What Are the El Nino and La Nina?

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What Are the El Nino and La Nina?
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Review of last lecture

1. 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)
2. How upper level longwaves and shortwaves may
   enhance cyclonic development at the surface
   (upper level low to the west of surface low)
3. The three regions of cyclogenesis and typical
   tracks
4. Lake effect
5. Anticyclones, heat waves and droughts
6. Climate change move the tracks of the
   midlatitude cyclones towards the poles

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The Tropical Atmosphere Ocean (TAO) buoy array by
NOAA
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Tropical mean state Sea surface temperature (SST)
Indo-Pacific warm pool
Eastern Pacific cold tongue
2 basic regions
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Tropical mean state Precipitation
Inter-tropical convergence zone (ITCZ)
Strong rainfall (heating)
Weak rainfall
GPCP Annual Mean Precipitation for 1979-2005
(mm/day)
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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

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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

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Tropical mean State Ocean-atmosphere feedback

• Interacts with underlying Pacific Ocean with
  stronger upwelling (cooling) in the east, leading
  to a positive feedback.

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Movie time!

• Chasing El Nino

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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)

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Typical ENSO period is 3-7 years, but with
significant irregularity
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Evolution of the 1997-1998 El Nino event
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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
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El Nino effects on U.S. winter temperature
Warm temperature around Great Lakes
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El Nino effects on U.S. winter precipitation
Heavy rainfall
Heavy rainfall
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El Niño impacts on Peruvian fishing

• Large numbers of fish marine plants die as
  upwelling is reduced by weakened Ekman transport
  from weakened trades
• Reduce Peruvian anchovy fish catch

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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
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ENSO prediction
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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