El Niño/Southern Oscillation - November 2006


EL NIÑO EVENT MATURES:
ABOVE NORMAL SSTs PERSIST ACROSS THE EQUATORIAL PACIFIC






Sea-Surface Temperatures (SSTs) and Mixed-Layer Conditions:
A large area of Sea-Surface Temperature (SST) anomalies greater than +1.0°C (+1.8°F) stretched from the western Pacific to the South American coast in November, with anomalies greater than +1.5°C (+2.7°F) near the Dateline between 170°E and 150°W. Water temperatures in the mixed-layer also continued to warm over the past month, with a large area of +3.0°C (+5.4°F) and greater temperature anomalies as deep as 150 meters in the central and eastern equatorial Pacific.

For the month of November, the SST anomaly in the Niño 3.4 Index region was +1.21°C (+2.18°F), which was an increase of +0.25°C (+0.45°F) compared to the October anomaly. The SSTs in the Niño 4 Index region of the western equatorial Pacific also continued to warm during November, resulting in a monthly anomaly of +1.26°C (+2.27°F) above the mean (map of Niño regions). For the most recent global ocean surface temperatures, please see the loop of satellite-derived weekly SST anomalies for November 2006.

With warmer SSTs in the Niño 3.4 index region in November, the 3-month running mean has surpassed the +0.5°C (+0.9°F) threshold that would indicate the onset of an El Niño episode (NOTE: For NOAA's official ENSO classification scheme, please see NOAA's El Niño/La Niña Index Definition). The Climate Prediction Center's most recent ENSO Diagnostic Discussion indicated that a warm event (El Niño) had developed by mid-September, and has continued to strengthen since that time. The ENSO forecast from the Australian Bureau of Meteorology (BoM) also continues to reflect the development of warm event conditions in the tropical Pacific basin (see the Australian BoM ENSO Wrap-Up).





Equatorial Zonal Winds (U-Component Winds) and Sea-Level Topography:
Anomalous westerly winds were observed across much of the western and central equatorial Pacific during November, while the easterly Trade winds were near-normal across the far eastern equatorial Pacific.

Significant week-to-week variability in the near-surface winds has been observed along the equatorial region of the Pacific over the past month, as shown in the loop of November zonal winds. A period of westerly flow occurred in the equatorial Pacific region during early November, followed by a return to near-normal easterly Trade winds across the eastern Pacific later in the month.

Pacific sea levels measured by the NASA/JPL Jason-1 satellite were above average across most of the equatorial Pacific in mid-November, reflecting the warmer-than-average ocean temperatures and the maturing El Niño event (see the most recent image of 20 November 2006 sea level anomalies).





Outgoing Longwave Radiation (OLR):
The map to the left shows the spatial pattern of global OLR (in W m-2) measured by satellite during November. A region of negative OLR anomalies was observed in the western equatorial Pacific near the Dateline, which suggests that enhanced tropical convection has begun to develop in this region.

The monthly OLR index for November was -0.2 W m-2 averaged across an area in the western Pacific between 160° E and 160° W. This was the fourth consecutive month that the OLR index was below the long-term mean, although an OLR Index value of -0.2 is considered near-neutral. Note that significantly negative OLR indices are typical of the mature phase of a warm event.

At present, NOAA's Climate Prediction Center (CPC) has forecasted the current El Niño episode to persist into 2007. Therefore, it is expected that the OLR Index will decrease further as the Walker Circulation shifts to the east and tropical convection in the central equatorial Pacific intensifies.

Note that high frequency variability in OLR is typically associated with the Madden-Julian Oscillation (MJO, which is convective activity that propagates west to east in the near-equatorial region from the Indian Ocean into the Pacific Ocean approximately every 30-60 days). The latest MJO activity can be seen in CPC's graphs of Daily MJO Indices.


Southern Oscillation Index (SOI):
The standardized SOI was near-neutral in November, with an averaged value of +0.1 for the month. The near-neutral SOI in November followed six consecutive months with negative index values. Note that consistently negative (positive) values of the SOI are typical of El Niño (La Niña) conditions. However, negative SOI values are expected to redevelop by the end of the year, as NOAA's Climate Prediction Center (CPC) continues to forecast the persistence of the current El Niño episode into the first few months of 2007.

Citing This Report

NOAA National Climatic Data Center, State of the Climate: El Niño/Southern Oscillation for November 2006, published online December 2006, retrieved on October 22, 2014 from http://www.ncdc.noaa.gov/sotc/enso/2006/11.