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ENSO Cycle: Recent Evolution, Current Status and Predictions: 

ENSO Cycle: Recent Evolution, Current Status and Predictions Update prepared by Climate Prediction Center / NCEP May 14, 2007

Outline: 

Outline Overview Recent Evolution and Current Conditions Oceanic Niño Index (ONI) – 'Revised 1 March 2004' Pacific SST Outlook U.S. Seasonal Precipitation and Temperature Outlooks Summary

Overview: 

Overview The tropical Pacific is currently in an ENSO-neutral state. SST anomalies remain near-zero in the central equatorial Pacific and below average in the eastern equatorial Pacific. A majority of the statistical and coupled model forecasts indicate SST anomalies will become increasingly negative during the next several months. Subsurface conditions and recent CFS forecasts indicate a possible transition to La Niña conditions within the next 1-3 months.

Recent Evolution of Equatorial Pacific SST Departures (oC): 

Recent Evolution of Equatorial Pacific SST Departures (oC) Longitude Time The SST anomalies decreased rapidly in January everywhere east of the Date Line, and have since been below average for areas east of 140oW. Between May 2006 and December 2006, positive SST anomalies increased across the equatorial Pacific between 160ºE and the South American coast.

Niño Region SST Departures (oC) Recent Evolution: 

Niño Region SST Departures (oC) Recent Evolution Negative SST departures have recently strengthened across the eastern equatorial Pacific. The latest departures are nearly -1.0ºC in the Niño 3 region and -1.5ºC in the Niño 1+2 region. The SST anomaly is weakly negative in the Niño 3.4 region and remains slightly positive in the Niño 4 region.

SST Departures (oC) in the Tropical Pacific During the Last 4 Weeks: 

SST Departures (oC) in the Tropical Pacific During the Last 4 Weeks Equatorial SSTs during the last four weeks were more than 1ºC below average in areas between 120ºW and the South American coast, and 0.5oC above average in portions of the western Pacific.

Global SST Departures (oC) : 

Global SST Departures (oC) The equatorial SSTs are above average in most areas, except in the eastern Pacific Ocean. The tropical and high latitudes of the North Atlantic Ocean have been warmer than average since 1995. Positive anomalies dominate the middle latitudes in the western Indian Ocean and South Atlantic Ocean.

Weekly SST Departures (oC) for the Last Four Weeks: 

During April- May 2007 below-average SSTs persisted in the eastern equatorial Pacific Ocean. Over this 4-week period SST anomalies decreased over most of the eastern equatorial Pacific. Weekly SST Departures (oC) for the Last Four Weeks

Upper-Ocean Conditions in the Eq. Pacific: 

Monthly thermocline slope index, calculated as the difference in the anomalous depth of the 20ºC isotherm between the western Pacific (160ºE-150ºW) and the eastern Pacific (90º-140ºW). Upper-Ocean Conditions in the Eq. Pacific The basin-wide equatorial upper ocean (0-300 m) heat content is greatest prior to and during the early stages of a Pacific warm (El Niño) episode (compare top 2 panels) and least prior to and during the early stages of a cold (La Niña) episode. The slope of the oceanic thermocline is least (greatest) during warm (cold) episodes. The values of the upper-ocean heat anomalies (positive) and the thermocline slope index (negative) during the last half of 2006 indicated weak-to-moderate El Niño conditions. Cold Episodes Warm Episodes

Central & Eastern Pacific Upper-Ocean (0-300 m) Weekly Heat Content Anomalies: 

Central andamp; Eastern Pacific Upper-Ocean (0-300 m) Weekly Heat Content Anomalies Between early April 2006 and early January 2007 the heat content was above average, but showed intraseasonal fluctuations related to the MJO (see following slides). Since January 2007 the upper ocean heat content anomalies have been negative, indicating subsurface conditions are favorable for the development of La Niña.

Sub-Surface Temperature Departures (oC) in the Equatorial Pacific: 

Sub-Surface Temperature Departures (oC) in the Equatorial Pacific Time Longitude Most recent pentad analysis During March-April 2007 negative subsurface temperature anomalies were observed in the region east of the date line (180o). The most recent period (below) shows negative anomalies between the surface and 200 m depth across the eastern half of the equatorial Pacific Ocean.

Tropical OLR and Wind AnomaliesDuring the Last 30 Days: 

Tropical OLR and Wind Anomalies During the Last 30 Days Negative OLR anomalies (enhanced convection and precipitation, blue shading) were observed over portions of southeast Asia, the Philippines, Papua New Guinea, and along the South Pacific Convergence Zone (SPCZ). Areas of positive OLR anomalies were observed over the central and eastern tropical Pacific between the date line and 80ºW. Lower-level (850-hPa) easterly wind anomalies (stronger-than-average easterly winds) persisted near the date line. An upper-level (200-hPa) cyclonic anomaly couplet was observed in the subtropical eastern Pacific with westerly anomalies along the equator. L L

Atmospheric Circulation over the North Pacific & North America During the Last 60 Days: 

925-hPa Temp. Anoms. (oC) 200-hPa Wind 500-hPa Height andamp; Anoms. Atmospheric Circulation over the North Pacific andamp; North America During the Last 60 Days In late March, the Pacific jet stream was retracted westward and a trough developed over the North Pacific, leading to below-average temperatures in Alaska. Also, a 500-hPa ridge over western North America expanded over the contiguous United States contributing to mild temperatures. In early and mid April, the ridge over eastern North America was replaced by a trough and below-average temperatures in much of the contiguous United States. Recently, above average temperatures have returned to the United States and Canada in association with a 500-hPa ridge.

U.S. Temperature and Precipitation Departures During the Last 30 and 90 Days: 

U.S. Temperature and Precipitation Departures During the Last 30 and 90 Days 30-day (ending 12 May 2007) temperature departures (degree C) 90-day (ending 13 May 2007) % of average precipitation 90-day (ending 12 May 2007) temperature departures (degree C) Last 30 Days Last 90 Days 30-day (ending 13 May 2007) % of average precipitation

Intraseasonal Variability: 

Intraseasonal Variability Intraseasonal variability in the atmosphere (wind and pressure), which is often related to the Madden-Julian Oscillation (MJO), can significantly impact surface and subsurface conditions across the Pacific Ocean. Related to this activity significant weakening of the low-level easterly winds usually initiates an eastward-propagating oceanic Kelvin wave. Several Kelvin waves have occurred during the last year (see next slide).

Weekly Heat Content Evolution in the Equatorial Pacific: 

The warm phase of Kelvin waves is indicated by the dashed lines and the cold phase is indicated by dotted lines. Kelvin waves have alternating warm and cold phases. Down-welling and warming occur in the leading portion of a Kelvin wave, and up-welling and cooling occur in the trailing portion. Weekly Heat Content Evolution in the Equatorial Pacific Time Longitude Downwelling Upwelling El Niño conditions and anomalously high heat content (red) were present during the latter part of 2006. Month-to-month variability in heat content during May 2006 – January 2007 is due to Kelvin wave activity. Recently, upper-ocean temperature departures have become persistently negative in the eastern equatorial Pacific. Below-average subsurface temperatures are usually found prior to La Niña.

Low-level (850-hPa) Zonal (east-west) Wind Anomalies (m s-1): 

Low-level (850-hPa) Zonal (east-west) Wind Anomalies (m s-1) Longitude Time Westerly wind anomalies (orange/red shading). Easterly wind anomalies (blue shading). In mid-December 2006, the low-level easterly winds strengthened over the central equatorial Pacific, and westerly wind anomalies developed over the eastern Indian Ocean and Indonesia. Easterly anomalies have persisted since January 2007 over the equatorial Pacific between 160ºE and 140ºW. Recently, the area of low-level easterly anomalies has expanded eastward.

200-hPa Velocity Potential Anomalies (5ºN-5ºS): 

200-hPa Velocity Potential Anomalies (5ºN-5ºS) Negative anomalies (green shading) indicate favorable conditions for precipitation. Positive anomalies (brown shading) indicate unfavorable conditions for precipitation. Longitude Time Weak MJO activity was evident during late November/ early December 2006. The MJO strengthened in mid-December 2006, but weakened in early January 2007. The MJO strengthened again in mid-February, but has since weakened.

Outgoing Longwave Radiation (OLR) Anomalies: 

Outgoing Longwave Radiation (OLR) Anomalies Wetter-than-average conditions (blue shading) Drier-than-average conditions (orange/red shading) Longitude Time During August-December, suppressed convection persisted over the eastern Indian Ocean and Indonesia. Enhanced convection developed near the date line in September and persisted through mid-December. In late December/ early January enhanced convection over the Indian Ocean shifted eastward across Indonesia and into the central Pacific. Since February, convection has been suppressed to the east of the Date Line and periodically enhanced in the western equatorial Pacific.

Oceanic Niño Index (ONI): 

Oceanic Niño Index (ONI) The ONI is based on SST departures from average in the Niño 3.4 region, and is a principal measure for monitoring, assessing, and predicting ENSO. Defined as the three-month running-mean SST departures in the Niño 3.4 region. Departures are based on a set of improved homogeneous historical SST analyses (Extended Reconstructed SST – ERSST.v2). The methodology is described in Smith and Reynolds, 2003, J. Climate, 16, 1495-1510. Used to place current conditions in historical perspective NOAA’s operational definitions of El Niño and La Niña are keyed to the ONI index.

NOAA Operational Definitions of El Niño and La Niña Conditions: 

NOAA Operational Definitions of El Niño and La Niña Conditions El Niño: characterized by a positive ONI greater than or equal to +0.5°C. La Niña: characterized by a negative ONI less than or equal to -0.5°C. To be classified as a full-fledged El Niño or La Niña episode these thresholds must be exceeded for a period of at least 5 consecutive months.

ONI (oC): Evolution since 1950: 

ONI (oC): Evolution since 1950 The most recent ONI value (February –April 2007) is +0.1oC. El Niño La Niña neutral

Historical El Niño and La Niña Episodes Based on the ONI computed using ERSST.v2: 

Historical El Niño and La Niña Episodes Based on the ONI computed using ERSST.v2

Historical Pacific warm (red) and cold (blue) episodes based on a threshold of +/- 0.5 oC for the Oceanic Nino Index (ONI) [3 month running mean of ERSST.v2 SST anomalies in the Nino 3.4 region (5N-5S, 120-170W)], calculated with respect to the 1971-2000 base period. For historical purposes El Niño and La Niña episodes are defined when the threshold is met for a minimum of 5 consecutive over-lapping seasons.: 

Historical Pacific warm (red) and cold (blue) episodes based on a threshold of +/- 0.5 oC for the Oceanic Nino Index (ONI) [3 month running mean of ERSST.v2 SST anomalies in the Nino 3.4 region (5N-5S, 120-170W)], calculated with respect to the 1971-2000 base period. For historical purposes El Niño and La Niña episodes are defined when the threshold is met for a minimum of 5 consecutive over-lapping seasons.        

Historical Pacific warm (red) and cold (blue) episodes based on a threshold of +/- 0.5 oC for the Oceanic Nino Index (ONI) [3 month running mean of ERSST.v2 SST anomalies in the Nino 3.4 region (5N-5S, 120-170W)], calculated with respect to the 1971-2000 base period. For historical purposes El Niño and La Niña episodes are defined when the threshold is met for a minimum of 5 consecutive over-lapping seasons.: 

Historical Pacific warm (red) and cold (blue) episodes based on a threshold of +/- 0.5 oC for the Oceanic Nino Index (ONI) [3 month running mean of ERSST.v2 SST anomalies in the Nino 3.4 region (5N-5S, 120-170W)], calculated with respect to the 1971-2000 base period. For historical purposes El Niño and La Niña episodes are defined when the threshold is met for a minimum of 5 consecutive over-lapping seasons.          

Historical Pacific warm (red) and cold (blue) episodes based on a threshold of +/- 0.5 oC for the Oceanic Nino Index (ONI) [3 month running mean of ERSST.v2 SST anomalies in the Nino 3.4 region (5N-5S, 120-170W)], calculated with respect to the 1971-2000 base period. For historical purposes El Niño and La Niña episodes are defined when the threshold is met for a minimum of 5 consecutive over-lapping seasons.: 

Historical Pacific warm (red) and cold (blue) episodes based on a threshold of +/- 0.5 oC for the Oceanic Nino Index (ONI) [3 month running mean of ERSST.v2 SST anomalies in the Nino 3.4 region (5N-5S, 120-170W)], calculated with respect to the 1971-2000 base period. For historical purposes El Niño and La Niña episodes are defined when the threshold is met for a minimum of 5 consecutive over-lapping seasons.       0.5 0.4 0.2 0.2 0.2 0.3 0.4 0.7 0.8 0.9 0.9 0.9 0.8 0.6 0.5 0.3 0.4 0.5 0.3 0.2 0.0 0.0 -0.2 -0.4 -0.7 -0.8 -0.7 -0.4 -0.2 0.0 0.1 0.3 0.4 0.7 0.9 1.1 1.1 0.8 0.3 0.1

Pacific Niño 3.4 SST Outlook: 

Most statistical and coupled model forecasts indicate slightly below-average SSTs in the Niño 3.4 region during the next three months, with ENSO-neutral conditions persisting through the period May-July 2007. However, a few methods indicate the possibility of La Niña developing within the next three months. Pacific Niño 3.4 SST Outlook Figure provided by the International Research Institute (IRI) for Climate and Society (updated 18 April 2007).

SST Outlook: NCEP CFS Forecast Issued 13 May 2007: 

SST Outlook: NCEP CFS Forecast Issued 13 May 2007 The CFS ensemble mean (heavy blue line) indicates a transition from neutral to La Niña conditions during the next 1-3 months.

U. S. Seasonal OutlooksMay-July 2007: 

U. S. Seasonal Outlooks May-July 2007 Temperature Precipitation Outlooks combine long-term trends and soil-moisture effects, along with typical ENSO impacts when appropriate.

Summary: 

Summary The tropical Pacific is currently in an ENSO-neutral state. SST anomalies remain near-zero in the central equatorial Pacific and below average in the eastern equatorial Pacific. A majority of the statistical and coupled model forecasts indicate SST anomalies will become increasingly negative during the next several months. Subsurface conditions and recent CFS forecasts indicate a possible transition to La Niña conditions within the next 1-3 months.

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