E l Nino-Southern Oscillation ENSO Richard H. Grumm and Paul Knight V_ February March 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 REGIMES but temperature anomalies tell the real story …. ELNINOELNINO LANINALANINA NEUTRALNEUTRAL

TROPICAL PACIFIC TEMPERATURE ANOMALIES desribe ENSO phases 100W160E180160W140W120W ELNINOELNINO LANINALANINA NEUTRALNEUTRAL

T D 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 T D PRESSURE DIFFERENCE ? <0

SOI- SOUTHERN OSCILLATION INDEX LA NINA T D 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 T WARMER 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 branch of jet stream Seasonably cool Unusually warm X X

El Nino- warm phase of ENSO

El Nino- The warm phase of SO Typically lasts 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 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 2 1 NINO 3.4- best teleconnection region W

RECENT EL NINO/ LA NINA

Evolution SST and Anomalies Nov 03-Feb 04

Nina region SST Anomalies Mar 2003-Jan lysis_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 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 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 First successful El Niño Forecast 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) El Nino: – the strongest on record in terms of amplitude – broke the 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).