the two types of enso - usclivar.orgthe ep el niño but interacts with the hadley circulation to...
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The Two Types of ENSO
Central-Pacific El Niño (related to atmospheric forcing)
Eastern-Pacific El Niño (related to thermocline variation)
(Yu and Kao 2007; Kao and Yu 2009)
Possible Forcing Mechanisms for CP ENSO
Monsoon
forcing
Extra-tropical
forcing
CP ENSO
(Yu et al. 2009)
(Yu et al. 2010)
CP-ENSO SST Variations
-14
-4
-10
-6
-12
-8
+2 0 -2
(Yu, Kao, and Lee 2010)
North Pacific Oscillation (NPO) and Associated SST
Anomalies
EO
F2
SST
NPO (SLP EOF mode) Correlated SST
NPO-Correlated SSTA Evolution
lag-0 Lag+2 Lag+4
+6 +8 +10
+12 +14 +16
(Yu and Kim 2011)
Three Evolution Patterns for CP El Nino
mean thermocline depth at equator
Prolonged Decay
Abruptly Decay
Symmetric Decay
(Yu and Kim 2010)
Transitions between CP and EP ENSOs
NPO
CP EP
Equatorial Thermocline
EP/CP-ENSO Correlates with SLP
EP ENSO
CP ENSO
Hadley Circulation
Walker Circulation
Walker and Hadley Circulations
Equator
20-30N
CP EP
When Walker Circulation Is Stronger…
Equator
20-30N
EP El Niño
NPO
When Hadley Circulation Is Stronger…
Equator
20-30N
CP El Niño
El Niño shifted from EP to CP (Yu, Lu, and Kim 2012)
Walker Circulation
before 1990 after
1990
Wal
ker
Cir
cula
tio
n S
tren
gth
(×
10
-1
Pa/s
ec)
Hadley Circulation
before 1990
after 1990
Had
ley
Cir
cula
tio
n S
tren
gth
(m
/sec
)
EP
before 1990
after 1990
NPO
CP
The increased extratropical forcing to the tropics after 1990
is a likely cause for the recent emergence of the Central-
Pacific El Niño.
Regressed US Winter (JFM) Temperature
NE
SW
NW
SE
With EP El Niño Index With CP El Niño Index
(1948-2010)
(Yu, Zou, Kim, and Lee, 2012)
Ensemble Forced AGCM Experiments
NCAR CAM4 Forced by the SST from
EP ENSO SSTA + Climatology CP ENSO SSTA + Climatology
(Yu, Zou, Kim, and Lee 2012)
ENSO SST Anomalies Prescribed for the AGCM (CAM4) Experiment
EP El Niño CP El Niño
Case Studies with EP/CP El Niño Events Strong EP
Events Strong CP
Events
Regressed US Winter (JFM) Precipitation
With EP El Niño Index With CP El Niño Index
CP Impact – EP Impact
CP El Niño enhances dry anomalies & weakens wet anomalies More droughts in the US
(Yu and Zou 2013)
Precipitation Anomalies during El Niño Winters
mean:6.7
mean:6.6
mean:1.5 mean:-4.3 mean:0.8
mean:-10.3
mean:4.2 mean:12.4
EP CP
EP
EP
EP
CP
CP
CP
Different Impacts of the Two Types of ENSO on US winter
Enhanced Drying Effects 90° Rotation of the Impacts
US Winter Temperature US Winter Rainfall
Summary • There may exist two distinct types of El Niño: an Eastern-Pacific type
and a Central Pacific type.
• Tropical Pacific Ocean interacts with the Walker circulation to produce
the EP El Niño but interacts with the Hadley circulation to produce the
CP El Niño.
• The increased influence from extratropial atmosphere over tropical Pacific is a likely cause for the shift of El Niño from the Eastern-Pacific type to the Central-Pacific type since 1990.
• The impacts produced by the Central-Pacific and Eastern-Pacific types of El Niño on US winter climate are different.
• The increasing occurrence of the CP El Niño in the recent decades may have also contributed to the US drought conditions.