Lesson 11: El Niño Southern Oscillation (ENSO) Physical Oceanography
The Two Types of ENSO - usclivar.orgthe EP El Niño but interacts with the Hadley circulation to...
Transcript of 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)
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Possible Forcing Mechanisms for CP ENSO
Monsoon
forcing
Extra-tropical
forcing
CP ENSO
(Yu et al. 2009)
(Yu et al. 2010)
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CP-ENSO SST Variations
-14
-4
-10
-6
-12
-8
+2 0 -2
(Yu, Kao, and Lee 2010)
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North Pacific Oscillation (NPO) and Associated SST
Anomalies
EO
F2
SST
NPO (SLP EOF mode) Correlated SST
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NPO-Correlated SSTA Evolution
lag-0 Lag+2 Lag+4
+6 +8 +10
+12 +14 +16
(Yu and Kim 2011)
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Three Evolution Patterns for CP El Nino
mean thermocline depth at equator
Prolonged Decay
Abruptly Decay
Symmetric Decay
(Yu and Kim 2010)
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Transitions between CP and EP ENSOs
NPO
CP EP
Equatorial Thermocline
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EP/CP-ENSO Correlates with SLP
EP ENSO
CP ENSO
Hadley Circulation
Walker Circulation
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Walker and Hadley Circulations
Equator
20-30N
CP EP
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When Walker Circulation Is Stronger…
Equator
20-30N
EP El Niño
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NPO
When Hadley Circulation Is Stronger…
Equator
20-30N
CP El Niño
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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.
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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)
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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)
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ENSO SST Anomalies Prescribed for the AGCM (CAM4) Experiment
EP El Niño CP El Niño
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Case Studies with EP/CP El Niño Events Strong EP
Events Strong CP
Events
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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)
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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
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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
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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.