El Niño- Southern Oscillation
ENSO
Ocean-atmosphere interaction
Changes in ocean circulation
Changes in atmospheric conditions
ENSO
Combined effects
ENSO
Begins in equatorial Pacific, but affects much larger area
Including Florida
Occurs every 2-7 years
Surface ocean temperatures
Distribution of rain patterns (drought/flooding)
Nutrient distributions (fishing)
ENSO
Southern Oscillation
Normal conditions
Trades blow east to west across equatorial Pacific
High pressure in the eastern Pacific
Low pressure in the western Pacific (Indonesian Low)
Low/High Pressure
Western Pacific
Indonesian Low
Warm pool in western Pacific
Water transported across the Pacific in the equatorial region (heated)
Water heats air
Warm air rises near Indonesian/Australia
Low pressure
Rain
Eastern Pacific
High pressure
Cold current plus upwelling
Air is cold à
low pressure
Southern Oscillation
What would happen if the pressure gradient across the equatorial Pacific decreased?
Trade wind strength?
Equatorial current strength?
Location of the Western Pac warm pool?
Equatorial countercurrent strength?
Shift in the relative pressure across the Pacific
Decrease in pressure gradient
Decrease in trade wind strength
or
- Reversal of trade wind direction
El Niño
Trade winds carry warm water across the Pacific
Off Peru- cold current
Plus coastal upwelling
Named for anomalous warm current off Peru at Christmas time during ENSO years
Normal Conditions
* Low pressure over Indonesia
* High pressure in east Pacific
* Strong trade winds
* Weak equatorial counter current
* Strong upwelling near Peru (Calif)
* Western Pacific ~8C warmer than east
* Rain in western Pacific
* Dry in the eastern Pacific
ENSO Years
* Higher pressure over Indonesia
* Lower pressure over eastern Pac
* Decreased pressure gradient across the equatorial Pacific
* Weaker trade winds (or reversed)
* Stronger counter current
Transports warm water to the east
* Reduced upwelling
* Shift in rainfall to the east
Development of ENSO
Quasi periodic (2-7 yrs)
- Duration ~1 yr, but variable
- ~1 event every 4 years for past century, and 1 strong event per decade
Prolonged ENSO conditions
Global effects
Shift in fish distribution patterns (tropical fish up to Alaska)
- Decreased nutrients off Peru (less upwelling)- collapse of anchovy industry
Drought off Australia
Rain Peru/California
- NW North America- higher temperatures
ENSO and Florida
ENSO
Cause?
Probably ocean/atmosphere interactions
Driving energy comes from the Western Pacific warm pool
ENSO
Contains the "seeds of its own destruction"
Western Pacific warm water moves across the ocean as a wave
Sets up a slower, weaker reflection
Alters thermocline depths
Leads to re-establishment of the pressure gradient
ENSO
Where are we today?
1997-1998 = strong ENSO
Florida wet and cold
Spring 1998- Dec. 2000 = La Nina
Florida warm and dry
Today — El Nino building in Pacific