Atmosphere-Ocean Interactions: Major Ocean Currents, El Niño, and Upwelling, Study notes of Meteorology

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Chapter 11, Part 2

Atmosphere-Ocean Interactions

Major Ocean Currents

January Wind and Pressure

Comparison Wind & Ocean Currents

Comparison Wind & Ocean Currents

Influence of Wind on Ocean Currents

• Wind blowing over the oceans causes the

surface water to drift along with it.

• Ocean currents do not follow the wind

pattern exactly. They flow in semiclosed

circular whirls called gyres.

Upwelling

• Because the surface current on the west coast is directed out to sea, this causes an upwelling of cold water from below the surface.
• The upwelling is strongest at Cape Mendocino because the wind parallels the coast.

El Niño

• A similar upwelling usually occurs on the west coast of S. America, bring nutrient rich cold water to the surface.
• Near the end of the year (Dec/Jan) warm water moves south, stopping upwelling.
• Called El Niño (Spanish for boy child).

Major El Niño Event

• At irregular intervals of 2 to 7 years, the

warming covers a large area of the Pacific

Ocean.

• Fish and birds die because of the loss of

nutrients.

• Weather around the world is disrupted with

some areas receiving more rain than normal

and others less.

Non-El Niño Conditions

• Normally, trade winds blow toward the west (H to L).
• Surface water near the equator is cool in the east and warm in the west.
• The wind raises slightly the water in the western Pacific, producing a weak countercurrent.

El-Niño Conditions

• Air pressure rises over the western Pacific and falls over the eastern Pacific, weakening the trade winds and strenghtening countercurrent.
• Surface water warms over western Pacific and heads eastwards (Kelvin wave – only 15cm high).

Kelvin Wave

• Kelvin wave moving eastward in March/April 1997.
• White areas are 20cm (8 in.) higher than average.
• Red areas are 10cm (4 in.) higher than average.

Global Effects of El Niño

• Droughts in Indonesia, southern Africa, and

Australia.

• Heavy rains and flooding in Ecuador and Peru.
• Storms in California and heavy rain in Gulf

Coast States.

• A strong El Niña also effects weather globally.

Regions Effected by Strong ENSO

Dry

Wet

Warm

Winter Weather Patterns over

North America

El Niño La Niña

Summary

• Ocean currents flow in semiclosed circular

whirls and roughly follow the wind direction.

• Wind blowing parallel to the coast can lead to

upwelling of cold water from below.

• In an El Niño event water in the eastern

Pacific warms and water in the western Pacific

cools.