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El Niño- Southern Oscillation ‘ENSO’

El Niño- Southern Oscillation ‘ENSO’. Unit 3 Lecture 9. El Niño- Southern Oscillation ENSO events Normal conditions ENSO conditions Cause of ENSO events. ENSO Events. Ocean/atmosphere interaction surface water temperature/ atmospheric pressure Occurs on a 3-4 year cycle

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El Niño- Southern Oscillation ‘ENSO’

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  1. El Niño- Southern Oscillation ‘ENSO’

  2. Unit 3 Lecture 9 • El Niño- Southern Oscillation • ENSO events • Normal conditions • ENSO conditions • Cause of ENSO events

  3. ENSO Events • Ocean/atmosphere interaction • surface water temperature/ atmospheric pressure • Occurs on a 3-4 year cycle • Earliest written records – 1500’s Spanish explorers • Phenomenon usually observed around Christmas • season in waters off Peru and Ecuador

  4. Warm surface temp → Low-pressure tropical cyclones (hurricanes or typhoons)

  5. Cause of ENSO Events - Normal Conditions Tradewinds • Tradewinds ‘push’ surface waters at western edge of basin • Warm water piles up in west “Pacific warm pool” , sea surface 1m higher • Pycnocline found at 100m depth at western edge of basin and only at • 30m depth at eastern edge of basin • Coastal winds ‘push’ waters offshore (i.e. via Ekman transport) • cold nutrient-rich waters subsurface waters upwelled

  6. Normal Conditions - Peru and Ecuador OCEAN • Cool, nutrient-rich coastal surface • waters • upwelled waters come from below • the pycnocline • Major fishery i.e. in the 1970’s 22% of all fish production came from coastal waters off of Peru and Ecuador NOAA

  7. Normal Conditions - Peru and Ecuador(cont’d) ATMOSPHERE • High pressure system over coastal Peru and Ecuador • dry in winter NOAA

  8. ENSO Conditions - Peru and Ecuador OCEAN • Warmer than normal, nutrient • deplete coastal surface waters • upwelled water comes from above pycnocline • Fishery crashes (lower catch, higher • prices at fish market) • causes death of organisms adapted to cooler, nutrient rich surface waters • upsets and shifts food web dynamics NOAA

  9. Cause of ENSO Events - ENSO Conditions Tradewinds Relax or Cease • Tradewinds no longer ‘push’ surface waters at western edge of basin • Pacific warm pool begins to flow back towards eastern edge of basin • via Equatorial Counter Current • starts to move in Sept., makes it to S. America in Dec. or Jan. • pycnocline flattens out • now found at a greater depth in the east • Coastal winds still ‘pushing’ waters offshore (i.e. via Ekman transport) • warm nutrient-deplete surface waters upwelled

  10. ENSO Conditions - Peru and Ecuador (cont’d) ATMOSPHERE • Low pressure system over coastal Peru and Ecuador • wet in winter • heavy rains cause flooding and landslides on usually dry land NOAA

  11. ENSO Conditions - Global • Flooding in North and South America (low pressure system) • landslides, erosion • Droughts in Australia (high pressure system) • fires • Switching position of pressure zones effects jet stream flow • increase in tropical storms in the Pacific • decrease in tropical storms in the Atlantic

  12. ENSO Conditions - Florida • More rain • Cooler • Increase in number and strength of • tornadoes • only two F4 tornadoes in FL occurred during strong El Niño years • Less hurricanes

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