Class #16 Monday, October 4, 2010

Class #16: Monday, October 4

Chapter 8 Oceanography and

El Niño/La Niña/ENSO

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Sea Surface Temperatures

• Are highest in the tropics, lowest at the poles.

• In middle latitudes and subtropics, are higher on east coasts than west coasts.

• In polar regions, lowest temperatures on east coasts.

• In tropical regions, highest temperatures on west coasts.

• Are highest in the equatorial western Pacific in the “warm pool” and the Indian Ocean.

• Correspond to warm and cold surface ocean currents.

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Major Ocean Currents

Fig. 8-7, p. 214

Fig. 8-8, p. 215

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Surface pressure, surface wind, and ocean currents

• The subtropical highs are persistent enough to create persistent anti-cyclonic wind flow.

• These winds create gyres of anti-cyclonic ocean surface currents.

• Ocean currents are bounded by land.

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Wind and ocean current direction

• Friction between the air and the sea surface forces the water to move.

• The Coriolis force turns the water to the right (NH) or left (SH).

• Moving water influences the layer of water beneath.

• The entire pattern is called the Ekman spiral.

• On average, water moves to right (NH) or left (SH) in Ekman transport.

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Cold currents, west coast, and upwelling

• Ekman transport moves water away from the shore, but that water must be replaced.

• Replacement water rises from below the thermocline. Mixing and cold water brings nutrients close to the surface and favors sea life.

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El Niño

• Named “The (boy) child” for the season of most common occurrence.

• Is a common but short-lived feature, but occasional episodes last for months or a year or more. The episodes are what we call El Niño today.

• El Niño is a phenomenon that affects the entire Pacific Ocean and weather around the globe.

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Characteristics of El Niño

• Abnormal warming of the waters off Ecuador and Peru.

• Upwelling ceases

• Warm waters come from the western Pacific

• Trade winds weaken

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La Niña

• Generally, opposite conditions to El Niño

• Also described as an enhancement of normal conditions

• Abnormal cooling of ocean waters in the eastern Pacific

• Upwelling is enhanced

• Trade winds are stronger

How to get the latest information about El Niño

• Google on “ENSO diagnostic discussion”

• Choose the first entry, the National Climate Prediction Center

• Look at the latest discussion and the weekly update

• ENSO is “El Niño Southern Oscillation”

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Current phase of ENSO: La Niña

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Watching the change from El Niño to La Niña

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The heat content of the upper ocean changing with La Niña

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Temperature anomalies extend below the surface

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Outgoing longwave radiation is positive for clear skies

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La Niña is forecast to continue through the winter of 2010-11

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Sea level/Eastern Pacific rises in El Niño, sinks in La Niña

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El Niño (red) and La Niña (blue) have irregular cycles of 2-7 years.

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ENSO is the acronym for El Niño Southern Oscillation

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North Atlantic Oscillation (NAO), positive phase, period ~ 10 years