ENSO IN NEUTRAL PHASE:
SSTs REMAIN COOL ACROSS THE EASTERN EQUATORIAL PACIFIC






 Sea-Surface Temperatures (SSTs) and Mixed-Layer Conditions:
The above average Sea-Surface Temperature (SST) anomalies associated with the 2006/2007 El Niño diminished in February and March, signaling the end of the warm event. However, warmer than average SSTs persisted in the far western equatorial Pacific west of the Date Line in March. Water temperatures in the equatorial mixed-layer also declined in March, 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 persisted and slowly propagated eastward in March.

For the month, the SST anomaly in the Niño 3.4 Index region was -0.11°C (-0.20°F), which was a change of -0.17°C (-0.31°F) compared to the February anomaly. The SSTs in the Niño 4 Index region of the western equatorial Pacific warmed during March to a monthly anomaly of +0.67°C (+1.21°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 March 2007.

Due to the rapid decrease in the SST anomalies in the Niño 3.4 index region, the 3-month running mean decreased below +0.5°C (+0.9°F) by the end of March. (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 and conditions had transitioned to neutral. The latest ENSO update from the Australian Bureau of Meteorology (BoM) also reflected the transition from a warm event to neutral ENSO conditions in the equatorial Pacific basin (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 March.

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

Pacific sea levels measured by the NASA/JPL Jason-1 satellite were below average across the eastern and central equatorial Pacific, reflecting the cooler-than-average ocean surface temperatures that have developed in this region in late February and March (see the most recent image of 26 March 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 March. 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 March was +0.8 W m-2 averaged across an area in the western Pacific near the Date Line between 160° E and 160° W. Therefore, the March value was positive but near-neutral, reflecting the neutral ENSO conditions.

Note: 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 -0.4 in March. The SOI has shown considerable variability during the recent 2006/2007 El Niño event, although it has shifted toward more neutral values over the first three months of 2007 as the event dissipated and transitioned to a neutral phase [note that consistently negative (positive) values of the SOI are typical of El Niño (La Niña) conditions].

Note, the SOI will likely transition to positive values over the next several months as NOAA's Climate Prediction Center (CPC) has forecasted a possible development of La Niña (cold event) conditions during April-June 2007.

Citing This Report

NOAA National Centers for Environmental Information, El Nino/Southern Oscillation for March 2007, published online April 2007, retrieved on May 5, 2024 from https://www.ncei.noaa.gov/access/monitoring/monthly-report/enso/200703.