Oceans & El Nino Ocean-atmosphere coupling matters

Key Points u Climate & ocean-atmosphere coupling –Seasonal heating stored in upper layers of ocean –Evaporation of water to atmosphere increases with temperature u The Ocean Circulation u El Niño, La Niña u Other Fluctuations

Evaporation u Increases with temperature

Schematic Layers in the Ocean Temperature 3700 m 100 m Mixed layer Deep ocean 0 m Horel and Geisler: Figure 4.5 u Deep water is cold and dense u Surface warmed by sunlight and mixed by wind

The Principal Links for Climate u Sea Surface Temperature 9/24/98 u Winds – Courtesy WGBH

Sea Surface Temperature u From Geostationary Satellite January, 1999

Key Points u Climate & ocean-atmosphere coupling u The Ocean Circulation –Ocean basins km deep –Filled with cold dense water from polar regions –Warmed from above in tropics and mid latitudes –Surface layers mixed by wind and seasonal cooling –Deep ocean overturns slowly ( ~ 2000 yr) u El Niño, La Niña u Other Fluctuations

Schematic Ocean Circulation Horel and Geisler: Figure 4.6 Ocean surface Ocean bottom Low latitudesHigh latitudes Mixed layer UpwellingDownwelling u residence time 2000 years

Conveyor Belt u A schematic view of the global ocean circulation Horel & Geissler after Broecker

Key Points u Climate & ocean-atmosphere coupling u The Ocean Circulation u El Niño, La Niña –Fluctuations every few years in equatorial Pacific –Feedback: ocean surface temperature ->atmospheric convection -> winds ->ocean currents -> temperature –Causes droughts and floods world wide u Other Fluctuations

Equatorial Pacific Sea SurfaceTemperature u El Nino u Normal u La Nina Dec 97 Dec 90 Dec 88 u NOAA/PMEL

El Nino Years

El Nino or La Nina? u El Nino : – Eastern and Central Pacific WARM – Indonesian rain area moves EAST – Coastal Andes: F Ocean: NO UPWELLING F Land: F LOODS u La Nina : – Eastern and Central Pacific COLD – Indonesian rain area NORMAL – Coastal Andes: F Ocean: UPWELLING F Land: VERY DRY

The El Nino Feedback u u Ocean-atmosphere coupling u u Slackening trade winds cause surge in upper ocean water along equator u u Ocean temperature anomalies persist for many months u u SST anomalies change atmospheric circulation and trade winds

Ocean Atmosphere - Normal – Courtesy NOOAA/PMEL

Ocean Atmosphere - El Nino – Courtesy NOOAA/PMEL

Associations of El Nino - 1

Associations of El Nino - 2

Consequences u Warm/cold winters u Floods u Droughts

Vegetation Stress u El Nino (top) u La Nina (bottom)

A TAO Buoy u Pacific Marine Environmental Laboratory

Current Status 10/11/00 u In between. Neither El Niño nor La Niña u TAO Array TAO Array

Current Status 2/13/00 u La Nina persists National Oceanic and Atmospheric Administration

A historical perspective u Sea Surface Temp- erature u Strength of trade winds PMEL

Key Points u Climate & ocean-atmosphere coupling u The Ocean Circulation u El Niño, La Niña u Other Fluctuations –Pacific Decadal Oscillation F Salmon catches, Alaska - California –North Atlantic Oscillation F Rainfall in Sahel F Drought in N.E. Brazil

Pacific Decadal Oscillation u Warm u u Cool Mantua et al

Selected Pacific Salmon Catches u Mantua et al Mantua et al u Black Warm PDO u Grey Cool PDO

Key Points u Climate & ocean-atmosphere coupling u The Ocean Circulation u El Niño, La Niña u Other Fluctuations

Sources of Information u Horel & Geisler Chapter 3, 4 u u ng_storm/day1.html u u PHC/Staff/hare/html/papers/pdo/PDO.html