El Niño/Southern Oscillation - August 2006
WEAK EL NIÑO CONDITIONS DEVELOP:
SSTs WARM ACROSS THE EQUATORIAL PACIFIC
SSTs WARM ACROSS THE EQUATORIAL PACIFIC
Temperatures (SSTs) and
A large area of Sea-Surface Temperature (SST) anomalies greater than +0.5°C (+0.9°F) stretched from the central Pacific to the South American coast, with anomalies greater than +1.0°C (+1.8°F) near 180°W. Water temperatures in the mixed-layer also continued to warm in August, with a large area of +1.0°C (+1.8°F) temperature anomalies as deep as 150 meters in the central Pacific.
For August, the SST anomaly in the Niño 3.4 Index region was +0.38°C (+0.68°F), which was an increase of +0.27°C (+0.49°F) compared to the July anomaly. The SSTs in the Niño 4 Index region of the western equatorial Pacific also continued to warm during August, resulting in a monthly anomaly of 0.58°C (1.04°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 August 2006.
With warmer SSTs in the Niño 3.4 index region in August, the 3-month running mean in this region was above average for the third month in a row, but remained short of 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 ENSO Diagnostic Discussion indicated that a warm event (El Niño) had developed by early September, but the future strength of the event is uncertain at this time. The Australian Bureau of Meteorology (BoM) has a slightly more conservative forecast for the evolution of the current conditions (see the Australian BoM ENSO Wrap-Up).
||Equatorial Zonal Winds (U-Component
Winds) and Sea-Level Topography:
The monthly averaged easterly trade winds remained near-normal across much of the eastern and central equatorial Pacific during August, with only a small area of negative U-component anomalies in the eastern Pacific (reflective of slightly stronger than average easterlies).
Weaker than normal easterly winds persisted near the Date Line again in August as evidenced by positive U-component anomalies. There was considerable week-to-week variability as shown in the loop of August zonal winds.
Pacific sea levels measured by the NASA/JPL Jason-1 satellite were slightly above-average along the equatorial zone in August, reflecting the warmer than average ocean temperatures (see the 22 August 2006 sea level anomalies image to the left).
Longwave Radiation (OLR):
The map to the left shows the spatial pattern of global OLR (in W m-2) observed by satellite during August. The absence of strong positive or negative OLR anomalies (typically associated with La Niña and El Niño, respectively) is indicative of the presence of neutral ENSO conditions.
The monthly OLR index for August was -0.3 W m-2 averaged across an area in the western Pacific between 160° E and 160° W. This was only the second time this year that the index was below the long-term mean. If conditions continue to evolve toward an El Niño episode, the OLR Index will continue to decrease as convection in the central and eastern equatorial Pacific increases.
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
The standardized SOI was negative in August, with a monthly averaged value of -1.6 for the month, a further decrease from the value of -0.8 in July. August was the fourth consecutive month with a below average SOI. Note that consistently negative (positive) values of the SOI are typical of El Niño (La Niña) conditions, and a further decrease of this index will likely occur as the current El Niño episode develops over the next few months.