El Niño Southern Oscillation (ENSO)

• El Nino Southern Oscillation (______): coupled atmosphere-oceanic system

  • A change in one results in a ______ in the other and vice versa

  • "______ _______" refers to the ocean component

  • "______ ______" refers to the atmospheric component

  • This connection was discovered in the late ______'s, and La Nina and Neutral ("normal") conditions were recognized in the _____'s

ENSO; change; El Nino; Southern Oscillation; 1960; 1980

• Revisiting Atmospheric Circulation

  • The ______ _______ operates between 0 - 30 degrees latitude in both hemispheres

  • At the equator (0 degrees latitude) the Coriolis Effect is _____

    • This is why we don't see tropical cyclones originate until about ____ degrees latitude

Hadley Cell; zero; 5

• ______ _____: secondary convection cell that operates within the Hadley Cell over the equatorial Pacific

  • Only present within about ____ degrees of the equator, where the Coriolis effect is absent or minimal

  • Powered by _______ surface waters

  • _______ convection cell

    • Polar, Ferrel, and Hadley cells are north-south convection cells

Walker Cell; 5; ocean; East-west

• Revisiting Sea Surface Temperature

  • Upwelling along the _____ coasts of North and South America bring _____ ocean water to the surface

  • As winds blow across the equatorial Pacific in the Walker cell, they _____ ____, eventually rising in the ______ Pacific

west; cooler; warm up; western

• Sea Surface Temperature

  • When there is a ____ temperature difference between the _____ waters in the ______ Pacific and the ______ waters in the ______ Pacific, strong westward-blowing winds push water toward the _____ Pacific

high; cooler; eastern; warmer; western; western

• Walker Circulation

  • Sea level is _____ in the western Pacific

  • Pushing water westward creates a ____ that is filled by the ______ of deep water in the _____

  • Deeper waters contain nutrients that _____ phytoplankton growth; these photosynthetic organisms form the _____ of the oceanic food web, thus encouraging _____ fish populations

higher; void; upwelling; east; promote; base; large

• Where Temperature Anomalies Most Pronounced

  • Scientists pay close attention to the temperature anomalies that form in the "______" region to determine changes in Walker Circulation

  • The Nino Region 3.4 extends from _______ degrees west and ____ degrees N - 5 degrees S

  • Deviations from "_____" conditions are distinguished by a sustained deviation of  _____ degrees C

  • When there are _____ consecutive ____-month running mean of sea surface temperatures in the Nino 3.4 region +0.5 degrees C, ____ ______ conditions are met

  • When there are five consecutive 3-month running mean of sea surface temperatures in the Nino 3.4 region - 0.5 degrees C, ___ _____ conditions are met

Nino 3.4; 120-150; 5; neutral; 0.5; five; 3; El Nino; La Nina

• El Nino and La Nina

  • The Walker Cell depends on _____ ______ ______ differences between the eastern and western Pacific regions

  • These differences can be most pronounced in ______

  • Peruvian fisherman noticed that when ______ is reduced or stops completely, their catches diminish

  • El Nino was named because it is coincident with the ______ holiday

    • El Nino refers to the birth of Jesus Christ, which is celebrated every December

  • La Nina is the corresponding ____ phase

sea surface temperature; December; upwelling; Christmas; cold

• Neutral Conditions

  • ______ _______ blow east to west, resulting in an average 8 degrees C (14 degrees F) difference between the eastern Pacific and western Pacific sea surface temperatures

  • Water is pushed _____, cold water _____ off the coast of South America to fill the gap

  • The average sea level height is 46 cm (1.5 ft) higher in the _____ Pacific than in the ______ Pacific

  • The thermocline is about _____ m (450 ft) deep in the western Pacific

  • The thermocline is about _____ m (90 ft) deep in the eastern Pacific

Trade winds; westward; upwells; western; eastern; 150; 30

• La Nina

  • An amplification of ______ conditions. The trade winds blow _____

  • _____ water is pushed to the western Pacific, resulting in ______ upwelling in the eastern Pacific and ______ sea surface temperatures

  • The neutral rainfall pattern shifts farther _____ than normal

neutral; stronger; More; stronger; cooler; west

• El Nino

  • When the trade winds _______ (or reverse), the normal flow of water away from South America ______

  • Ocean water ______ _____ off South America, pushes down (_______) the thermocline, and results in ______ upwelling

  • The sea surface temperature _______ to greater than normal in the eastern Pacific

  • The western Pacific becomes ____ and rainfall ______ in the central Pacific

weaken; decreases; piles up; thickens; decreased; increases; dry; increases

• Determining if it's El Nino or La Nina

  • El Nino and La Nina happen when ______ the oceanic and atmospheric conditions present

  • If it's just warmer sea surface temperature but no impacts to the Walker Cell, then it's not El Nino

both

• How Long These Events Last

  • El Nino and La Nina typically last for _______ months

  • The longest El Nino lasted for _____ months and the longest La Nina lasted _____ months

  • El Nino events typically last for _____ than a year, while La Nina events can commonly persist for _____ years

  • They tend to develop in the ____ (March-June), reach peak intensity during the late ________ (November-February), and weaken during the following ______/early summer

  • El Nino is typically, but not always, followed by La Nina, especially if the El Nino was strong

  • The ________ between the two states (warm/cold) is what gives the El Nino/La Nina the collective term El Nino Southern Oscillation (ENSO)

9-12; 18; 33; less; two; spring; autumn/winter; spring; oscillation

• Current Conditions: El Nino Advisory

  • Environmental monitoring allows scientists to forecast the development of El Nino and La Nina events up to about ____ _____ in advance

  • As of September 30, 2026, "El Nino is _____, with a greater than 90% chance of a very strong event during the ______ Hemisphere fall and winter 2026-27"

a year; strengthening; Northern

• Impacts of This Year's El Nino

  • _____

    • The United Nations World Food Programme "estimates this latest El Nino could push ____ million people into acute hunger."

      • Latin America and the Caribbean, as well as large parts of Africa, Asia, and the Pacific, could experience the biggest impacts

    • Callahan and Mankin (2023) explores the impact of El Nino on global economic growth: "El Nino events persistently ______ economic growth."

  • ______-Related Deaths

    • The University of Chicago Climate Impact Lab projects that "_______ lives will be lost [between September 2026 and February 2027] due to heat in the first half of this El Nino, compared to a normal year."

Hunger; 49; decrease; Heat; 451,000