El Nino-Southern Oscillation ENSO Richard H. Grumm and Paul Knight V_2.2 10 February 2004 26March 2002
E l Nino-Southern Oscillation ENSO Richard H. Grumm and Paul Knight V_2.2 10 February 2004 26March 2002.
Dec 17, 2015
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El Nino-Southern OscillationENSO
Richard H. Grummand
Paul KnightV_2.2
10 February 2004 26March 2002
Introduction
• ENSO is flow regime over the Pacific basin hinged on the distribution of sea surface temperatures– There are two phases the warm and cold
phase and a third neutral phase– The warm and cold phases get most
peopled attention
• ENSO affects the Walker Circulation which– Teleconnects to weather elsewhere
Two Phases:El Nino/La Nina
• ANOMOLOUS POOL OF WARM WATER APPEARS ACROSS THE TROPICAL CENTRAL/EASTERN PACIFIC
• ANOMOLOUS POOL OF COOL WATER APPEARS ACROSS THE TROPICAL CENTRAL/EASTERN PACIFIC
The well known El Nino Teleconnection
the temporal fluctuation about globe associated with El Nino
How El Nino Teleconnects
Walker Circulation impacts
TROPICAL PACIFIC TEMPERATURE REGIMESbut temperature anomalies tell the real story….
ELNINO
LANINA
NEUTRAL
TROPICAL PACIFIC TEMPERATURE ANOMALIESdesribe ENSO phases
100W160E 180 160W 140W 120W
ELNINO
LANINA
NEUTRAL
TD
The SOUTHERN OSCILLATION
PRESSURE DIFFERENCES BETWEEN DARWIN AND TAHITI
Initially related to weather patterns in Australia and India.by Sir Herbert Walker
SOUTHERN OSCILLATION
EL NINO
TD
PRESSURE DIFFERENCE ? <0
SOI- SOUTHERN OSCILLATION INDEX
LA NINA
TD
PRESSURE DIFFERENCE ? >0
SST ANOMALIES/ SOI INDEX
WHAT IS THE RELATIONSHIP HERE ??
El Nino- Warm phase of ENSO
• What causes an El Nino to occur?– Trade winds in C/W Pacific weaken ->> (why?) Kelvin/Rossby wave
theory– Warm water “sloshes” back eastward– Warm water appears in eastern
tropical Pacific since upwelling weakens
El Nino- Warm phase of ENSO
• Tropical Oceanic effects of El Nino:– Positive SST anomalies of 2-6 C occur
from 180 degrees to South America coast (80W)
– Small negative SST anomalies in far western Pacific
– Fishing industry
OCEANIC TEMPERATURE CHANGES DURING EL NINO
D TWARMER
Cooler
Implies higher pressure at cooler Darwin than warmer Tahiti
El Nino- Warm phase of ENSO
• Atmospheric effects of El Nino:– TROPICAL LATITUDES
• SHIFTS the WALKER CIRCULATION
WALKER CIRCULATION
- SFC LOW PRS ANOMALY OVER E/C PACIFIC- SFC HIGH PRS ANOMALY OVER FAR WEST PACIFIC- ENHANCES CONVECTION OVER CENTRAL AND EASTERN PACIFIC- SUPRESSES CONVECTION OVER FAR WESTERN PACIFIC
El Nino- Mid-latitude impacts
• STRENGTHENS SOUTHERN JET STREAM ACROSS CENTRAL/EASTERN PACIFIC
• Impacts North America• No well documented impacts in Europe
El Nino- warm phase of ENSO
Enhances southern branchof jet stream
Seasonably cool
Unusually warm
X
X
El Nino- warm phase of ENSO
El Nino- The warm phase of SO
• Typically lasts 12-18 months• Occurs irregularly at intervals of 2
to 7 years• Sometimes is followed by La Nina• Greatest atmospheric impacts are
noted near the anomalies• Some mid-latitude impacts in
North American and eastern Asia
La Nina- The cold phase of ENSO
• What causes an La Nina to occur?– Good question!– El Nino is a rife with negative
feedbacks that allow for a return to Neutral and/or La Nina regimes?
La Nina- The cold phase of ENSO
• Tropical Oceanic effects of La Nina:– Negative SST anomalies of 1-4 C
occur from 180 degrees to South America coast (80W)
– Small positive SST anomalies in far western Pacific
– Fishing industry
D T
OCEANIC TEMPERATURE CHANGES DURING LA NINA
La Nina- The cold phase of ENSO
• Atmospheric effects of La Nina:– TROPICAL LATITUDES
• SHIFTS the WALKER CIRCULATION
WALKER CIRCULATION
- Surface High pressure ANOMALY OVER east/central PACIFIC (Tahiti)- Surface Low pressure ANOMALY OVER far western PACIFIC (Darwin)- ENHANCES CONVECTION OVER FAR WESTERN PACIFIC- SUPRESSES CONVECTION OVER EASTERN AND CENTRAL PACIFIC
La Nina- Mid Latitude Impacts
• PACIFIC JET STREAM IS MORE VARIABLE AND FARTHER NORTH– Less southern stream
storms and hence Pacific storms in southern North America
– More colder air into western North America
Comparison
La Nina- The cold phase of ENSO
• Typically lasts 12-18 months• Occurs irregularly at intervals of 2
to 7 years• Sometimes is followed by El Nino• Greatest atmospheric impacts are
noted near the anomalies• Recent history suggests occurring
less frequently than El Ninos
MEI of recent past…some El Nino’s pointed out.
T,v,q,p
NIÑO SST regions
21
NINO 3.4- best teleconnection region
4 3
140W
RECENT EL NINO/ LA NINA
Evolution SST and AnomaliesNov 03-Feb 04
Nina region SST Anomalies Mar 2003-Jan
2004http://www.cpc.ncep.noaa.gov/products/anal
ysis_monitoring/enso_advisory
SO values Feb 2003-Feb 2004
EL NINO & US PRECIPITATION
EL NINO & US TEMPERATURES
LA NINA-TEMP
LA NINA & US PRECIPITATION
Recent Events Impact• 1972-73 El Niño Event
– Was big but not a record, but global food problems occurred,– Russian wheat crisis brought El Niño to fore-front– US wheat to Russia and we grew too much soy…a
replacement food for anchoveta– Connections of bad weather and teleconnections to El Niño
grows
• 1982-83 Event: The big anomaly– thought to have been the El Niño of the Century until 1998– big global impacts on food and weather
• floods and droughts in tropics blamed on El Niño– flooding in Peru– droughts in Indonesia, Australia, north and south Africa
• eastern US warmest winter in 25 years
– value of long-lead forecasting grew in importance
More El Niños• 1986-87 First successful El Niño Forecast• 1990-95 A long El Nino Event
– a long slow El Niño– forecasts of its break-down were poor and wrong– may be one of the longest events document– was not an intense event– showed up consistent in NIÑO3.4 data– SOI was not as good an indicator (see P115 of Glantz)
• 1997-98 El Nino:– the strongest on record in terms of amplitude– broke the 1982-83 events intensity– followed closely by a strong La Niña– was forecast but not as well as you might think!
Conclusions
• ENSO is a circulation related to both the atmosphere and the oceans
• ENSO has has 3 phases• Warm- El Niño• Cold - La Niña•Neutral
• These phases impact Walker Circulation• this impacts global circulation patterns, which• teleconnect to climate anomalies around the world
Conclusions-II
• Today, better monitored with SST data – Niño3– Niño4– and now the better NIÑO3.4 area
• Coupled Ocean Models predictions• Forecasters should know general impacts• Consider interaction in North America of
ENSO and NAO.
MEI Components
• sea-level pressure (P), zonal (U) and meridional (V) components of the surface wind, sea surface temperature (S), surface air temperature (A), and total cloudiness fraction of the sky (C).
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