Transcript What are the El Nino and La Nina?

What Are the El Nino and La Nina?
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
The Tropical Atmosphere Ocean (TAO)
buoy array by NOAA
Tropical mean state: Sea surface temperature (SST)
Indo-Pacific
warm pool
Eastern Pacific
cold tongue
2 basic
regions
Tropical mean state: Precipitation
Inter-tropical convergence
zone (ITCZ)
Strong rainfall
(heating)
Weak rainfall
GPCP Annual Mean Precipitation for 1979-2005 (mm/day)
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
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
Tropical mean State: Ocean-atmosphere
feedback
• Interacts with underlying
Pacific Ocean with
stronger upwelling
(cooling) in the east,
leading to a positive
feedback.
Video: Chasing El Nino
https://www.youtube.com/watch?v=TYR3GcSLHco
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
Evolution of the 1997-1998 El Nino event
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 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
Land-sea Contrast: Seasonal “Monsoon”
Seasonal temperature
distributions:
• T over land > water in summer
• T over land < water in winter
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
World’s major monsoon systems
From Jay Fein
1987
Seasonal variation of monsoon rainfall
Impacts of monsoons:
(1) Normal year
Dry season
Wet season
Impacts of monsoons:
(2) Failure of monsoon and droughts
Drought affected area in Karnataka, India, 2012,
image from Wikipedia
Impacts of monsoons:
(3) Excessive monsoon and floods
Image from Doctors without Borders
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