ENSO
El Ni単o La ni単a +
TheSouthern Oscillation by ROBERT PERRY
El Ni単o
IN SPANISH, EL NIÑO MEANS “The Child” WITH A CAPITOL “C,” REFERRING TO THE BABY JESUS. WHAT DID THE CHRIST CHILD HAVE TO DO WITH THE NAME OF THIS OCEANATMOSPHERE PHENOMENON? IT’S ORIGINAL NAME WAS GIVEN BY PERUVIAN COASTAL INHABITANTS AND FISHERMEN WHO NOTICED A PERIODIC RECURRENCE OF WARM OCEAN WATER AND A CORRESPONDING DECLINE IN PREFERRED FISH SPECIES. SINCE THE EFFECTS WERE MOST COMMON AROUND CHRISTMAS, THE NAME “El Niño” WAS GIVEN.
NORMAL PREVAILING SURFACE CURRENTS IN
HOT POOL COLD TONGUE
UNDER “NORMAL” CONDITIONS, THE TROPICAL TRADE WINDS BLOW EAST TO WEST AND CAUSE WARM SURFACE WATERS TO ACCUMULATE IN THE WESTERN PACIFIC. NOTICE ALSO THAT THE HUMBOLDT CURRENT WHICH RUNS UP THE COAST OF SOUTH AMERICA BRINGING COLD WATER TOWARDS THE EQUATOR, CREATES A COLD TONGUE AS IT MOVES AWAY FROM LAND.
HOT POOL
COLD TONGUE
NORMAL UPWELLING “NORMAL” CONDITIONS
HOT POOL SHIFTS EAST NO COLD TONGUE
HOT POOL SHIFTS EAST
TRADE WINDS DIMINISH
NO COLD TONGUE
NO UPWELLING EL NIﾃ前 CONDITIONS
EL NIﾃ前 CONDITIONS: THE TRADE WINDS HAVE BACKED OFF AND SO HAS THE NORMAL EAST TO WEST EQUATORIAL CURRENT. NOW, AS THE WARMER-THAN-NORMAL WATER APPROACHES THE WEST COAST OF THE AMERICAS, THE THERMOCLINE TAKES A DRASTIC DIVE AND SHUTS DOWN THE UPWELLING PROCESS WHICH BRINGS FERTILIZER TO THE SURFACE AND FUELS THE FOOD WEB. THIS IS NOT GOOD FOR MARINE LIFE ALONG THE WEST COAST OF THE AMERICAS.
HOT POOL SHIFTS WEST EXTENDED COLD TONGUE
HOT POOL SHIFTS WEST
EXTENDED COLD TONGUE
HUGE UPWELLING LA NIÑA CONDITIONS
LA NIÑA CONDITIONS: DEPRESSED SEA LEVELS ALONG THE AMERICAS CREATE A HUGE UPWELLING. VAST AMOUNTS OF DEEP, COLD AND NUTRIENT RICH BOTTOM WATERS ARE RETURNED TO THE ILLUMINATED SURFACE. PHOTOSYNTHESIS RATES SKYROCKET, AND THE FOOD WEB IN THE OCEAN NEAR PERU BLOSSOMS. MEANWHILE THE HOT, ELEVATED SURFACE WATERS AND ALL THEY BRING WITH THEM LIE TO THE FAR WEST.
SST’s ( C) O
ENSO LINKING ATMOSPHERE AND OCEAN
Storms move westward
South America Australia
STRONG UPWELLING
La Niña
SO HERE’S THE WAY IT WORKS: HOT WATER EVAPORATES AND SENDS A LOT OF MOISTURE INTO THE ATMOSPHERE. THIS RETURNS TO THE SURFACE AS RAINFALL. ON THE OTHER HAND, COLD WATERS EVAPORATE VERY LITTLE AND CARRY NO MOISTURE INTO THE ATMOSPHERE. CONDITIONS ARE DRY. HOT WATER MEANS WET, COLD MEANS DRY. SO IN THIS ILLUSTRATION, A LA NINA PERIOD, THE HOT WATER POOL IN THE WEST MEANS HIGHER THAN NORMAL RAINFALL THERE, WHILE COLD WATERS TO THE EAST SPELL DROUGHT FOR THE AMERICAS.
Walker circulation
South America Australia
Region of Upwelling
Storms move eastward
South America Australia
Upwelling suppressed
BIOLOGICAL IMPORTANCE of UPWELLING
Normal Trade Winds cause Causes cold tongue to extend west
Deep, cold & nutrient rich waters
NORMAL CONDITIONS SUPPORT COASTAL UPWELLING.
SUNLIGHT PHOTIC ZONE
ONLY UPWELLING CAN RETURN THE FERTILIZING NUTRIENTS TO THE PHOTIC ZONE
NORMAL CONDITIONS SUPPORT COASTAL UPWELLING.
EL NIﾃ前 SUPRESSES COASTAL UPWELLING, REDUCES NUTRIENTS & CAUSES SURFACE POPULATIONS TO DISAPPEAR.
MEASURING AND PREDICTING El Ni単o, La Ni単a and The Southern Oscillation 1. BUOY DATA
The Tropical Atmosphere Ocean (TAO) Project
ARGOS satellite
Moored buoy
MEASURING AND PREDICTING ENSO USING SATELLITE DATA 2. TOPEX /Poseidon
Birth of the 1997 El Nino
El ~ Nino
La ni単a
~ El Nino
~ La Nina
~
Jan. 1997 - El Nino is coming ! A= normal cold water upwelling off Peru. B= Kelvin wave of hot water moving to the East.
~ Sept. 1997 - El Nino conditions !
~ May 1998 - La Nina is coming !
(0-10S)(90W-80W) Southern hemisphere: Equatorial S. American coast. (5N-5S)(150W-90W) Equator: mid-Pacific to S. American coast. (5N-5S)(160E-150W) Equator: Australia to mid-Pacific. (5N-5S)(170-120W) Equator: western Pacific to mid-Pacific.
ENSO – YEAR BY YEAR
THE EFFECTS OF
EL NIﾃ前
Normal Rainfall
~ El Nino Rainfall
TreeRing Growth
EN EN Approximately 25% of the 23,000 pups born in June 1997 at San Miguel Island died.
3 Feb 98 GOES Infrared STATE
RAIN ENGLFED THE ENTIRE OF CALIFORNIA AT THE END OF THE 1997-98 EL NIﾃ前
February 1998 Record Rainfall Amounts (inches): Location Total Former Record/Year Ukiah 22.33 19.49 in 1958 Santa Barbara 21.74 * 17.33 in 1962 UCLA 20.51 * 18.37 in 1918 Chatsworth 20.11 * 17.71 in 1962 Oxnard 17.80 15.58 in 1962 Simi Valley 17.20 * 11.15 in 1992 Northridge 15.75 * 14.23 in 1962 Monterey 15.00 11.68 in 1978 San Francisco 14.89 12.52 in 1878 L.A. Cvc Ctr 13.68 13.37 in 1884 L.A. Airport 13.30 11.07 in 1962 Lompoc 12.86 11.54 in 1918 Redwood City 12.46 10.06 in 1986 Santa Maria 11.59 9.69 in 1962 Long Beach 11.22 9.66 in 1937 * Denotes an all-time-record February monthly total.
El Ni単o - Summary The term El Ni単o means 'Christ Child' and was first used by Peruvian fishermen in the late 1800's to describe the warm current appearing off the western coast of Ecuador and Peru around Christmas time. Today El Ni単o describes the warm phase of a naturally occurring sea surface temperature oscillation in the tropical Pacific Ocean. When this warming occurs the usual upwelling of cold, nutrient rich deep ocean water is significantly reduced. Sometimes an extremely warm event can develop that lasts for much longer time periods. In the 1990s, strong El Ni単os developed in 1991 and lasted until 1995, and from fall 1997 to spring 1998. This oscillation is associated with the atmosphere, and thus the term ENSO - which incorporates the southern oscillation phenomenon - is commonly used.
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