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El Niño- Southern Oscillation ENSO. El Niño- Southern Oscillation 1.ENSO events 2.Normal conditions 3.ENSO conditions 4.Cause of ENSO events Unit 3 Lecture.

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Presentation on theme: "El Niño- Southern Oscillation ENSO. El Niño- Southern Oscillation 1.ENSO events 2.Normal conditions 3.ENSO conditions 4.Cause of ENSO events Unit 3 Lecture."— Presentation transcript:

1 El Niño- Southern Oscillation ENSO

2 El Niño- Southern Oscillation 1.ENSO events 2.Normal conditions 3.ENSO conditions 4.Cause of ENSO events Unit 3 Lecture 9

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

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5 Warm surface temp Low-pressure tropical cyclones (hurricanes or typhoons)

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8 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 Cause of ENSO Events - Normal Conditions

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

10 High pressure system over coastal Peru and Ecuador ~dry in winter Normal Conditions - Peru and Ecuador (contd) ATMOSPHERE NOAA

11 Warmer than normal, nutrient deplete coastal surface waters ~upwelled water comes from above pycnocline ENSO Conditions - Peru and Ecuador OCEAN 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

12 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 Cause of ENSO Events - ENSO Conditions

13 Low pressure system over coastal Peru and Ecuador ~wet in winter ~heavy rains cause flooding and landslides on usually dry land ENSO Conditions - Peru and Ecuador (contd) ATMOSPHERE NOAA

14 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 ENSO Conditions - Global

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

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