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