Soo-Hyun YooSoo-Hyun Yoo

Asian summer monsoons in the NCEP CFS;

Asian summer monsoons in the NCEP CFS; Possible Possible Role of the Southern Indian Ocean SST

Role of the Southern Indian Ocean SST

Soo-Hyun Yoo Soo-Hyun Yoo

Climate Prediction Center/NCEP Climate Prediction Center/NCEP

Acknowledgements: Song Yang (CPC/NCEP), John Fasullo (CGD/NCAR), Acknowledgements: Song Yang (CPC/NCEP), John Fasullo (CGD/NCAR),

and Chang-Hoi Ho (SNU)

and Chang-Hoi Ho (SNU)

Introduction and objectives

Possible role of IO SST in the Asian Monsoon and ENSO - Dominant features of Asian Monsoons and ENSO in summer

- Relative importance of Northern and Southern IO SST

Predictability in the NCEP coupled and uncoupled models - Model performance and correlation scores

- Relationship between the southern IO SST and ENSO in the NCEP CFS

General Conclusions

Outline Outline

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El-Nino

Seasonality of Asian Monsoons and ENSO Seasonality of Asian Monsoons and ENSO

Monsoons

Mature/Peak Decay Develop Mature

DJFDJF MAMMAM JJAJJA SONSON

Weak AuM Strong SAM

Weak SEAM Strong EAM

Spring p redicta

bility Spring p

redicta bility barrier

barrier

IOD Decay Develop Mature/Peak

Out-of-phase Out-of-phase

The direct impact of ENSO on the ASM; The direct impact of ENSO on the ASM;

Introduction – Indian Ocean SST and Asian Monsoon Introduction – Indian Ocean SST and Asian Monsoon

IO and Asian summer monsoon;IO and Asian summer monsoon;

-Ellis 1952; Saha 1970, 1974; Shukla 1975; Shukla and Misra 1977;Cadet and Diehl 1984;

Joseph and Phillai 1987; Meehl 1987; Joseph et al 1994; Li et al. 2001; Hendon 2003; etc.

Indian Ocean Dipole (IOD) – local ocean-atmoaphere coupled phenomenonIndian Ocean Dipole (IOD) –

South Asia (Ashok et al. 2001), East Asia (Saji and Yamagata 2003; Guan and Yamagata 2003), the Mediterranean, Australia, and even Brazil (Ashok et al. 2003a; Saji and Yamagata 2003)

Dependent vs. independent from the Pacific influence

Southern IO SST and monsoon; Southern IO SST and monsoon;

-Southern IO SST influences the Australian rainfall ( Nicholls 1989; Drosdowsky and Chambers 2001) and the variability of Asian summer monsoon (Zhu and Houghton 1996)

-Terray et al. (2003 and 2005) emphasized the role of SEIO for an ENSO-monsoon relationship.

- Yoo et al. (2006) showed SIO SST anomalies in the preceding spring are strongly associated with anomalous circulations over the western-northwestern Pacific in summer, a

relationship that is stronger than for SST in the north IO.

Southern IO SST;Southern IO SST;

– strongly influenced by tropical processes, such as ENSO (Behera and Yamagata 2001) and – Southern Annular Mode/Antarctic circumpolar wave (White and Peterson 1996; Peterson and White 1998; Huang and Shukla 2007, 2008)

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Precursors of ENSO Precursors of ENSO

The equatorial Pacific upper ocean heat content; The equatorial Pacific upper ocean heat content; Jin 1997; Meinen and McPhaden 2000

The local wind anomalies over the Western Pacific; The local wind anomalies over the Western Pacific; Weisberg and Wang 1997; McPhaden et al.

1998; Kug et al. 2005; Kug and Kang 2006

An important role in the phase transition from El-Nino to La-Nina phase transition from El-Nino to La-Nina through the Kelvin wave response (Weisberg and Wang 1997); Ohba and Ueda (2007) – possible role of IO SST on the ongoing El-Nino using CGCM

•Convergence of anomalous northerlies from the East Asian and southerlies over northeast of Australia induce sufficiently strong westerly anomalies over the WP; Xu and Chan (2001)

•IO SST play an important role for the variation of WP wind anomalies and Philippine anticyclonic; Watanabe and Jin 2002; Kug et al. 2005; Kug and Kang 2006; Yu et al. 2002; Wu and Kirtman 2004

Southern IO SST; Southern IO SST;

Terray et al. (2005) – SEIO as a common SST precusor of ENSO, Indian summer monsoon, Australian summer monsoon, IOD, and Maritime continent rainfall.

Objectives Objectives

 To find the dominant features of SST, precipitation, and large To find the dominant features of SST, precipitation, and large circulation patterns associated with Asian monsoon and different circulation patterns associated with Asian monsoon and different ENSO modes in summer.

ENSO modes in summer.

 To understand the relative importance of the Northern and Southern To understand the relative importance of the Northern and Southern IO for the Asian monsoon and ENSO.

IO for the Asian monsoon and ENSO.

 To suggest a possible processes and mechanisms explaining the To suggest a possible processes and mechanisms explaining the relationships between SIO SST, Asian monsoon, and ENSO.

relationships between SIO SST, Asian monsoon, and ENSO.

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Precipitation: CMAP data (2.5

x2.5

) SST: OISST (1

x1

)

850-mb Winds: NCEP/DOE Reanalysis 2 (2.5

x2.5

)

Atmospheric component: NCEP Global Forecasting System (GFS06, T62L64 )

Oceanic component: NOAA GFDL MOM3 Data (1982-2006)

Data (1982-2006)

NCEP Climate Forecasting System (CFS)

NCEP Climate Forecasting System (CFS)

Introduction

Possible role of IO SST in the Asian Monsoon and ENSO - Dominant features of Asian Monsoons and ENSO in summer

- Relative importance of Northern and Southern IO SST

Predictability in the NCEP coupled and uncoupled models - Model performance and correlation scores

- Relationship between the southern IO SST and ENSO in the NCEP CFS

General Conclusions

Outline

Outline

La-Nina Onset El-Nino Onset

EOF of JJA Precipitation Lead & Lag Correlation

Results - Observations Results - Observations

L H

JJA WY SAM SEAM EAM

P PC1 - - -0.73 -

P PC2 0.57 - 0.57 0.41

P PC3 - - - -

NINO3.4

SST -0.35 - 0.36 -

Out-of-phase!

ENSO Developing Mode ENSO Developing Mode

ENSO Decaying Mode ENSO Decaying Mode

Regression of 850-mb Wind & SST against EOF PCs of Precipitation

Correlation between EOF PCs & Monsoons

IOD IOD

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SST anomalies associated with the transition from El-Nino to La-Nina

Results - Observations Results - Observations SST anomalies associated with the El-Nino to Normal

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Regression of MAM MAM SST against JJA JJA Monsoon Indices

Introduction

Possible role of IO SST in the Asian Monsoon and ENSO - Dominant features of Asian Monsoons and ENSO in summer

- Relative importance of Northern and Southern IO SST

Predictability in the NCEP coupled and uncoupled models - Model performance and correlation scores

- Relationship between the southern IO SST and ENSO in the NCEP CFS

General Conclusions

Outline

Outline

ENSO Developing Mode ENSO Developing Mode

ENSO Decaying Mode

ENSO Decaying Mode

Regression of MAM MAM SST and EOF PCs of JJA JJA Precipitation

Results – NIO vs. SIO in Obs Results – NIO vs. SIO in Obs

EOF PC2

EOF PC1 SVD Modes between MAM MAM SST and JJA JJA

Precipitation

(Yoo et al., 2006 )

JJA

P PC1 P PC2 SAM SEAM NIO

Regression of JJA JJA 850-mb Wind and Precipitation against MAM MAM IO SST

MAM IO & JJA Wind, P

Results - NIO vs. SIO in Obs Results - NIO vs. SIO in Obs Lead & Lag Correlation between MAM IO SST PC1 & NINO3.4 SST

Time Series of EOF PC1 of MAM MAM IO SST & SON SON NINO3.4 SST

La-Nina Onset El-Nino Onset E

E E

E

L

L

L L

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Merid. Temp.

gradient bet. NIO

& SIO decrease

Strong cross- equatorial flow &

Somali Jet

weak cross- equatorial flow &

Somali Jet

C

A

C

Merid. Temp.

gradient bet. NIO

& SIO increase And bet. land- ocean decrease

A

A

A A

A C

NIO NIO SIO SIO

C

Walker Cir.Hadley Cir.

Anticyclonic Cir.

Cyclonic Cir.

Monsoon Flow

JJA Climatology of 850-mb wind JJA Climatology of 850-mb wind

Results - NIO vs. SIO in Obs Results - NIO vs. SIO in Obs

Composites of 850-mb Wind & Precipitation in summer

Clim Clim SIO minus NIO SIO minus NIO

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A large persistence of IO SST prior to the Asian summer monsoon provides a predictive potential of the monsoon across the spring predictability barrier, reinforcing the out-of-phase relationship between SAM and SEAM.

During the dissipation of El-Nino in spring, the SIO SST anomalies persist and are associated with SIO wave train from boreal winter.

Through the modulation of the monsoon flows from SIO to NIO, the SIO SST

anomalies in the preceding spring are strongly correlated with the easterly

(westerly) wind anomalies over WP, emergence of La-Nina (El-Nino) during

boreal summer.

Introduction

Possible role of IO SST in the Asian Monsoon and ENSO - Dominant features of Asian Monsoons and ENSO in summer

- Relative importance of Northern and Southern IO SST

Predictability in the NCEP coupled and uncoupled models - Model performance and correlation scores

- Relationship between the southern IO SST and ENSO in the NCEP CFS

General Conclusions

Outline

Outline

15 ensemble members

ICs of days 9-13, 19-23, and the last two days of the previous month and those of days 1-3 of the concurrent month

9-month integration per each hindcast runs

Climatological means of 1982-2006

Feb ICs Mar Apr May Jun Jul Aug Sep Oct Nov ; 9-month integration LM0 MAM

LM0 MAM LM3 JJA LM3 JJA LM6 SON LM6 SON

May ICs Jun Jul Aug Sep Oct Nov Dec Jan Feb LM0 JJA

LM0 JJA LM3 SON LM3 SON LM6 DJF LM6 DJF

1982 : : 2006

(Hindcast)

Results – NCEP Models Results – NCEP Models

SST Tendency (target season minus previous season)

Obs CFS

[LM3 minus LM0]

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SST Standard Deviation and 850-mb Winds CFS LM0 Obs

<

>

<

>

Results – NCEP Models Results – NCEP Models

Temporal Correlation Scores of NINO SSTs

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EOF 1^st mode of Indian Ocean SST Temporal Correlation Scores of IO SST

Results – NCEP Models Results – NCEP Models

Temporal Correlation Scores of Asian summer Monsoon

25/32

Introduction

Possible role of IO SST in the Asian Monsoon and ENSO - Dominant features of Asian Monsoons and ENSO in summer

- Relative importance of Northern and Southern IO SST

Predictability in the NCEP coupled and uncoupled models - Model performance and correlation scores

- Relationship between the southern IO SST and ENSO in the NCEP CFS

General Conclusions

Results – NCEP Models Results – NCEP Models

EOF 1^st mode of JJA Precipitation Regression of 850-mb Wind & SST

LM0 JJA

LM3 JJA

AMIP

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Lead & Lag Correlation Regression of MAMMAM SST against JJAJJA Precipitation LM0 JJA

LM3 JJA

AMIP

Results – NCEP Models Results – NCEP Models

Regression of MAMMAM SST against JJAJJA Monsoon Indices

LM0 JJA

LM3 JJA

AMIP

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Regression of JJAJJA 850-mb Wind & Precipitation

againt MAMMAM NIO/SIO SST SVD Modes between LM0 LM0 MAMMAM SST and LM3 LM3 JJAJJA Precipitation

NIO NIO SIO SIO

LM0 JJA

LM3 JJA

Results – NIO vs. SIO in the Models Results – NIO vs. SIO in the Models

Lead & Lag Correlation between LM0 MAM LM0 MAM IO SST PC1 & NINO3.4 SST

Excessive tropical zonal wind anomalies by ENSO-related SST

Delayed transition?

Delayed transition? (Wu et al., 2008) (Wu et al., 2008)

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An observed association between SIO SST anomalies and ENSO is unrealistically simulated in AMIP run.

Importance of ocean evolution consistent with air-sea interaction

The NCEP CFS successfully simulates many major features of precipitation and the interactive oceanic-atmospheric processes several months in

advance.

The relationship between SIO SST and WP precursor, the onset of ENSO

events is reasonably simulated although the excessive impact of ENSO

induce the delayed transition of the eastern equatorial pacific SST.

Schematic Diagram (SIO) Schematic Diagram (SIO)

150E

180E

DJF DJF

MAM MAM

JJA JJA

Pacific Ocean Pacific Ocean Indian Ocean

Indian Ocean

Walker Cir.Hadley

Cir.Monsoon Flow

Anticyclonic Cir.

Cyclonic Cir.

Basic Flow

A A

A

-Decrease convection over WP during El-Nino

->Anticyclonic cir. over SCS and NW of Australia (Rossby response) ->Weak Australian summer Monsoon

-Weaken & eastward movement of Walker Cir.

-SST gradient bet. IO & WP

->Easterly wind anomalies over WP ->Induce eastward tropical upward

Kelvin Wave ->El-Nino decays

-Strong easterly wind anomalies

->Anomalous Anticyclonic cir. over SCS

& local Had. Cir. Over NE of Australia

->Strengthen and extended subtropical western Pacific High

-> Weak SEA summer Monsoon -> La-Nina develops

-Weaken the clim. Anticyclonic cir. Over SIO during El-Nino

->Reduced evaporation over W of Australian ->Warm SST anomalies (Wind-evaporation

feedback )

-Southeastward wave propagation over SIO

-Eastward movement of SIO wave during El-Nino decays

->Phase-locked with SST anomalies over midlatitude SIO

->Cold SST anomalies over Southwest of SIO (Ekman pumping)

->Warm SST anomalies over Southeast of SIO (wind-evaporation

feedback)

-Decrease the merid. temp. grad. Bet. NIO &

SIO

->Weaken cross-equatorial flow & Somali Jet -Increase the zonal temp. grad. Bet.

Midlatitude SST anomalies ->Amplify clim. anticyclonic cir.

=>Moisture conv. Over TIO

-Persistent warm SST anomalies over NW of Australia

->Risist the northward shift of rainbands

=>Increase rainfall over Maritime Continents

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Thank you!

Thank you!