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ENSO Prediction and Policy. Why Predict ENSO? How do we predict ENSO? Why is it possible ? What information do predictions offer? What to do with this information? An on-the-ground policy application…. Why does ENSO State tend to Oscillate?. Equatorial ocean dynamics - PowerPoint PPT Presentation
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ENSO Prediction and Policy
• Why Predict ENSO?
• How do we predict ENSO?
• Why is it possible ?
• What information do predictions offer?
• What to do with this information?
• An on-the-ground policy application…
Why does ENSO State tend to Oscillate?
Equatorial ocean dynamicsKey observations by Klaus Wyrtki in 1970’sEl Nino is preceded by a transfer of warm water
from west to eastThis transfer is thought to trigger a warm eventWhat triggers the movement of water?
– In cold phase, waters cold (and low) in east, warm (and high) in west
– Warm water from west sloshes back and overshoots equilibrium- positive feedbacks mentioned before set of El Niño conditions
Why does ENSO State tend to Oscillate?
Shortest Answer: Equatorial ocean dynamics
Short answer: Differing timescales of Kelvin and Rossby Wave propagation
Longer answer: The oscillation is made possible due to the asymmetry between eastward and westward oceanic motions (see 2-D Animation in notes).
Along the equator there is a relatively fast eastward motion called an equatorial Kelvin wave. Peaking somewhat off the equator are westward motions called Rossby waves. Time scale: <1 yr for the Kelvin waves to shift the warm pool eastward [once trades relax]; 2 yrs for the Rossby waves to return the warm pool to the west, to await another wind relax.
KelvinRossby
Here is a 3-D animation the tropical Pacific as it cycles through an El Niño then La Niña event. The surface shown is sea-level (in cm) and the surface is colored according to the SST anomalies associated with each event.
Normal Conditions in the tropical Pacific
Sea level pressureSea surface temperaturesTrade winds Walker circulationEquatorial upwellingThermocline depthSea surface heightTropical rainfall patterns
El Niño Conditions
Sea level pressureSea surface temperaturesTrade winds Walker circulationEquatorial upwellingThermocline depthSea surface heightTropical rainfall patterns
La Niña Conditions
Sea level pressureSea surface temperaturesTrade winds Walker circulationEquatorial upwellingThermocline depthSea surface heightTropical rainfall patterns
What’s going to happen?
Forecasts courtesy of IRI (Lamont-Doherty)
SSTanomalies this week (5-11 Oct. 2014)
What will next week/month/quarter look like?
?
Hawaii DroughtIndonesia Flooding
Societal impact of ENSO in the news
2010 news…
How ENSO impacts people
Effective management of climate related risks (opportunities) for improved:
• Agricultural production– Stocking, cropping calendar, crop selection, irrigation, insurance,
livestock/trade
• Water resource management– Dynamic reservoir operation, power generation, pricing/insurance
• Food security– Local, provincial, regional scales
• Public health– Warning, vaccine supply/distribution, surveillance measures,…
• Natural resource management– Forests/fire, fisheries, water/air quality
• Infrastructure development
Month
JULMAYMARJANNOVSEP
200
100
0
Rainfall (mm)
Malaria incidence
The disease is highly seasonal and follows the rainy season with a lag of about 2 months
Malaria and Rainfall
ENSO and Zimbabwe corn yield
+
-
ENSO
Predictions and PolicySnapshots of current conditions
are not very useful.
People need advance warning, and for their region.
Today:
1) how predictions are made
2) what we can do with them
ENSO Prediction Methods
• Skillful 6-9 months into the future• This ability has saved many millions of lives• Two methods: Dynamical vs. Statistical
El Niño Forecasting
Stephen E. ZebiakSenior Research Scientist
International Research Institute for Climate Prediction
Mark CaneDEES
Vetlesen Professor
Real Time Ocean ObservationsARGO floats
XBT (eXpandable BathiThermograph)
Moorings
Satellite
SST
Sea Level
M.A. Balmaseda ( ECMWF)
ARGO drift sensors
TOGA TAO mooring array
M.A. Balmaseda ( ECMWF)
Surface layer
Deep ocean; u=v=w=0
Active layer
50 m
150 m
Simplified Ocean and Atmosphere Models
Simplified form of equations for conservation of mass, momentum, energy
SSTA
Tropopause
Climate Models
Winds,Heatfluxes
Ocean simulation
Ocean obs.
Ocean analysis
t t + t
SST forcing
Atmos. simulation
Atmos. obs.
Atmos. analysis
t t + t
Data assimilation
Initial Conditions, t=t0
Atmosphere model Ocean model
FORECAST
Forecast Initialization Procedures
Modeling gives you skill at forecasting: Better skill after 3-4 months than “persistence”Skillful up to 9 months into future
Correlation Skill for NINO3 forecasts
NINO3 Predictions
ENSO Prediction “Plumes”
How to predict?
Forecasts courtesy of IRI (Lamont-Doherty)
How is forecasting possible?
The tropical ocean-atmosphere system is coupled.
Models are initialized with real observations
The system has persistence (“memory”)
