changes in the enso (el nino) spatial structure in ... · changes in the enso (el nino) spatial...

Changes in the ENSO (El Nino) spatial structure in relation to the PDO in the CMIP5

Sang-Wook Yeh Hanyang University

• ENSO Diversity

Yeh et al. (2009)

• Changes in El Nino spatial structure

• ENSO Diversity : CP El Nino & EP El Nino

McMcPhaden et al. (2009)

Sohn et al. (2012) 1999-2008 minus 1979-1998

Before the late 1990 After the late 1990

Before the late 1990 After the late 1990

PDO index

• Mechanism of frequent occurrence of CP El Nino

.. the recent predominance of standing CPW(Central Pacific Warming) arises from a dramatic decadal change characterized by a grand La Nina-like background pattern and strong divergence in the central Pacific atmospheric boundary layer…(Xiang et al. 2012) ..Mean state change (i.e., a cooling (warming) over tropical eastern (western) Pacific) is associated with more frequent occurrence of CP El Nino during 1999-2010…A shift to the La Nina-like interdecadal mean state is responsible for more frequent occurrence of CP-type El Nino…(Chung and Li, 2013)

• Question

…Are there any connections between a phase of PDO and the changes in the spatial structure of El Nino ?

Model # Model

1 CanESM2

2 CCSM4

3 CESM1-CAM5

4 CNRM-CM5

5 CSIRO-Mk3-6-0

6 GISS-E2-R

7 HadGEM2-ES

8 IPSL-CM5A-LR

9 MPI-ESM-LR

10 NorESM1-M

- Historical run: 1905-2005 - RCP 4.5 run: 2100-2200


- Analyzed CGCMs in CMIP5

• Composite analysis : El Nino & PDO phase

•  El Nino: 0.5°C < NINO3.4 SST Index during winter • Positive PDO phase: EOF1 SST PC (North Pacific) during winter > 0 • Negative PDO phase: EOF1 SST PC (North Pacific) during winter < 0

Winter (December-January-February, DJF)

• El Nino + Positive PDO phase

Historical run

RCP4.5 run RCP4.5 run

minus Historical run (C.I.:0.1°C)

• El Nino + Negative PDO phase

Historical run

RCP4.5 run

:

RCP4.5 run minus

Historical run (C.I.:0.1°C)

• Composite analysis : El Nino & PDO phase

•  El Nino: 0.5°C < DJF NINO3.4 SST Index < 1.0 ° C: Moderate El Nino •  El Nino: 1.0 °C < DJF NINO3.4 SST Index : Strong El Nino •  Positive PDO phase: EOF1 SST PC (North Pacific) during winter > 0 •  Negative PDO phase: EOF1 SST PC (North Pacific) during winter < 0

:Moderate El Nino + Positive PDO phase

:Moderate El Nino + Negative PDO phase

• Moderate El Nino

Historical run RCP4.5 run

• Moderate El Nino

: Moderate El Nino + Positive PDO phase

: RCP4.5 run minus Historical run : Moderate El Nino + Negative PDO phase

: RCP4.5 run minus Historical run

• Strong El Nino

:Strong El Nino + Positive PDO phase

:Strong El Nino + Negative PDO phase


• Strong El Nino

: Strong El Nino + Positive PDO phase



: Strong El Nino + Negative PDO phase


…. It is found that there exist the changes in spatial structure of El Nino under a negative phase of PDO (mostly due to moderate El Nino ) from the Historical run to the RCP 4.5 run…

Historical run

RCP4.5 run

A shift of a center of maximum anomalous SST from the

east to the west

• Questions

: Why a negative phase of PDO matters ? : Why the moderate El Nino is sensitive to change its spatial structure under global warming (i.e., RCP4.5 run)?

• Why a negative phase of PDO matters ?

: Hypothesis : A negative phase of PDO under global warming (i.e., RCP4.5 run) provides more favorable condition to change the spatial structure of moderate El Nino (i.e., a shift of center of maximum anomalous SST to the west)

• A negative phase of PDO I

• Ensemble mean SST composite of a negative phase of PDO in the Historical run & RCP4.5 run


• An enhancement of zonal advective feedback processes

• A negative phase of PDO II

RCP4.5 run minus Historical run: A negative phase of PDO

Suppress the air-sea coupling strength in the eastern Pacific

A shift of the anomalous convection and zonal wind response westward

Cause the anomalous convection confined in the western and central Pacific

Enhancement of anomalous SST in the western and central Pacific

• Why the moderate El Nino not Strong El Nino?

: Hypothesis : - The main mechanism for the moderate El Nino and strong El Nino is different. - The moderate El Nino may be more associated with zonal advective feedback processes than thermocline feedback processes.

-  Therefore, moderate El Nino is more sensitive to change its spatial structure under the change of a negative phase of PDO in the RCP4.5 run, which largely influences the zonal advective feedback processes.

• Fundamental question

• Why the current La Nina-like background pattern (i.e., Negative phase of PDO) plays a role to induce more frequent occurrence of CP El Nino in comparison with a previous La Nina-like background period?

Previous La Nina-like b

ackground

Current La Nina-like Background

Historical run

RCP4.5 run

Thank you

• Future changes in El Nino spatial structure

• Ensemble mean in the Historical run:

: La Nina + Positive PDO phase

: La Nina + Negative PDO phase

Historical run


• Changes in ENSO spatial structure

RCP4.5

: La Nina+ Positive PDO phase : La Nina+ Negative PDO phase

• El Nino: EOF1 PC (Tropical Pacific) >0.5S.D. • Positive PDO phase: EOF1 PC (North Pacific) > 0.5 S.D. • Negative PDO phase: EOF1 PC (North Pacific) < -0.5 S.D

: Composite analysis : El Nino & PDO phase

• Ensemble mean in the Historical run:


: El Nino + Positive PDO phase

: El Nino + Negative PDO phase

• Ensemble mean in the RCP4.5


: El Nino + Positive PDO phase

: El Nino + Negative PDO phase

Historical run


• Changes in ENSO spatial structure

RCP4.5 run

: El Nino + Positive PDO phase : El Nino + Negative PDO phase

8 models Ensemble except CSIRO-Mk3-6-0 and GISS-E2-R

• Pacific Decadal Oscillation & ENSO - observation

-EP El Nino years :1957/58, 1965/66, 1972/73, 1976/77, 1982/83, 1986/87, 1991/92, 1997/98 -CP El Nino years :1958/59,1968/69,1987/88, 1990/91, 1994/95, 2002/03, 2004/05, 2009/10

-HadISST, 1950-2011, Detrend SST data -[CP & EP El Nino: Ren and Jin (2011), PDO: EOF1 PC in the North Pacific] -Red (Positive phase PDO), Blue (Negative Phase PDO)

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