In the context of recent La Niña conditions, this section displays a comparison figure of historic La Niña events since 1949 vs. current conditions. The most recent (January-February) MEI value has increased dramatically (now at -1.34), almost 0.4 standard deviations below last months value. Its rank has risen (now 4th, up from 12th), clearly above the
strong La Niña threshold for this season, and the lowest Jan-Feb MEI value since 1976. In fact, all three stronger La Niña values for Jan-Feb occurred in the 1970s (1971, '74, and '76).
Negative
SST anomalies cover the equatorial Pacific from just east of New Guinea to just west of Galapagos (
SST near the South American coast has warmed considerably in the last few months, and could be considered a LOCAL
El Niño situation). A large fraction of the negative
SST anomalies reach close to -2C, similar to last month's summary
latest weekly SST map. More or less stable La Niña conditions have been in place since late August 2007.
For an alternate interpretation of the current situation, I recommend reading the
latest NOAA ENSO Advisory which represents the official and most recent Climate Prediction Center opinion on this subject. In its latest update (March 6, 2008), strong La Niña conditions were diagnosed and expected to continue, albeit at a weaker levvel, through at least May 2008. There are several other
ENSO indices that are kept up-to-date on the web. Several of these are tracked at the
NCEP website that is usually updated around the same time as the MEI. Niño regions 3 and 3.4 have shown persistent temperature anomalies of -1.5C or lower since October (region 3) and December (region 3.4). The last time region 3.4 featured negative anomalies as big as the most recent value (-1.9C) was in January 1989. For extended Tahiti-Darwin
SOI data back to 1876, and timely monthly updates, check the
Australian Bureau of Meteorology website. This index caught on to the current La Niña event last November, reaching +14 (1.4 sigma) in both December and January, and higher yet (+21) in February. The average for the last two months (+17.1) is second only to Jan-Feb 1974 for this season. Thus, the
SOI is now in sync with other
ENSO indices in terms of assessing this event, following an extended period of apparently erratic behavior since about the middle of 2006. An ever longer Tahiti-Darwin
SOI (back to 1866) is maintained at the
Climate Research Unit of the University of East Anglia website, however with less frequent updates (currently more than one year behind). Extended
SST-based
ENSO data can be found at the
University of Washington-JISAO website, currently updated through April 2007.
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