ENSO

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ENSO

• El Nino
• Southern Oscillation
• La Nina

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El Niño Media Hype?

• There is nothing weird about El Nino.
• Many factors affect weather events.
• Weather extremes big story
• El Nino is trendy catch phrase.
• Desire for a sound bite.

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Not the only cycle!! Factors for Long-range
Forecasting

• El Nino/Southern Oscillation
• Pacific Decadal Oscillation
• Quasi-Biennial Oscillation
• The Solar Cycle
• North Atlantic Oscillation

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What is El Nino?

• A disruption of the average oceanic-atmospheric
  system in tropical Pacific Ocean.
• El Nino means The Child (Christ Child)

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What happens in El Nino?

• Trade winds relax or reverse.
• Warmer eastern Pacific and cooler western
  Pacific.
• Less upwelling along S. America coast.
• Changes distribution of pressure centers
  Southern Oscillation.
• El Nino The Child commonly occurs around
  Christmas.
• Opposite is La Nina

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Normal situation
Normal situation
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When the trade winds blow, warm Pacific water is
pushed west, piling up near Australia and
Indonesia.
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El Nino situation
El Nino situation
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Trade winds break down and blow from west to
east, winds drive the warm water eastward,
spreading out across the Pacific and up against
South America.
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Normal Pressure and wind
Normal P and wind
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Southern Oscillation
Southern Oscillation
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ENSO

• El Nino / Southern Oscillation
• EN/SO

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Effect on Winter in NA

• Jet stream over N. America splits into two forks.
• Southern fork produces wetter weather over
  southern U.S.
• Northern fork keeps colder air in Canada so
  midwest has milder winter.

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Warm equatorial waters increase the temperature
contrast between the equator and the poles,
strengthening the jet stream!
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When Pacific waters are cool, the temperature
contrast is less and the jet stream weakens and
drifts north.
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Effect on Summer in NA

• Tends to hamper development of Atlantic Ocean
  hurricanes.
• Slight tendency for drier conditions in Ohio
  Valley and Mid-Atlantic States.
• La Nina
• Increase in wild fires in Florida all year

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Effect on Daily weather in NA

• Most strongly felt in S. California strong
  winter storms southern shift of storms
• Otherwise - Not much!

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Global Effects of El Nino

• Closer to tropical Pacific stronger the
  influence
• More rain and storm activity in Eastern Pacific
  (S. America)
• Drier in Western Pacific (Asutralia and
  Indonesia)
• Less intense Atlantic hurricane season.
• Strongest effect felt in each hemisphere during
  winter

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Discussion ??