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What Are the El Nino and La Nina?

What Are the El Nino and La Nina?. Review of last lecture. Tropical cyclone genesis: Western Pacific has the highest averaged number per year. 6 necessary conditions. 4 stages.

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What Are the El Nino and La Nina?

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  1. What Are the El Nino and La Nina?

  2. Review of last lecture • Tropical cyclone genesis: Western Pacific has the highest averaged number per year. 6 necessary conditions. 4 stages. • Tropical cyclone structure: 3 major components, rotation direction of inflow and outflow, location of maximum wind and rainfall, 3 feedbacks • Tropical cyclone intensity scale. Category 1: 74mph, category 5: 155mph • Hurricane names: alphabetically, 6 lists in rotation • Trends and variability in tropical cyclone activity • Tropical cyclone destruction: 4 reasons? Which side has the most intense destruction? • Tropical cyclone forecast: track and intensity Currently which skill is better?

  3. Tropical Climate

  4. The TAO buoy array

  5. Tropical mean state: Sea surface temperature (SST) Indo-Pacific warm pool Eastern Pacific cold tongue 2 basic regions

  6. Tropical mean state: Precipitation Inter-tropical convergence zone (ITCZ) Strong rainfall (heating) Weak rainfall GPCP Annual Mean Precipitation for 1979-2005 (mm/day)

  7. Tropical mean State: Walker Circulation • An atmospheric circulation cell oriented along the equator with rising motion in the west and sinking motion in the east, which is induced by the SST contrast between the Indo-Pacific warm pool and eastern Pacific cold tongue

  8. is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water towards the ocean surface, replacing the warmer, usually nutrient-depleted surface water. Ocean upwelling • Equatorial upwelling: Due to Coriolis effect • Coastal upwelling: Due to Coriolis effect

  9. Tropical mean State: Ocean-atmosphere feedback • Interacts with underlying Pacific Ocean with stronger upwelling (cooling) in the east, leading to a positive feedback.

  10. El Nino/Southern Oscillation (ENSO): The 4-year oscillation • El Nino: Very warm sea surface temperature over central and eastern tropical Pacific, which occurs every 3-7 years. The Walker Circulation becomes disrupted during El Niño events, which weakens upwelling in eastern Pacific. • La Nina: the opposite condition to El Nino • Southern Oscillation: The atmospheric oscillation associated with the El Nino-La Nina cycle. • The whole phenomena is now called El Nino/Southern Oscillation (ENSO)

  11. Typical ENSO period is 3-7 years, but with significant irregularity

  12. The 1997-1998 El Nino event

  13. The dramatic impacts of ENSO around the globe Flood in Lakeport, California as a result of the 1998 El Nino event Bushfire in Australia as a result of the 1998 El Nino event

  14. Disastrous effects of 1982-1983 El Nino: 1.Australia-Drought and devastating brush fires 2.Indonesia, Philippines-Crops fail, starvation follows 3.India, Sri Lanka-Drought,fresh water shortages 4.Tahiti-6 tropical cyclones 5.South America-Fish industry devastated - decrease in nutrients off Peru- fewer fish (anchovy) 6.Across the Pacific-Coral reefs die 7.Colorado River basin-Flooding, mud slides 8.Gulf states-Downpours cause death, property damage 9.Peru, Ecuador-Floods, landslides 10.Southern Africa-Drought, disease, malnutrition

  15. Movie time! Chasing El Nino

  16. Land-sea Contrast: Seasonal “Monsoon” Seasonal temperature distributions: • T over land > water in summer • T over land < water in winter

  17. The Seasonal “Monsoon” • A seasonal reversal of wind due to seasonal thermal differences between landmasses and large water bodies • Orographic lifting often enhances precipitation totals

  18. Extratropical Climate

  19. Mean State • Westerly winds and jet streams • A constant Polar Vortex: transport/mixing, important for ozone hole

  20. The Pacific/North American Oscillation (PNA): The way El Nino/La Nina affect U.S.

  21. The Strengthening/Weakening of Polar Vortex • North Pole: Arctic Oscillation (AO) • South Pole: Antarctic Oscillation (AAO)

  22. Tropical-extratropical Interaction • Zonal mean (3 cells) • ENSO • The interactions are mutual

  23. Summary Tropical climate: • Mean state: The two basic regions of SST? Which region has stronger rainfall? What is the Walker circulation? • Mean state: Two types of ocean upwelling, ocean-atmosphere feedback • El Nino and La Nina: Which region has warm SST anomaly during El Nino? 4-year period. • Land-sea contrasts: seasonal monsoon Extratropical climate: • Mean state: westerly winds, polar vortex • What is the primary way El Nino affect extratropics? (PNA) • The oscillations associated with strengthening/weakening of polar vortex: AO, AAO

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