El Niňo

What is El Nińo?

El Nińo: a disruption in the “normal” pattern in the Pacific Ocean.

Off the west coasts of continents, the Sea Surface Temperature is chilly. Fish love the cold water, especially anchovies.

During El Nińo, SST changes dramatically near Peru

The SST changes have really big consequences for the atmosphere.

This is the development of the most intense El Nińo ever recorded in 1997-98.

So, what happens during El Nińo?

The normal mean pressure features are these:

1. The Subtrop High moves south or weakens

2. Trade winds get weaker or reverse

3. The Aleutian Low strengthens

H

H

L

L

For January, 1998, this was the 1000 mb (surface)

Mean values Departures from the 30-year mean (Anomalies)

At 250 mb, there were changes caused by the surface pressure and temperature anomalies

Mean values Departures from the 30-year mean (Anomalies)

Look at the effect on the 250 mb wind (the Jet Stream!)

Mean values Departures from the 30-year mean (Anomalies)

The much stronger subtropical Jet Stream explains all the U.S. anomalies

La Niňa

This is the La Niňa event of 2006-07

This is the latest drought map.

The ENSO cycles vary in length and intensity ~ 6-18 months.There have been several big events in the last 20 years.

What is the current situation? El Nińo, La Nińa, or “neutral”?

Other circulation patterns and their effects

NAO: North Atlantic Oscillation

AO: Arctic Oscillation

PNA: Pacific/North American (oscillation)

PDO: Pacific Decadel Oscillation

The figures shown are from www.nc-climate.ncsu.edu/climate/patterns

NAO (North Atlantic Oscillation)

As the name tells us, this is a pattern located in the North Atlantic Ocean.

AO (Arctic Oscillation)

Here we are just interested in the Arctic.

From http://www.nc-climate.ncsu.edu/climate/patterns/NAO.html

PNA (Pacific North American Oscillation

PNA (Pacific North American Oscillation

PDO(Pacific Decadel Oscillation)

Warm Phase

Cold Phase

If both ENSO and the PDO are in the same phase, it is believed that El Niño/La Nina impacts may be magnified. Conversely, if ENSO and the PDO are out of phase, it has been proposed that they may offset one another, preventing "true" ENSO impacts from occurring (http://www.nc-climate.ncsu.edu/climate/patterns/PDO.html)

The current PDO index is +0.38 (http://jisao.washington.edu/pdo/PDO.latest)

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