The flavor of El Nino in a changing climate

Sang-Wook YehHanyang University

2010.11

Colleagues: Jong-Seong Kug, Boris Dewitte, MinHo Kwon, Ben Kirtman, F.-F. Jin and Wonsun Park

:2009/10 El Nino

Base period: 1971-2000, Data source: NCEP, EMC

Anomalous SST (Jan-Mar 2010)

NINO4 region NINO3 region

..When did we pay attention to a different flavor of El Nino?

:A different flavor of El Nino

Author Main point Remark

Trenberth and Hoar (1996)

- The 1990-1995 ENSO event

….In the traditional El Nino region, SSTAs have waxed and waned, while SSTAs in the central equatorial Pacific remains positive from 1990 to 1995….

- No terminology is used

Latif et al. (1997)

- Understand the anomalous 1990s - No terminology is used.

Goddard and Graham (1997)

- El Nino in the 1990s…It is shown that the warm episodes of the 1990s differ from previous El Niños in two important ways. …. ….Second, a persistent warm SST anomaly in the central Pacific…..

- No terminology is used

Yu and Kim (2010)

2009/10 El Nino

NINO4 region

1990/91

1991/92

1992/93

1993/94

1994/95

:A different flavor of El Nino II

Author Main point Remark

Larkin and Harrison (2005)

- The seasonal weather anomalies over the U.S associated with the dateline El Nino season substantially different from those associated with conventional El Nino seasons.

- Dateline El Nino

Ashok et al. (2007)

- Anomalous warming events in the central Pacific (El Nino Modoki) which differently influence the climate compared to the conventional El Nino

- El Nino Modoki

A new NOAA definition of El Nino: A positive SST departure from normal (1971-2000) in the NINO3.4 region greater than or equal in magnitude to 0.5C, averaged over three consecutive months)

:A different flavor of El Nino III

Author Main point Remark

Kao and Yu (2009)

- Physically identify the two different types of El Nino in terms of structure, evolution and teleconnections

- Eastern Pacific El Nino & Central Pacific El Nino

Kug et al. (2009)

-Physically identify the two different types of El Nino in terms of transition mechanism and its associated dynamics (Zonal advective feedback versus thermocline feedback)

- Cold tongue El Nino & Warm Pool El Nino

:A different flavor of El Nino IV

Author Main pointTrenberth and Smith (2006) - Vertical structure of Temperature in different flavors of El Nino

Wang and Hendon (2007) - Influence of two types of El Nino in Australia

Weng et al. (2007) - Teleconnections in the Pacific between the two types of El Nino

Trenberth and Smith (2009) - Identify the three dimensional structure of the atmospheric circulation with different flavors of El Nino

Yeh et al. (2009) - Two types of El Nino and global warming

Kim et al. (2009) - Atlantic Hurricane activity between the two types of El Nino

Kug et al. (2010) - Long term analysis of two types of El Nino in a CGCM

Chen and Tam (2010) - North Pacific typhoon activity between the two types of El Nino

Yu and Kim (2010a) - Evolution patterns of Central Pacific El Nino

Yu et al. (2010b) - Subsurface Ocean structure in two types of El Nino

Yu and Kim (2010c) - Identification of two types of El Nino in a CMIP3 model

Yu et al (2010d) - Relationship with the extratropcial variations

Yu et al (2010e) - Relationship with the subtropical Pacific SST variability

Di Lorenzo et al. (2010) - Influence of Central Pacific El Nino to the North Pacific

Lee and McPhaden (2010) - Relationship between mean state changes and an increase of Central Pacific El Nino

A different flavorof El Nino

Tropical-extratropical Teleconnection

Influence on Other meteorological Phenomena(typhoon, monsoon,and North Pacific SST variability)

Mechanism

Identification of Characteristics (seasonal evolution, subsurface structureand vertical structure….) Global warming

Issues I

- A different type of El Nino is a natural mode of SST variability or a new mode of SST variability?

(Guan and Nigam, 2008, Journal of Climate)

Composite of different flavor of El Nino events

Time

The noncanonical ENSO mode is one of natrual variability in the Pacific SSTs in the 20th century

The noncanonical ENSO mode is energetic in recent decades…

The noncanonical ENSO mode is characterized by eastward development of positive SST anomalies along the equator, beginning with the central Pacific ones.

(Guan and Nigam, 2008, Journal of Climate)

Issues II

- Why such a different flavor of El Nino occurs more frequently during recent decades?

:EP (Eastern Pacific) El Nino: Conventional El Nino

: CP (Central Pacific) El Nino:A different flavor of El Nino

2009 2009

As anthropogenic global warming intensifies, we may see more of these events compared to the conventional El Nino (Yeh et al. 2009)

20C3M: 20th century climate change simulation

SRESA1B: The climate change run following the SRESA1B scenario

Global warming

- One critical issue is whether the modal shift of Central Pacific El Nino is a just a manifestation of natural climate variability on decadal to centennial timescales (Ashok and Yamagata 2009).

Kiel Climate Model

No flux correction

4200 years simulation period

(Park et al. 2009, Journal of climate)

Natural variability

- Kiel Climate Model (4200 years)

- Observation (60 years, 1950-2009)

Natural variability

- Central Pacific El Nino/Eastern Pacific El Nino = 0.28 (60 years in the observation)

- Central Pacific El Nino/Eastern Pacific El Nino = 0.71 (4200 years in the KCM)

60 years in the KCM

Mean

Natural variability

One may consider that the variation of the ratio between 0.26 and 1.38 in the range of plus and minus one standard deviation is within a natural variability.

This indicates that five times increase of the ratio from one period of 30 years to other period of 30 years could be considered as a natural variability.

HadISST 1950-1979

1980-2009

CP/EP ratio

0.14 0.42

30 years in the KCM

Mean ratio: 0.82

One standard deviation: 0.56

1.38

0.26

Further issue

:Model evaluation for a different type of El Nino

…TNI (Trans-Nino Index) should also be examined in evaluating models to determine the extent to which the different flavors of ENSO are captured…….(Trenberth and Stepaniak 2001)

:Model evaluation for a different type of El Nino

Characteristics (Evolution, Transition, Spatial pattern, Intensity and associated vertical structure)

Tropical-Extratropical Teleconnection

Relationship with other meteorological phenomena

:How do we define a different flavor of El Nino?

Statistical methodology (EOF, REOF….)

NINO indices

Thank you

Mechanism

z

T

x

Tu

t

T

Thermocline feedback process

- Thermocline depth flattening ~ reduces upwelling ~ reduce thermocline feedback process

- Vertical displacement of thermocline depth in the central Pacific

Zonal advective feedback process

Natural variability

CP El Nino

EP El Nino

CP El Nino / EP El Nino

Kiel Climate Model

625 819 0.76

- Kiel Climate Model (4200 years)

Natural variability

The ratio increases as much as 3.5 times.!

The ensemble mean ratio increases as much as 1.7 times from the 20C3M run to the SRESA1B run.

Mechanism

1979-2004 minus 1958-1978

(Ashok et al. 2007, JGR)

(Vecchi et al. 2006, Nature)

El Nino 연구 : The early 1980s ~ the mid 1990s

-Theoretical understanding of the mechanisms for the ENSO cycle

warm

cold

Wind α (warm minus cold)

wind

thermocline

West East

warm wind

Δ wind -> Δ upwelling -> Δ SST

Less cold

thermocline

Wind α (warm minus Less cold) -> Even weaker wind

West East

If the wind gets a little bit weaker …..

Mechanism

t

T

t

Tu

t

T

Thermocline feedback process

-Shallow thermocline depth tends to dominate the zonal advective feedback process in the central Pacific (Bejarano and Jin 2008)

Zonal advective feedback process

Changes in mean

fieldW C

:Mechanism

Global Warming

Changes in mean

field

EnhanceNatural mode

Changes in zonal mean SST gradient

z

T

x

Tu

t

T

“A different flavorof El Nino”