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This 7 page Class Notes was uploaded by Sidnee Notetaker on Wednesday October 21, 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 18 views.
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Date Created: 10/21/15
E n no Tuesday October 20 2015 1206 PM I History of the Term El Ni o A The original definition of El Ni o goes back to 18th or 19th century when Peruvian sailors coined the term to describe a warm southward current that appeared annually near Christmas time off the Peruvian coast Hence the name El Ni o Spanish for quotThe Child quotChrist Childquot B The warm southward current occasionally every 3 to 7 years seemed much more intense than usual and eventually the term El Ni o came to refer primarily to these occasional extreme events C El Nino 1 The Roughly Periodic 37 years Occurrence of Prolonged ca 8 months Warming of Coastal Waters off of Peru and Ecuador D Southern Oscillation I i Equator t Callao 39 39 I F e 1 In the 1920 s Sir Gilbert Walker Analyzed Atmospheric Pressure Data Measured at Darwin Australia and Tahiti and Noticed Some Remarkable Correlations in the Two Data Sets E Why Are The Two Weather Stations So Well Correlated 1 The explanation if found by taking a closer look at the idealized Hadley Circulation 2 In particular the EastWest component of the tropical Hadley Cell F Recall The NorthSouth Component of the Hadley Circulation Subtropical 0 Polar J93 North Polo BO N 30 N Equator G 3D View of Idealized Hadley Circulation 1 Winds at the ocean surface a Rush toward the equator b Coriolis force turns the winds to blow from east to west 2 Winds Aloft a Rush away from the equator b Coriolis force turns the winds to blow from west to east H Recall the Idealized Versus Actual Pattern of Global Sea Level Pressure And Resulting Surface Winds El Nino Page 1 gUa EWWS Foam mun munowner mpgnoramdfsuhtml L39L39 1 Differences due to unequal heating of land and ocean 2 Land heats more strongly than adjacent ocean in summer and cools more than adjacent ocean in winter due to differences in specific heat of rock and seawater I WalkerCirculation EastWest Atmospheric Circulation Cell 1 Winds at the ocean surface move toward the equator but are deflected by Coriolis toward the right west to form surface trade winds 2 Winds aloft move away from the equator but are deflected by Coriolis toward the right east to complete the WalkerCirculation III Sir Gilbert Walker discovered that this eastwest atmospheric circulation cell periodically reverses direction J The Southern Oscillation 1 The Southern Oscillation is the Periodic Reversal of the Walker Circulation Cell Low SLP High SLP High SLP Low SLP h 39 1 1M l x v C to r r7 1quot HJXI w a K Southern Oscillation 1 The Coherent Change Periodic Reversal in the EastWest Circulation Cell Over the Pacific Walker Cell Resulting in Coherent Changes in Atmospheric Pressure Patterns Precipitation Patterns and Wind Direction Under Normal conditions in the Pacific the Trade Winds blow from east to west and in the process they do two things III The winds transport and pile up warm surface water on the western side of the Pacific to create a thick 200 meters pool of very warm ocean water called quotthe warm pool III The piled up water tilts the thermocline deeper in the west and shallower in the east The Southern Oscillation is the Periodic Reversal of the Walker Circulation Cell El Nino Page 2 Exceptionally Strorgg Normal Reversed quotquot1914 WE Trade Mnds Trade Winds 5 La Nina 5 Mme Ax Exceptionally Strong A b b m m m Trade Vl nds 39MM LI Iii Zn ans a There is a third state to the Southern Oscillation not shown in this figure associated with enhanced strength in the Trade Winds 2 El Nino Southern Oscillation ENSO Coupled OceanAtmospheric Interactions a In 1969 Jacob Bjerknes proposed that there was a physical connection between the oceanographic and atmospheric variations and now the oceanic El Nino and the atmospheric Southern Oscillation aspects are often combined in the single term 39EI Ni o Southern Oscillation39 ENSO that encompasses both the ocean and the atmosphere i Roughly periodic 37 years occurrence of prolonged ca 8 months warming of coastal waters off of Peru and Ecuador ii Coherent change in the eastwest atmospheric circulation cell over the Pacific Walker Cell resulting in coherent changes in atmospheric pressure patterns precipitation patterns and wind direction b Sea Surface Temperature Patterns During La Nina Normal and El Nino Conditions in the Pacific i La Nina Exceptionally Strong Trade Winds Equatorial Upwelling and Cooling in the Eastern Pacific ii Normal Normal Trade Winds Upwelling and Cooling in the Eastern Pacific iii El Nino Exceptionally Weak or Reversed Trade Winds Little or No Equatorial Upwelling and Strong Warming in the Eastern Pacific ENSO Index III A simple index ie a single number used to describe the severity of El Nino conditions ie the strength of the reversal in the Walker Circulation III Traditionally defined as the normalized difference in atmospheric pressure measured at Darwin Australia and Tahiti but more elaborate and robust metrics also exist ENSO Index U MULTIVARIATE ENSO INDEX quottulwi39lln quot1111 14 1 2 n O Standardized Departure NCAA quotEFRIquotPthsinl Science Dn mion 17mwruly of Colorado at BoulderfCIRES 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 htlp n39W JJ39 9er noaa gowpsd ensomei Red El Nino Conditions Blue La Nina Conditions c Warming of the surface water off of Peru during an El Nino Event is part of a El Nino Page 3 much greater warming event covering large parts of the eastern tropical Pacific and reaching down to the thermocline WW to 397 C T 4 r MI I IIMIIN 1 II int d El Nino s Progression 19971998 El Nino i March Westerly Wind Burst north of Australia ii April Kelvin Wave Reaches South America iii May Water Piles up off of South America iv June High SeaLevel Spreads North and South e What should happen to globalaverage temperature when the thick warm pool of water in the western Pacific spreads out across a large area of the equatorial Pacific during an El Nino period 0 The Correct Answer is a temperatures will go up as the area of warm water in contact with the atmosphere increases and allows the ocean to give up some of its stored heat to the atmosphere II Observing El Nino A Moored buoys with weather instruments on top of each buoy and an evenly spaced string of temperature and current meter instruments hanging below each buoy 3 00 I I I I II I I I I I II I I 350 TACITEIT DN Array I I I I II I I I l I I I I I II II I I I DIE a I I I I II II I I E quot I T I I II I I I I I I E E F E I39 E P E l 1058 I l l I I I I atlas f amps a L I H I u I T ubsltmfaolf u 39 39 I ll E lri 39E 16W LEW ISEIE39W 1th lE W l w EIIJ DW III Environmental Change Linked Directly and Indirectly to El Ni o A El Nino s Direct Impact on Pacific Precipitation and Storm Patterns 1 Relative Cooling in the Western Tropical Pacific Creates Drought Conditions in AustraliaIndonesia During an El Nino 2 Relative Warming in the Central and Eastern Tropical Pacific Heat Energy for Formation of Intense Precipitation and Storms Ex Draught and Fires in Indonesia Pacific Hurricanes Increase During an El Nino but Atlantic Hurricanes Decrease Flooding in the Western United States Normal Conditions El Nino Conditions gagizyv inal Low Equatorial Producrivity El Nino Page 4 Normal Conditions El Nino Conditions ig Equatorial Productivity Low Equatorial Productivity B Teleconnections Environmental Changes Linked Indirectly to El Ni o 1 The answer to how El Nino can influence weather patterns around to globe lies in what El Nino can do the Jet Streams that circle the globe Prevailing Wind Direction at a Given Location is Strongly Influenced by the Position of the Jet Stream 1 Jet streams have wavelike properties and just like a disturbance in water causes a wave to propagate outward so too does a regional disturbance in the jet stream position propagate in wavelike fashion around the globe ENSO produces such a disturbance that can then propagate around the world C The 2015 El Ni o Event 1 During June sea surface temperatures SST anomalies exceeded 10oC across the central and eastern equatorial Pacific Ocean 2 All models predict El Ni o to continue into the Northern Hemisphere winter 201516 with many multimodel averages predicting a strong event at its peak strength 3 Overall there is a greater than 90 chance that El Ni o will continue through Northern Hemisphere winter 201516 and around an 80 chance it will last into early spring 2016 D Global Temperature Anomalies Since the Industrial Era 1 El Nino temporarily warms the planet 2 La Nina temporarily cools the planet 3 If the 2015 El Nino is as big as many predict then global average temperatures will spike upward in 2015 4 Superimposing the 2015 El Nino warming onto the multidecadal trend warming will create the highest global average temperature ever recorded human history in 2015 El Nino Page 5 w El Nino global Laud ccau Icmpcmturc 2015 I Annual Menu 5year Running Mean Fl Nino no r I 11 330 1001 1030 10m 1060 1030 39 i0 lcmpumllll39c nuinul r 39i a quot W v r v 1 mn 1331 I 100439 1030 10 10 10mm 1080 Zr39x39ir l E Other Natural Climate Variations That Can Temporarily Warm and Cool the Earth 1 El Nino Southern Oscillation ENSO 2 North Atlantic Oscillation NAO 3 Atlantic MultiDecadal Oscillation AMO 4 Pacific Decadal Oscillation PDO 5 Arctic Oscillation AO But in All Cases they are Superimposed on a Very large MultiDecadal Trend that IS human caused global warming F North Atlantic Oscillation NAO Positive NAO Negative NAO Strong pressure difference Weak pressure difference between between lceland and Azores Iceland and Azores Stronger Westerly Winds Located Weaker Westerly Winds More Northward Located More Southward A39 Lalo I ll Pressure drops Frassurr lam I Jan 5 Dauluh G Pacific Decadal Oscillation PDO Positive Phase North Paci c cooler than normal Equatorial Paci c warmer than normal Negative Phase North Pacmc warmer than normal Equatorial Pacr c cooler than normal H Atlantic MultiDecadal Oscillation Derived from Global SST Data El Nino Page 6 03 AMO gt mean N Atlantic SS A 02 OJ I Time Variation of AMO o o r 39 0J 02 r 1860 1880 1900 1920 1940 1960 1980 2000 Spatial Coherence of AMo similar colors rise and fall in unison from year to year or decade to decade purple and red colors are out of phase years or decades of high temperatures for red means low temperatures for purple regions for the same year or decade I HumanCaused Global Warming is a MultiDecadal Trend 1 In All Cases The temporary warming and cooling effects of natural climate oscillations are superimposed on a very large multidecadal warming trend that represents humancaused global warming signal Global Land DCEan Temperature Index 39339 I Temperature anomaly DC C C3 ll 188i 119mm 19213 1940 1961 1980 2000 El Nino Page 7
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