ENSO Prediction and Policy

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”)