# Presentation: 439526

## A Review of Monthly/ Seasonal Climate Variability for 2005-2006: The ENSO Cycle

**Vernon E. Kousky**
**NOAA/Climate Prediction Center **
**October 23, 2006**

## Outline

** ****Recent Evolution & Current Conditions**
** ****Historical Perspective**
** ****Pacific SST Outlook**
** ****Summary**

## Evolution of Equatorial Pacific SST Departures

**Evolution of Equatorial Pacific SST Departures**

**Longitude**

**Time**

**During late 2005-early 2006 SST anomalies decreased and below-average temperatures developed throughout most of the central and eastern equatorial Pacific. **
**In February 2006 positive SST anomalies developed in the extreme eastern equatorial Pacific, similar to what occurred  during the La Niña** **years** **1999, 2000 and 2001****.**
**Since May 2006, positive SST anomalies have increased across the equatorial Pacific between 160E and the South American coast.**

## Tropical OLR and winds: 22 Feb-19 Mar 2006

**Tropical OLR and winds: ****22 Feb-19 Mar 2006**

**Negative OLR anomalies (enhanced convection and precipitation, blue shading) were observed over northern Indonesia, northern Australia and the Philippines, and in the vicinity of Hawaii.  **
**Positive OLR anomalies (suppressed convection and precipitation, orange shading) were observed over the central equatorial Pacific and over the NH eastern tropical Pacific. **

**Low-level easterly wind anomalies were observed over the central and western equatorial Pacific between 155E and 140W. **

**The patterns of anomalous OLR and wind were consistent with La Ni****ña conditions.**

**Upper-level westerly wind anomalies were observed over the equatorial Pacific between 150E and 115W.  Cyclonic circulation anomalies (indicated by C in the figure) were observed north and south of the equator over the central tropical Pacific. **

**C**

**C**

**C**

**C**

## Niño Indices: Evolution

**The latest weekly SST anomalies are positive (between +0.8C and +1.2C) in all of the Niño regions****. **

## EQ. Pacific Upper-Ocean (0-300 m) Heat Content & SST Anomalies

**Decreasing upper-ocean heat content was observed during July 2005 through January 2006. Beginning in early February upper ocean heat content increased and, since early April heat content anomalies have been positive.  **

**Decreasing SST anomalies were observed during late 2005 through January 2006. Beginning in late March anomalies increased and, since late May positive anomalies have been observed.  **

## Upper-Ocean Conditions in the Eq. Pacific

**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 ****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 most recent values of the upper-ocean heat anomalies (positive) and the thermocline slope index (near zero) indicate the early stages of El Niño.**

**Cold Episodes**
**Warm Episodes**

**Themocline slope index is the difference in the anomalous depth of the 20C isotherm  between the western Pacific (160E-150W) and the eastern Pacific (90-140W).**

## Recent 4-Week Average SST Anomalies in the Tropical Pacific

**Equatorial ocean surface temperatures were greater than 0.5****o****C above average across the equatorial Pacific between 160oE and the South American coast. Departures exceeded +1oC between 165oE and 145oW, and between 85oW and 125oW. **
**17 September-14 October 2006**

## Global SST Departures (Deg C): 17 September-14 October 2006

**The equatorial SSTs are above average everywhere except in the vicinity of Indonesia. The subtropical Atlantic basin (5-25N) has been warmer than average for more than a year.** **Positive anomalies dominate the high latitudes in the North Atlantic Ocean and west-central North Pacific Ocean. **

## Tropical OLR and winds: last 30 days

**Tropical OLR and winds: last 30 days**

**Negative OLR anomalies (enhanced convection and precipitation, blue shading) were observed between the date line and Papua/ New Guinea, and over the southwest North Pacific.  **
**Positive OLR anomalies (suppressed convection and precipitation, orange/red shading) were observed over western Indonesia, portions of Malaysia and the eastern Indian Ocean.**

**Westerly anomalies (weaker-than-average easterly winds) were observed near the equator between Papua New Guinea and the Date Line (180W). Equatorial low-level winds were near average east of the Date Line.**

**The pattern of anomalous OLR over the equatorial Pacific during the last 30 days reflects the early stages of El Ni****ño. **

**Easterly upper-level (200hPa) equatorial zonal wind anomalies were observed over Indonesia and the western Pacific west of the Date Line. **
**Westerly anomalies were observed over the extreme eastern equatorial Pacific.**

## Heat Content Evolution in the Eq. Pacific

**The downwelling (upwelling) phase of Kelvin waves is indicated by the dashed (dotted) lines. Downwelling (upwelling) produces an increase (decrease) in upper-ocean heat content.**

**Heat Content Evolution**** ****in the Eq. Pacific**

** ****The upper-ocean heat content gradually decreased in the eastern and central equatorial Pacific and increased in the extreme western equatorial Pacific during mid-2005. as a precursor to weak La Niña conditions that developed in late 2005.**
** ****During March-April 2006 the upper-ocean heat content increased as La Niña conditions weakened and ENSO-neutral conditions became established. **
** ****The basin-wide warmth, as observed in recent months, is usually observed prior to and in the early stages of El Ni****ño.**
** ****Throughout this period variability in heat content has been present due to weak Kelvin wave activity.**

**Time**

**Longitude**

## Subsurface Conditions in the Eq. Pacific

**Subsurface Conditions**** ****in the Eq. Pacific**

**Time**

**Longitude**

**Most recent pentad analysis**

** ****During August-September 2006 ****positive subsurface temperature anomalies were observed throughout the equatorial Pacific. A pattern of basin-wide positive subsurface temperature departures is usually observed prior to and in the early stages of El Ni****ño.**
** ****The most recent analysis shows positive anomalies, between the surface and 200 m depth, across most of the equatorial Pacific. **

## 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**

**Weaker-than-average easterlies (orange/red shading). **
**Stronger-than-average easterlies (blue shading).**

**Low-level easterly winds have averaged weaker than normal over the western equatorial Pacific between 130E and 170E.  **
**Since July, anomalous westerly winds have also dominated the east-central equatorial Pacific. **

## 200-hPa Velocity Potential Anomalies (5N-5S)

**200-hPa Velocity Potential Anomalies (5N-5S)**

**Negative anomalies (green shading) indicate favorable conditions for precipitation.**

**Positive anomalies (brown shading) indicate unfavorable conditions for precipitation.**

**Longitude**

**Time**

**In early March the MJO activity weakened and became incoherent.**
**Weak MJO activity was evident during May- early August 2006. **
**Since early September MJO activity has intensified.**

## 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**

**Since early August, suppressed convection has been persistent over the eastern Indian Ocean and Indonesia. **
**Recently, enhanced convection has developed over the western tropical Pacific.**

## ONI: Evolution since 1950

**ONI: Evolution since 1950**

**The most recent ONI value (July-September 2006) is 0.4C****. **

**El Ni****ñ****o**

**La Ni****ña**

**neutral**

## Niño 3.4 evolution – Comparison for El Niño episodes

**Most recent Ni****ño**** 3.4 values (heavy black line) compared to values for 14 historical El Ni****ño episodes. On the time axis year 0001 is the first year of a warm episode.**

- Recent Niño 3.4 values, derived from ERSST.v2, lie in the lower half of the distribution of historical El Niño episodes since 1950.

## Niño 3 evolution – Comparison for El Niño episodes

**Most recent Ni****ño**** 3 values (heavy black line) compared to values for 14 historical El Ni****ño episodes. On the time axis year 0001 is the first year of a warm episode.**

- Recent Niño 3 values, derived from ERSST.v2, lie in the middle of the distribution of historical El Niño episodes since 1950.

## Niño 4 evolution – Comparison for El Niño episodes

**Most recent Ni****ño**** 4 values (heavy black line) compared to values for 14 historical El Ni****ño episodes. On the time axis year 0001 is the first year of a warm episode.**

- Recent Niño 4 values, derived from ERSST.v2, lie in the upper half of the distribution of historical El Niño episodes since 1950.

## Niño 1+2 evolution – Comparison for El Niño episodes

**Most recent Ni****ño**** 1+2 values (heavy black line) compared to values for 14 historical El Ni****ño episodes. On the time axis year 0001 is the first year of a warm episode.**

- Recent Niño 1+2 values, derived from ERSST.v2, lie in the upper half of the distribution of historical El Niño episodes since 1950.

## Pacific Niño 3.4 SST Outlook

**Pacific Ni****ño 3.4 ****SST Outlook**

- Figure provided by the International Research Institute (IRI) for Climate and Society (updated 18 October 2006).

## SST Outlook: NCEP CFS  19 October 2006

- The CFS ensemble mean (blue line) indicates El Niño conditions through NH spring 2007.

## Summary

** ****The recent atmospheric circulation and precipitation patterns indicate weak El Niño conditions in the tropical Pacific Ocean.**
** ****SST anomalies are between +0.8C and +1.2C in all of the Niño regions. **
** ****Based on recent trends and a majority of the statistical and coupled model forecasts El Ni****ñ****o conditions should intensify during the next 3-4 months and will likely continue through April-June 2007.**