The flavor of El Nino in a changing climate Sang-Wook Yeh Hanyang University Colleagues: Jong-Seong Kug, Boris Dewitte, MinHo Kwon, Ben Kirtman, F.-F. Jin and Wonsun Park

:2009/10 El Nino Base period: , Data source: NCEP, EMC Anomalous SST (Jan-Mar 2010) NINO4 regionNINO3 region

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

:A different flavor of El Nino AuthorMain pointRemark Trenberth and Hoar (1996) - The 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/ / / / /95

:A different flavor of El Nino II AuthorMain pointRemark 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 ( ) 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 AuthorMain pointRemark 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 AuthorMain point Trenberth 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 flavor of El Nino  Tropical-extratropical Teleconnection  Influence on Other meteorological Phenomena (typhoon, monsoon, and North Pacific SST variability)  Mechanism  Identification of Characteristics (seasonal evolution, subsurface structure and 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 20 th 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

As anthropogenic global warming intensifies, we may see more of these events compared to the conventional El Nino (Yeh et al. 2009) 20C3M: 20 th 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, )

 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 CP/EP ratio years in the KCM Mean ratio: 0.82 One standard deviation: 

 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 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 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 minus (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 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 field WC

:Mechanism Global Warming Changes in mean field Enhance Natural mode Changes in zonal mean SST gradient “A different flavor of El Nino”