El Niño/Southern Oscillation - October 2006
EL NIÑO CONTINUES TO DEVELOP:
SSTs INCREASE ACROSS THE EQUATORIAL PACIFIC
SSTs INCREASE ACROSS THE EQUATORIAL PACIFIC
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 in October, with anomalies greater than +1.0°C (+1.8°F) between 120°W and the South American coast. Water temperatures in the mixed-layer also continued to warm over the past month, with a large area of +1.0°C (+1.8°F) and greater temperature anomalies as deep as 150 meters in the central and eastern Pacific.
For the month of October, the SST anomaly in the Niño 3.4 Index region was +0.96°C (+1.73°F), which was an increase of +0.35°C (+0.63°F) compared to the September anomaly. The SSTs in the Niño 4 Index region of the western equatorial Pacific also continued to warm during October, resulting in a monthly anomaly of 0.86°C (1.55°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 October 2006.
With warmer SSTs in the Niño 3.4 index region in October, the 3-month running mean in this region was above average for the third month in a row, and 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 early September, but the future strength of the event remains uncertain at this time. The ENSO forecast from the Australian Bureau of Meteorology (BoM) also continues to reflect the development of warm event conditions in the Pacific basin (see the Australian BoM ENSO Wrap-Up).
Winds (U-Component Winds) and Sea-Level Topography:
Anomalous westerly winds were observed across much of the western and central equatorial Pacific during October, while the easterly Trade winds were weaker-than-normal across the 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 October zonal winds. A period of westerly flow in the equatorial region during early October gave way to stronger than normal easterly Trade winds later in the month.
Pacific sea levels measured by the NASA/JPL Jason-1 satellite were above average in the central and eastern tropical Pacific in October, reflecting the warmer-than-average ocean temperatures and the development of an El Niño event (see the 15 October 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 October. The lack of any large-scale tropical convection in the central and eastern equatorial Pacific suggests that the atmosphere has lagged the ocean during the formative phase of the current El Niño event.
The monthly OLR index for October was -0.8 W m-2 averaged across an area in the western Pacific between 160° E and 160° W. This was the third consecutive month that the OLR index was below the long-term mean.
At present, NOAA's Climate Prediction Center (CPC) : has forecasted the current El Niño episode to persist into early 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 and eastern 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.
Oscillation Index (SOI):
The standardized SOI was negative in October, with an averaged value of -1.7 for the month. Therefore, October was the sixth 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 persistence of negative SOI values will likely occur over the next few months as the current El Niño episode continues through the end of the year and into early 2007.