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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
: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
: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?
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)
: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
- 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
: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
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.
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
: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”
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