1. What Are the El Nino and La Nina?

2. Review of last lecture
The developmental stages and vertical structure of middle latitude cyclones (boundary between northern cold air and southern warm air, upper level low to the west of surface low)
How upper level longwaves and shortwaves may enhance cyclonic development at the surface (upper level low to the west of surface low)
The three regions of cyclogenesis and typical tracks
Lake effect
Anticyclones, heat waves and droughts
Climate change: move the tracks of the midlatitude cyclones towards the poles

3. The Tropical Atmosphere Ocean (TAO) buoy array by NOAA

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

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

6. 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

7. Ocean upwelling
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.
Equatorial upwelling: Due to Coriolis effect
Coastal upwelling: Due to Coriolis effect

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

9. Video: Chasing El Nino https://www.youtube.com/watch?v=TYR3GcSLHco

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

16. 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

17. World’s major monsoon systems
From Jay Fein 1987

18. Seasonal variation of monsoon rainfall

19. Impacts of monsoons: (1) Normal year
Dry season
Wet season

20. Impacts of monsoons: (2) Failure of monsoon and droughts
Drought affected area in Karnataka, India, 2012, image from Wikipedia

21. Impacts of monsoons: (3) Excessive monsoon and floods
Image from Doctors without Borders

22. Summary
Mean state: The two basic regions of SST? Which region has stronger rainfall? What is the Walker circulation?
El Nino and La Nina: Which region has warm SST anomaly during El Nino? 4-year period.
Global impacts of ENSO
Effects of El Nino on U.S. winter temperature and precipitation: Warm temperature around Great Lakes, Heavy rainfall in California and Gulf coast
Land-sea temperature contrasts: seasonal monsoon