte et al. (2006, 2007), Cibot et al. (2005))

ENSO modulation

Biennial ENSO

Averaged power (2-7yr waves) N3Var index (Torrence & Webster)

Wavelet of Nino3 SSTA

N3Var index ENSO modulation (16-year)

Correlation between ENSO and mean state

Changes of mean state Lowpass-filtered (>7yr) SSTA , D17

(LSST)

(LD17)

Correlations

High-Var regime

Low-Var regime

N3Var

LD17

LSST

Correlation :: (N3Var ~ LD17)

0.54

Nonlinear rectification(ENSO mean state)

Mature phase

Transition phase

Mature phase PC

Tra

nsit

ion

PC

Asymmetry of ENSO EOF of Highpass-filtered (<7yr) D17

Positive feedback?

Residual heat content rectifies the mean state.

Mean state supports the High-Var ENSO conditions.

Decadal variability ENSO

Role of mean state(mean state ENSO)

Eigen analysis

Background field(mean state)

Generate Matrix

Eigenanalysis

SST, Wind,Thermocline depth,

Upwelling ... etc.

Based on CZ intermediate ENSO model

1st Eigenvector(most unstable mode)

Normalized PC1 of LD17

Composite the mean state on each 1,2,3,4 (SST, thermocline depth)

Experimental design

0.5

-0.5

0.5

-0.5

High-Var regime

Low-Var regime

1

2

3

4

1

2

3

Frequency [1/years]

0.22 0.24 0.26 0.28 0.30 0.32 0.34 0.36

Gro

wth

rat

e [1

/yea

rs]

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

SSTZ17SST+Z17CNTL

1SST

TH

1

1

ENSO Growth rate & Frequency

SST+TH

Deepening H in E. Pacific

ENSO unstable regime

Increasing asymmetry &

amplitude of ENSO

Warming SST

in E. Pacific

Reduction of Growth rate

SustainENSO

ENSO stable regime

Decreasing asymmetry

& amplitude of ENSO

Shoaling H in E. Pacific

Cooling SSTin E. Pacific

Increasing of Growth rate

Damp down ENSO

< Schematic diagram for TPDO >