4The Southern Oscillation Index DarwinTahitiMean pressure is lower at Darwin than TahitiThe term “Southern Oscillation” was also coined by Gilbert WalkerThe SOI measures the strength of the Pacific Walker circulation
5The phenomenon is called SOUTHERN OSCILLATION… Thus, “EL NIÑO” is a condition in the central and eastern equatorial Pacific Ocean where unusual warming is occurring. (Note that the formation/development of El Niño is very far from the country.. )Then, why is it affecting the philippines..
6What is El Niño Warming of sea surface waters in the central and eastern tropical Pacific Ocean.El Niño: the ocean part: Warm phase of ENSO:El Niño - Southern OscillationSouthern Oscillation: the atmospheric part;a global wave patternLa Niña: is the cold phase of ENSO:Cool sea temperatures in tropical PacificEN events occur about every 3-7 years
8Initial results of diagnostic and statistical studies on general influences of ENSO on Philippine climateDuring El Niño EpisodeDuring La Niña Episode· Weak monsoon activityModerate to strong monsoon activity- delayed onset of the rainy season- early termination of the rainy season- increased cloudiness and widespread rains- occurrence of isolated heavy rainfall in short duration- near normal to early onset of the rainy seasonWeak tropical cyclones activityModerate to Strong tropical cyclones activity- tropical cyclones follow tracks further off the Philippines- near normal cyclone tracks (near and/or crossing the country)- less number of tropical cyclones entering the Philippine Area of Responsibility (PAR)- near-to-above normal cyclone occurrences in the PAR- rain-effective cyclonesBelow normal rainfallAbove normal rainfallAbove normal air temperaturesNear-to-below normal air temperaturesDrier weather conditionsWetter weather conditions
9Top: normal Bottom: El Niño condition Eastern boundaryShallow thermoclineCold, nutrient-rich waterMixing depth shallower than critical depthHigh NPPDeep thermoclineWarm, nutrient-poor waterMixing depth not as much shallower than critical depthLower NPPNormalEl NinoOpen University, 1998
10El NiñoLa NiñaEquatorial upwellingMuch weakerMuch strongerCalifornia Current upwellingWeakerStrongerCalifornia Current temperatureWarmerCoolerCalifornia Current thermoclineDeeperShallowerWest Pacific warm poolSpreads east across equatorCompressed in western Pacific
11Central America /Mexico RegionPeriodImpactIndonesiaLife of eventDrierNortheast BrazilMarch-MayCentral America /MexicoMay-OctoberWest CoastSouth AmericaWetterCentral South AmericaJune-DecemberSoutheast AfricaDecember-February
13Rainfall in thunderstorms and organized convection gives rise to latent heat release in the atmosphere, which determines atmospheric heating patterns.The heating patterns set up low level convergence and upper level divergence that drives Rossby waves in the atmosphere.These propagate to other regions (teleconnections) and determine the atmospheric circulation locally.
14Different flavors of El Niño Events come in different “flavors”El Niño refers to a warming of the tropical Pacific but this doesnot take account of surrounding areas and character of event.Tropical winds and rainfallrespond to total SSTs andso depend on time of yearand details. Surface windconvergence is in vicinityof warmest water, notanomaly.Small changes in SST canchange region of warmestwater by 1000 km or more!
15El Niño and Global warming 1998 warmest year on record, 2001 second warmestEl Niño contributes to global warmingThere is a pattern of more and bigger El Niños in past 20 yearsEl Niño yearsLa Niña yearsIs global warming contributing to changes in El Niño?Likely, yes, to some extent.Which part is natural variability?
17How will El Niño events change with global warming? El Niño involves a build up and depletion of heat as well as major redistribution of heat in the ocean and the atmosphere during the course of events.Because GHGs trap heat, they interfere.Possibly expand the Pacific Warm Pool.Enhance rate of recharge of heat losses.More warming at surface: enhanced thermocline enhanced swingsMore frequent El Niños?Some models more El Niño-like with increased GHGs.But models do not simulate El Niño wellNor do they agreeThe hydrological cycle is expected to speed up with increased GHGs. Increased evaporation enhances the moisture content of the atmosphere which makes more moisture available for rainfall. ENSO-related droughts are apt to be more severe and last longer, while floods are likely to be enhanced.
18Main effects of climate oscillations on pelagic species Changes in temperature/nutrients affect primary production and food webHigher trophic levels affected by changes in food availabilityChanges in temperature affect rates of growth/survivalFish/nekton with limited temperature range can move to water of preferred temperature, leading to range shifts
20Central Case: Rising Temperatures and Seas May Take the Maldives Under 80% of this island nation’s land is <1 m above water.Globally warming temperatures are causing sea levels to rise worldwide, endangering many island nations.The 2004 tsunami (tidal wave) hit the Maldives hard.