El Niño/Southern Oscillation - February 2007


Sea-Surface Temperatures (SSTs) and Mixed-Layer Conditions:
The above average Sea-Surface Temperature (SST) anomalies associated with the 2006/2007 El Niño diminshed over the past month, signaling the end of the warm event. However, warmer than average SSTs persisted in the far western equatorial Pacific from approximately 160°E to 170°W in February. Water temperatures in the equatorial mixed-layer also declined in February, with a large area of -3.0°C (+3.6°F) and cooler temperature anomalies between 50-150 meters depth in the eastern equatorial Pacific. This layer of cooler water continued to develop and slowly propagated eastward in February.

For the month, the SST anomaly in the Niño 3.4 Index region was +0.06°C (+0.11°F), which was a decrease of -0.64°C (-1.15°F) compared to the January anomaly. The SSTs in the Niño 4 Index region of the western equatorial Pacific also cooled during February to a monthly anomaly of +0.42°C (+0.76°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 February 2007.

Despite the rapid decrease in the SST anomalies in the Niño 3.4 index region, at the end of February the 3-month running mean remained above +0.5°C (+0.9°F). (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 the 2006/2007 warm event (El Niño) had dissipated by the end of February. The latest ENSO forecast from the Australian Bureau of Meteorology (BoM) also reflected the transition from a warm event to neutral ENSO conditions in the equatorial Pacific basin over the past month (see the Australian BoM ENSO Wrap-Up).

Equatorial Zonal Winds (U-Component Winds) and Sea-Level Topography:
The easterly Trade winds were above normal across the central and eastern equatorial Pacific during February.

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 February zonal winds. A period of anomalous westerly flow occurred in the far western equatorial Pacific region during early February, as easterly Trade winds were stronger-than-average across most of the central and eastern equatorial Pacific basin during the past month.

Pacific sea levels measured by the NASA/JPL Jason-1 satellite were below average across the central equatorial Pacific in February, reflecting the cooler-than-average ocean surface temperatures that have developed in this region (see the most recent image of 27 February 2007 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 February. A region of negative OLR anomalies was measured in the far western equatorial Pacific near Indonesia, west of the Date Line, illustrating the enhanced tropical convection observed in this region over the past month.

The monthly OLR index for February was +0.1 W m-2 averaged across an area in the western Pacific near the Date Line between 160° E and 160° W. Therefore, the February value was near-neutral, and was also the first month with a positive index value following six consecutive months with negative OLR indices.

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 -0.5 in February. The SOI has shown considerable variablity during the 2006/2007 El Niño event, although it was negative for the first three months of 2007. Before this, the SOI was negative for six consecutive months during the formative phase of the most recent El Niño [note that consistently negative (positive) values of the SOI are typical of El Niño (La Niña) conditions].

A transition to near-neutral SOI values, and potentially postive monthly values, is possible over the next several months as NOAA's Climate Prediction Center (CPC) has forecasted a transition from neutral to La Niña conditions during April-June 2007.

Citing This Report

NOAA National Climatic Data Center, State of the Climate: El Niño/Southern Oscillation for February 2007, published online March 2007, retrieved on July 22, 2014 from http://www.ncdc.noaa.gov/sotc/enso/2007/2.