Download G163S10L15_enso_ROD

El Niño/Southern Oscillation
• Major climatic perturbation on the planet
• Coupled atmosphere ocean process
• Key is the western tropical Pacific
– Ascending branch of the Walker circulation
– Potential energy for Kelvin wave pulse
• www.pmel.noaa.gov/tao/elnino/nino-home.html
The Southern Oscillation
• Discovered in 1928
by Sir Gilbert Walker
• Links D’s in global
climate indices
• Proposes a zonal
circulation cell over
the equatorial Pacific
The Southern Oscillation
The Southern Oscillation
• Pressure D’s regulate strength of the trades
• El Niño periods = weak trades
Southern Oscillation Index
• SOI = Tahiti - Darwin air pressure D’s
• Low SOI = El Niño conditions
Southern Oscillation
Nino Regions
Multivariate ENSO Index
• Combines observations of air pressure, zonal &
meridional components of wind, sea surface
temperature, air temperature and total cloudiness.
• Positive MEI = ENSO conditions
Walker Circulation
• East-to-west pressure gradients drive trades
Walker Circulation
• Vertical cell driven by warmest waters
Western Pacific Warm Pool
Coupled Walker/Ocean
Circulation
Coupled Walker/Ocean
Circulation
El Niño
Events
• Relaxation of
trades causes
warm pool to
slosh across
Pacific basin
El Niño Conditions
El Niño Conditions
La Nina
• Opposite phase of the
ENSO cycle
• Intensified trades &
Walker circulation
• Thermocline undergoes
maximum upwelling
EL NIÑO/SOUTHERN OSCILLATION
(ENSO)
DIAGNOSTIC DISCUSSION
issued by
CLIMATE PREDICTION CENTER/NCEP
10 May 2010
A transition from El Niño to ENSO-neutral is underway.
Sea surface temperatures are decreasing across much of the Pacific
Ocean.
Based on current observations and dynamical model forecasts, a
transition to ENSO-neutral conditions is expected by June 2010,
which will continue into the Northern Hemisphere summer 2010.
Although most models predict ENSO-neutral conditions, there is a
growing possibility of La Niña developing during the second half of
2010.
Today…
Today…
Altimetry &
ENSO States
• Most “action” is in the
tropical Pacific
• Effects are seen in
other places
– East subtropics
– Western NECC region
Effects of an El Niño
• Region of ascending air
has moved to center of
equatorial Pacific
• Climate system shifts
over 10,000 km to east
• Affects the entire planet
An El Niño History
• late 1800s Fishermen name El Niño to the
periodic warm waters that appear off the coasts of
Peru and Ecuador around Christmas.
• 1928 Gilbert Walker describes the Southern
Oscillation.
• 1957 A large El Niño is observed which affects not
just the coasts of Peru and Ecuador but the entire
Pacific Ocean.
• 1969 Jacob Bjerknes links the Southern Oscillation
with El Niño events.
An El Niño History
• 1975 Wyrtki uses island sea level to show how
eastward flow causes SST’s to rise in east Pacific.
• 1976 An idealized computer model demonstrates
that winds over the far western Pacific can change
SST off Peru.
• 1982 A severe El Niño develops unexpectedly, but
is recorded in detail with newly developed ocean
buoys.
• 1985 Several nations launch the Tropical OceanGlobal Atmosphere (TOGA) program.
An El Niño History
• 1986 First coupled model of ocean & atmosphere
predicts El Niño event.
• 1988 Researchers explain how the "memory" of the
ocean--the lag between a change in the winds and
the response of the ocean--influences terminations
of El Niño and the onset of La Niña.
• 1996-1997 The array of instruments monitoring the
Pacific, plus coupled ocean-atmosphere models,
enable scientists to warn the public of an impending
El Niño event.
Coupled Walker/Ocean
Circulation
El Niño Conditions
Effects of an El Niño
• Places that were wet are now dry and vice versa
Effects of an El Niño
El Niño in
Australia
El Niño in Australia
Teleconnections
• Discovered in 1928
by Sir Gilbert Walker
• Links D’s in global
climate indices
• Proposes a zonal
circulation cell over
the equatorial Pacific
El Niño
• Hadley cells intensify as source of heat is now in
central equatorial Pacific
• Jet stream intensifies & takes south path
El Niño in the United States
El Niño in the United States
El Niño in the United States
El Niño in the United States
El Niño & Hurricane Damage
El Niño & Hurricane Damage
El Niño & Diseases
Delayed Oscillator Theory
• Seeds of El Nino destruction as it starts...
Delayed Oscillator Theory
Delayed Oscillator Theory
El Niño Conditions
97-98 El Niño Event
97/98 El Niño
• At its peak, the 97/98 El Niño was biggest
of all time
97/98 El Niño
97/98
El Niño
97/98 El Niño
• TOPEX/Poseidon sea level anomaly December 1, 1997
97/98 El Niño
97/98 El Niño
OLR = outgoing longwave energy (high OLR = no clouds)
97/98 El Niño
97/98 El Niño Movie
More readings
• NOAA ENSO Page
www.pmel.noaa.gov/tao/elnino/nino-home.html
• Review of 97/98 El Nino
www.icess.ucsb.edu/~davey/Geog163/950.pdf