The ENSO Cycle: Recent Evolution, Current Status and Predictions

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The ENSO Cycle Recent Evolution, Current Status
and Predictions
Vernon E. Kousky Climate Prediction Center / NCEP
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Outline

• Overview
• 2001-2002 Developments
• Current Conditions
• El Niño Outlook
• Typical U.S. Impacts and seasonal outlooks
• Summary

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Overview

• A Pacific basin warm (El Niño) episode is in
  progress in the tropical Pacific.
• Statistical and coupled model forecasts indicate
  that the El Niño will continue through the
  northern winter 2002-2003 and into the spring
  2003.
• All of the forecasts indicate that this El Niño
  will be considerably weaker than the 1997-98 El
  Niño.
• Impacts on the United States are expected during
  this fall and winter, but they should be
  generally weaker than those experienced during
  the very strong 1997-98 El Niño.

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2001-2002 Developments

• A transition from La Niña to a developing
  warm-episode (El Niño) began in mid-2001. An
  evolution toward a basin-wide El Niño occurred
  during December 2001-January 2002.

Time
Longitude
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2001-2002 Developments

• Early El Niño impacts occurred along the coasts
  of Ecuador and northern Peru during
  February-April 2002.
• During March-June 2002 the equatorial easterlies
  gradually weakened, while the Southern
  Oscillation Index (SOI) became persistently
  negative. These features indicated a developing
  El Niño.

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Time Series Nino 3.4, EQSOI, U850
LN
Positive SST departures Negative
EQSOI Weaker-than-normal equatorial easterly
winds
neutral
EN
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Subsurface Temperature Anomaly Index
T2
T1
Index of Upper Ocean Heat Content T1 T2 Index
of Anomalous Thermocline Slope T2 T1
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Heat Content Leads SST Anomalies
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2001-2002 Developments

• El Niño conditions established during April-June
  2002.

NOAAs Definition for El Niño Sea surface
temperatures 0.5C above average or greater,
averaged over three consecutive months, in the
Niño 3.4 region (120W-170W, 5N-5S).
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Current Conditions in the Tropical Pacific

• Ocean surface temperatures remain greater than
  1C (2F) above average throughout the central
  and east-central equatorial Pacific between 180W
  and 105W.

SST Anomalies 15 SEP-12 OCT 2002
Precipitation Anomalies September 2002
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Current Conditions in the Tropical Pacific
Equatorial ocean subsurface temperatures remain
above normal (deeper than normal oceanic
thermocline), with anomalies (departures from
average) exceeding 2C over much of the central
and east-central Pacific during September.
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El Niño Outlook

• Statistical and coupled model forecasts indicate
  that El Niño conditions will continue through the
  remainder of 2002 and into northern spring 2003.
• All of the forecasts indicate that this El Niño
  is expected to be considerably weaker than the
  1997-98 El Niño.

Courtesy Tony Barnston
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Typical Global El Niño Impacts

Region Period Impact
Indonesia Life of event Drier
Northeast Brazil March-May Drier
Central America /Mexico May-October Drier
West Coast South America March-May Wetter
Central South America June-December Wetter
Southeast Africa December-February Drier
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Typical El Niño impacts on North America

• El Niño impacts on North America are typically
  strongest during the winter and early spring.
  Impacts include
• Fall
• Pacific Northwest -- drier than normal
• Winter/Early Spring
• Northern Tier of States, western and central
  Canada, southern/southeastern Alaska - warmer
  than normal
• Northern Rockies, Ohio Valley drier than normal
• Southern Tier of States wetter than normal
• Texas eastward to the Carolinas cooler than
  normal

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Seasonal OutlooksNov 2002 - Jan 2003
Temperature
Precipitation
Outlooks combine typical El Niño impacts and
long-term trends.
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Seasonal OutlooksFeb - Apr 2003
Temperature
Precipitation
Outlooks combine typical El Niño impacts and
long-term trends.
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Summary

• El Niño conditions are evident in the tropical
  Pacific.
• Statistical and coupled model forecasts indicate
  that El Niño conditions will continue through the
  end of 2002 and into the first half of 2003.
• Some impacts on the United States are expected,
  starting in the fall 2002, but they should
  generally be weaker than those during the very
  strong 1997-98 El Niño.