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. 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 Tropical cyclone destruction: 4 reasons? Which side has the most intense destruction? Trends and variability in tropical cyclone activity

Tropical Climate

Video: Chasing El Nino

The TAO buoy array

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

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

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

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

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

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)

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

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

Disastrous effects of 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 devastated5.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, malnutritiondisease

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

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

Extratropical Climate

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

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

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

Arctic Oscillation Index

Arctic Oscillation Index: Prediction

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

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