El Niño (Week 7)
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This 4 page Class Notes was uploaded by Erica on Monday October 26, 2015. The Class Notes belongs to BIOEE 1540 at Cornell University taught by Bruce C. Monger in Fall 2015. Since its upload, it has received 30 views.
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Date Created: 10/26/15
El Ni o and Other Climate Oscillations 1 Historical Perspective EI Niin The roughly periodic warming of coastal waters off of Peru and Ecuador lasts 8 months Peruvian sailors named the term The Childquot Warm southward current occurred annually but occasionally seemed more intense 0 Only the extreme events are now considered El Ni o every 3 to 7 years Southern Oscillation Southern Oscillation the periodic reversal of the Walker Circulation Cell 1920 Sir Gilbert Walker noticed correlations between Australia amp Tahiti regarding atmospheric pressure Idealized Hadley Circulation 0 Winds at the ocean surface I Rush toward the equator I Coriolis force turns the winds east 9 west 0 Wind Aloft I Rush away from the equator I Coriolis force turns winds west 9 east 0 Idealized vs Actual Pattern I Differences because of unequal heating of land amp ocean I Land heats more strongly than ocean in summer amp cools more strongly than ocean in winter differences in heat of rock seawater o WalkerCirculation I East West atmospheric circulation cell I Winds at ocean surface I Winds aloft I Walker discovered that this circulation cell periodically reverses direction 0 Under Normal conditions trade winds in the Pacific move East 9 West I Winds pile up warm surface water creating thick pool of warm water the warm poolquot I Piled up water tilts the thermocline deeper in west amp shallower in the east Low SLP High SLP High SLP Low SLP quot Wm w Orran 3 tuuwnh 39Fquotquot393quotquot 39l gNormal Conditions ENSO El Nifio Southern Oscillation o Coupled oceanatmospheric interactions I Roughly periodic occurrence of prolonged warming of coastal waters off of Peru and Ecuador I Coherent change in the eastwest atmospheric circulation cell over the Pacific 9 results in coherent changes in atmospheric pressure patterns precipitation patterns and wind direction I Index A simple index number is used to describe El Ni o conditions 0 El Ni o can be observed by moored buoys with weather instruments on top of them Sea Surface Temperature Patterns 0 La Nina Strong trade winds equatorial upwelling and cooling in the Eastern Pacific 0 Normal Normal trade winds upwelling and cooling in the Eastern Pacific 0 El Nino Weak or reversed trade winds little no equatorial upwelling and strong warming in the Eastern Pacific 2 Direct Indirect Impacts of El Ni o Direct Impacts 0 Pacific Precipitation amp Storm Patterns I Relative cooling in Western Tropical Pacific creates drought conditions in Australia Indonesia I Relative warming in the Central amp Eastern Tropical Pacific creates heat energy for formation of intense precipitation and storms I Low equatorial productivity I Pacific hurricanes increase but Atlantic hurricanes decrease during El Ni o I Effects biological productivity Teleconnections Indirect Impacts 0 Changes in global climate 0 Changes in the jet stream I In uences prevailing wind direction at a given location o ENSO produces such a disturbance that can then propagate around the world Direct Impacts o 2015 El Ni o event 0 All models predict El Ni o to continue into the Northern Hemisphere winter 20152016 with many multimodel averages predicting a strong event at its peak strength Global Temperature Anomalies 0 El Ni o temporarily warms the planet La Ni a temporarily cools the planet 0 2015 El Ni o will create the highest global average temperature recorded in human history 0 3 Other Natural Climate Oscillations El Nino Southern Oscillation ENSO North Atlantic Oscillation NAO Atlantic MultiDecadal Oscillation AMO Pacific Decadal Oscillation PDO Arctic Oscillation AO OOOOO But in all cases they are superimposed on the trend of humancaused global warming 0 HumanCaused global warming is a MultiDecadal Trend