The flavor of El Nino in a changing climate

1. The flavor of El Nino in a changing climate 2010.11 Sang-Wook Yeh Hanyang University Colleagues: Jong-Seong Kug, Boris Dewitte, MinHo Kwon, Ben Kirtman, F.-F. Jin and Wonsun Park

2. :2009/10 El Nino NINO4 region NINO3 region Anomalous SST (Jan-Mar 2010) Base period: 1971-2000, Data source: NCEP, EMC

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

4. :A different flavor of El Nino

5. NINO4 region 1990/91 2009/10 El Nino 1991/92 1992/93 1993/94 Yu and Kim (2010) 1994/95

6. :A different flavor of El Nino II 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)

7. :A different flavor of El Nino III

8. :A different flavor of El Nino IV

9. Tropical-extratropical Teleconnection Influence on Other meteorological Phenomena (typhoon, monsoon, and North Pacific SST variability) A different flavor of El Nino Identification of Characteristics (seasonal evolution, subsurface structure and vertical structure….) Mechanism Global warming

10. Issues I • A different type of El Nino is a natural mode of SST variability or a new mode of SST variability?

11. (Guan and Nigam, 2008, Journal of Climate)

12. Composite of different flavor of El Nino events Time

13. 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)

14. Issues II • Why such a different flavor of El Nino occurs more frequently during recent decades?

15. :EP (Eastern Pacific) El Nino: Conventional El Nino : CP (Central Pacific) El Nino: A different flavor of El Nino 2009 2009

17.  Global warming 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

18. 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).

19. Kiel Climate Model (Park et al. 2009, Journal of climate)  No flux correction  4200 years simulation period

20.  Natural variability - Kiel Climate Model (4200 years) - Observation (60 years, 1950-2009)

21.  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

22.  Natural variability 30 years in the KCM 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. 1.38 0.26 Mean ratio: 0.82 One standard deviation: 0.56

23.  Further issue

24. :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)

25. :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

26. :How do we define a different flavor of El Nino? • Statistical methodology (EOF, REOF….) • NINO indices

27. Thank you

29.  Mechanism Thermocline feedback process Zonal advective feedback process - Thermocline depth flattening ~ reduces upwelling ~ reduce thermocline feedback process - Vertical displacement of thermocline depth in the central Pacific

30.  Natural variability - Kiel Climate Model (4200 years)

31.  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.

32.  Mechanism (Vecchi et al. 2006, Nature) 1979-2004 minus 1958-1978 (Ashok et al. 2007, JGR)

33. If the wind gets a little bit weaker ….. Δ wind -> Δ upwelling -> Δ SST Wind α (warm minus cold) warm wind wind Less cold warm cold thermocline thermocline West East West East Wind α (warm minus Less cold) -> Even weaker wind • El Nino 연구: The early 1980s ~ the mid 1990s • Theoretical understanding of the mechanisms for the ENSO cycle

34.  Mechanism Thermocline feedback process Zonal advective feedback process • Shallow thermocline depth tends to dominate the zonal advective feedback process in the central Pacific (Bejarano and Jin 2008)

36. Changes in mean field W C

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