4.9: El Niño and La Niña

Thermohaline circulation

• drives the mixing of surface water and deep water

  • moves heats and nutrients all around the globe

  • driven by surface waters with unusually high amounts of salt

Review of wind patterns

• Trade winds (Hadley cells)

• Westerlies (Ferrell cells)

• Polar easterlies (Polar cells)

Tropical Storms

• Trade winds (contributed by Hadley Cells) sometimes cause disturbances when they blow over very warm ocean waters 

  • Air warms → forms isolated low-pressure area 

  • Coriolis effect results in this air circulating (either clockwise or counter)

  • Low pressure system continues to move over warm water and accumulates water vapor, strength, and speed.

• cyclones spin in opposite directions of hurricanes (happens in the south)

  • clockwise in south cause counter clock wise gyre

  • clounter clockwise in the north cause clockwise gyre

Gyre

A large-scale pattern of water circulation that moves clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.

• driven by trade winds and westerlies💨, Temperature, Gravity, Coriolis effect, Continents

• move warm and cold water around the world

• redistribute heat🥵 and nutrients

Upwelling

The upward movement of ocean water toward the surface as a result of diverging currents.

• Brings nutrients up that support the producers, which in turn support large populations of fish.  

Normal Year

• Surface water moves east to west

• Upwelling brings nutrients, producers, and fish to tropical west coast of South America

• Warm, moist air heads towards Indonesia

  • gyre and trade winds are pushing currents towards Australia and asia

  • give space for warm water to come up👏🐠

El Niño–Southern Oscillation (ENSO)

A reversal of wind and water currents in the South Pacific.

• Trade winds weaken

• Surface currents reverse

• Prevents upwelling

  • fish are sad 😔🐟

• Water warms

  

  • More rain in Peru, U.S. southwest & south

  • Fewer Atlantic hurricanes

  • Dry & hot in Australia, Africa, S.E. Asia

  • Milder winter in N.E. United States

La Niña

• “Reverse of El Nino”

• Coriolis effect contributes to conditions

  • Air moves towards equator replacing rising hot air → moves surface water → upwelling

• Cooler than average surface temperatures off the tropical west coast of South America

  • we have drier weather🏜

  • Australia gets more rain🌧