Transcript El Nino - Clivar

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
:2009/10 El Nino
NINO4 region
NINO3 region
Anomalous SST (Jan-Mar 2010)
Base period: 1971-2000, Data source: NCEP, EMC
..When did we pay attention to a different flavor of El
Nino?
:A different flavor of El Nino
Author
Trenberth and
Hoar (1996)
Main point
- The 1990-1995 ENSO event
Remark
- No terminology
is used
….In the traditional El Nino region, SSTAs
have waxed and waned, while SSTAs in the
central equatorial Pacific remains positive
from 1990 to 1995….
Latif et al.
(1997)
- Understand the anomalous 1990s
- No terminology
is used.
Goddard and
Graham (1997)
- El Nino in the 1990s
- No terminology
…It is shown that the warm episodes of the is used
1990s differ from previous El Niños in two
important ways. …. ….Second, a persistent
warm SST anomaly in the central Pacific…..
NINO4 region
1990/91
2009/10 El Nino
1991/92
1992/93
1993/94
Yu and Kim (2010)
1994/95
:A different flavor of El Nino II
Author
Main point
Remark
Larkin and
- The seasonal weather anomalies over
Harrison (2005) 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)
- El Nino
Modoki
- Anomalous warming events in the
central Pacific (El Nino Modoki) which
differently influence the climate
compared to the conventional El Nino
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 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
 Influence on
Other meteorological
Phenomena
(typhoon, monsoon,
and North Pacific
SST variability)
 Tropical-extratropical
Teleconnection
A different flavor
of El Nino
 Mechanism
 Global warming
 Identification of
Characteristics
(seasonal evolution,
subsurface structure
and vertical
structure….)
 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
 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
- 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 (Park et al. 2009, Journal of climate)
 No flux correction
 4200 years simulation period
 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
30 years in the KCM
1.38
Mean ratio: 0.82
One standard deviation: 0.56
0.26
HadISST
19501979
19802009
CP/EP
ratio
0.14
0.42
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.
 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
Zonal advective feedback process
Thermocline feedback process
T 
T
T 
 u

t
x
z
- Thermocline depth flattening ~ reduces upwelling ~
reduce thermocline feedback process
- Vertical displacement of thermocline depth in the central Pacific
 Natural variability
- Kiel Climate Model (4200 years)
CP El
Nino
Kiel
625
Climate
Model
EP El
Nino
CP El Nino
/ EP El Nino
819
0.76
 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
(Vecchi et al. 2006, Nature)
1979-2004 minus 1958-1978
(Ashok et al. 2007, JGR)
El Nino 연구: The early 1980s ~ the mid 1990s
-Theoretical understanding of the mechanisms for the ENSO
cycle
If the wind gets a little bit weaker …..
Wind α (warm minus cold)
warm
Δ wind -> Δ upwelling -> Δ SST
wind
warm
cold
West
East
West
wind
Less cold
East
Wind α (warm minus Less cold) -> Even weaker wind
 Mechanism
Zonal advective feedback process
Thermocline feedback process
T 
T
T 
 u

t
t
t
-Shallow thermocline depth tends to dominate the zonal advective
feedback process in the central Pacific (Bejarano and Jin 2008)
W
C
Changes
in mean
field
:Mechanism
Global
Warming
Changes
in mean
field
Enhance
Natural
mode
Changes in zonal
mean SST gradient
T 
T
T 
 u

t
x
z
“A different flavor
of El Nino”