PowerPoint PresentationSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Unit VI. Coupled SystemsEl Niño and the Southern Oscillation (ENSO)Coupled SystemSOI (Southern Oscillation Index)Walker CirculationB. Walker CirculationCharacteristics of the “normal” condition:• Strong easterly trades• Concentration of warm water in W Pacific• Surface water in W Pacific thick• Sea level in the W Pacific is high• Atmospheric pressure over Australasia is low (rainy); over Tahiti it is high (dry).Characteristics of the “normal” condition:• Off Peru, off shore winds produce coastal upwelling, productive fisheries.• Atmosphere over S America around Peru, high pressure, dry.Easterly trades off the coast of Peru weaken around Christmas time.Fishermen traditionally call this time of year “El Niño”.In some years, the winds weaken, upwelling ceases, but does not come back for a year or more. This is what we now call El Niño.The Warm Pool, sloshes back across the Pacific.Kelvin Wave: Corilois Effect keeps the wave intact across the Pacific Ocean, until it hits the west coast of South America.How does El Niño influence weather?Direct (within the tropical Pacific region)Indirect (global, outside the tropical Pacific)El Niño, La Niña and “normal”…..Consequences of El Niño: (Direct)•••••Rain in PeruCollapse of Peruvian fisheriesDrought in Australia/IndonesiaWeakened Asian MonsoonRain in TahitiConsequences of El Niño: (Indirect)Through the ocean…..Warm Kelvin Wave diverted N and S when impacts South America.Sends anomalously warm water along the coast of western US and southern S. America.Water mass changes influence atmospheric jet stream…. Rainfall = transfer of energy through release of latent heat.ENSO through time: Does the frequency and amplitude of ENSO remain constant? Might it change under a warming planet?Looking at ENSO past…….tropical coralsENSO through time:• ENSO is a pervasive feature of the climate system…. Present under many different climate states.• However, ENSO exhibits large variations in frequency and amplitude, much larger than during the historic record.• ENSO in a warmer world might be very different than