EVSC10001 Lecture Notes - Lecture 17: Upwelling, Thermocline
10 Jun 2018
School
Department
Course
Professor
What is El Nino?
Warming of equatorial eastern Pacific Ocean
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Occurs about once every 2-7 years
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Affects coast of S. America at Christmas
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Upwelling is suppressed -> fish die because not enough nutrients -> collapse
of fisheries
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Normal conditions
STRONG SE trade winds -> cool at South America
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Low pressure over N. Australia (rainfall), high pressure in east Pacific
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El Nino conditions
SE trades weaken
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Equatorial pacific warms
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Warmer in S. America region
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High pressure over N. Australia (less rainfall)
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Low pressure in east Pacific
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Upwelling in eastern equatorial Pacific reduced -> warms ->
thermocline deeper
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Easterly winds weaken
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Heavy rainfall moves to central pacific (low pressure)
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What is La Nina?
Cooling of eastern equatorial pacific
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Enhanced normal
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Easterly winds strengthened
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Heavy rainfall + low pressure in west is enhanced
Cold in central
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Lots of floods in Australia
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What is southern oscillation?
Variation in rainfall + pressure
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El Nino - pressure higher in west + lower in east
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SOI: pressure diff b/w Tahiti and Darwin
El Nino - negative
More rainfall - lower P than normal
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High pressure in darwin
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La Nina - positive
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El Nino impact on weather
Dec-feb - Northern hemisphere winter
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June-Aug - influences weaker b/c sea surface temps arent as strong - drier in
australia
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EL nino on australia
Decile 1 = dry
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Decile 10 = 10 wettest
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Much of E. Australia in drier conditions
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La nina in australia
Much wetter in winter + spring
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Heaver rainfall in north
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2010-11 La Nina
Wettest on record june-feb
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Increased river, increased soil moisture -> more water on land
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Decrease in global sea level
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Decrease global mean temps
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2015-16 El nino
Warm sea surface temp across pacific
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Dry
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Not as coherent pattern
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Typically lasts 12 months
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Peak pressure Dec-Jan
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El nino = release of heat from ocean -> atmosphere
Less cold water in E. pacific
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Increase global mean temps
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SUMMARY:
El nino - pacific warms -> heaviest rainfall + lower pressure in central Pacific ->
reduced rainfall + higher pressure in W. pacific and Australia
About ever 3-7 years
La nina - E. pacific cools -> heavier rainfall + lower pressure over E. Australia
El-Nino Southern Oscillation
Wednesday, 6 June 2018
4:46 pm
