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Describe the general atmospheric and oceanic circulation patterns that characterize La Nina and El Nino Describe the effects of La Nina and El Nino Explain.

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Presentation on theme: "Describe the general atmospheric and oceanic circulation patterns that characterize La Nina and El Nino Describe the effects of La Nina and El Nino Explain."— Presentation transcript:

1 Describe the general atmospheric and oceanic circulation patterns that characterize La Nina and El Nino Describe the effects of La Nina and El Nino Explain some of the related ecological effects of El Nino Explain coral bleaching and how it relates to El Nino and La Nina Explain how hurricanes are impacted by El Nino/La Nina Explain how we know that ENSO is natural Describe the relationship between ENSO and global warming Describe the current ENSO conditions

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4 The Southern Oscillation Naturally occurring cyclical change in Pacific ocean and wind circulation patterns Paleorecord indicates it has been occurring for 50 million years ago Has global teleconnections Occurs every 2-7 years, a temporal scale larger than seasons Global warming does not cause El Nino, but there may be interactions between the two. Two endpoints of oscillation, La Nina and El Nino Also referred to as ENSO

5 The Southern Oscillation

6 Walker circulation: normal or average conditions West Pacific –Warm ocean water –Low pressure –Unstable atmospheric conditions East Pacific –Cold water upwelling –High pressure –Stable atmospheric conditions

7 El Nino Tradewinds slow and reverse direction Eastern Pacific –Upwelling ceases –Warmer surface water –STHP weakens –Wet and unstable conditions Western Pacific –Cooler surface water –Low pressure weakens –Drier and stable conditions

8 El Nino Drawing/animation

9 El Nino: Flooding and mudslides in California and South American coast

10 El Nino: Drought and fire in western Pacific

11 El Nino: Loss of cold water upwelling and diminished phyoplankton blooms in E. Pacific Animation

12 Phytoplankton: primary producers Serve as food for zooplankton and higher trophic levels Diatoms Cyanobacteria Dinoflagellates Coccolithophorids

13 El Nino: Collapse of fisheries along South American coasts due to loss of cold water upwelling

14 Increased rainfall and vegetation cover in arid regions of western US

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16 El Nino: Hanta virus outbreaks in Western US http://www.cdc.gov/ncidod/diseases/hanta/hps/noframes/elnino.htm

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18 La Nina Amplification of normal Walker circulation –Easterly tradewinds grow stronger (E to W) –More warm water piles up in western Pacific –Lower pressure, more wet and unstable in western Pacific –STHP in eastern Pacific grows stronger, cooler and drier conditions –Greater upwelling Drawing

19 La Nina Drawing

20 Hurricanes and the Southern Oscillation Hurricane tracks for La Nina (left) and El Nino years (right) 1950-2001

21 Hurricanes and the Southern Oscillation Fewer hurricanes in Atlantic/Caribbean with El Nino –Reversal of tradewinds and strong more southerly subtropical jet weaken hurricanes through increased wind shear More hurricanes in Atlantic/Caribbean with La Nina –Tradewinds blowing from east to west favor hurricane development. –Subtropical jet stream further north

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23 bleaching

24 Coral bleaching and the Southern Oscillation Caused by prolonged high sea surface temperatures. At high temps: –Zooxanthellae (photosynthetic algae) in coral decrease production of photosynthate for coral animal These changes result in the expulsion of zooxanthellae from coral polyps Corals deprived of color and food, decline and death

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26 El Nino brings coral bleaching to central-eastern Pacific and Caribbean. La Nina brings bleaching events to Australia and the western Pacific

27 ENSO and global warming models ENSO not caused by global warming ENSO is natural cycle but influenced by global warming More El Nino conditions under global warming? Greatest variability in ENSO over past century than the preceding 7000 years

28 Normal ENSO fluctuations during Eocene (50 mya)

29 Normal ENSO fluctuations during Eocene warm period (50 mya)

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31 Current Southern Oscillation conditions Synopsis: The chance of El Niño is at 60-65% during the Northern Hemisphere fall and winter. http://www.cpc.ncep.noaa.gov/products/analysis_monitor ing/enso_advisory/ensodisc.pdf

32 Other ENSO states and oscillations Modokai El Nino North Atlantic Oscillation Arctic Oscillation Pacific Decadal Oscillation


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