El Niño Wrap-Up
CURRENT STATUS as at 4th February 2003:
The period to the end of March is the period when the impact from El Niño on Australian rainfall most commonly breaks down with a return to average to above average totals. There are four points to note regarding this: (a) there are no guarantees - it may be after March; (b) this is not a prediction of when the drought will break, as that may take several months of sustained above average falls in some areas; (c) in all likelihood the breakdown will not occur uniformly across all drought affected areas; (d) the main El Niño indicators (SOI, sea-surface temperatures, trade winds) may return to neutral values a few months after the change in Australian rainfall patterns.
The El Niño continues to show signs of weakening. The sea surface temperature anomalies decreased over most of the tropical Pacific and there was a further reduction in the strength and the vertical extent of the subsurface ocean temperature positive anomalies in the central and eastern Pacific. The SOI for January (–2) rose by nine points from its December value (–11). Over the past week, cloudiness decreased around the dateline, and the Trade Winds remained fairly close to average over much of the Pacific. Given the trends during the past month in the main indicators, it may only be a matter of a few months until the Pacific has returned to a near-neutral state.
BOM ENSO Update (2-4-02)
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Anonymous
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Sea-surface temperature anomalies for January 2003 show that most of the central to eastern tropical Pacific was more than 1°C above average, with a few small patches more than 2°C above average. However the latest weekly data show that sea surface temperature anomalies continue to decrease over most of the tropical Pacific. NINOs 2, 3 and 4 indices dropped by 0.1 to 0.4°C, while NINO1 rose by 0.3°C and NINO3.4 remained almost unchanged. The NINO 3 value of +0.6°C is below the El Niño threshold of +0.8°C. The 7-day SST anomaly map shows the area of anomalies of more than +1°C further weakened in the central equatorial Pacific but somewhat spread to the east.
The subsurface data for January show a further reduction in the strength of the positive anomalies in the eastern half of the Pacific, as well as a decrease in the vertical extent of these anomalies. This is related to the eastward propagation along the thermocline of weak negative anomalies that have undercut the region of abnormally warm water. Negative anomalies slightly strengthened in the western Pacific.
An archive of past SST and sub-surface temperature charts is available.
In terms of developments in the atmosphere, the Southern Oscillation Index (SOI) for January (–2) was nine points above its December value (–11) (SOI graph, SOI table).
During El Niño episodes, there is often a general weakening of the Trade Winds across much of the tropical Pacific. Although there was some waxing and waning about the mean, the Trades were generally close to average over much of the Pacific during the past week. The TAO/TRITON map above for the past five days shows near average Trade Winds apart from a small patch of westerly anomalies near the warmest water at 175°W.
Cloudiness near the dateline in the central Pacific is another important indicator of El Niño as it normally increases during these episodes. Cloudiness near the dateline was mostly enhanced during January. Although there was some reduction in the cloudiness over the past week, it remained above average nevertheless.
The surveyed computer predictions for the Pacific are now in favour of an end to the El Niño during the next two to four months with nine of the 11 models indicating neutral conditions in June. These predictions are broadly consistent with the historical record, which indicates that El Niño events tend to break down in late summer or autumn. There are only two models persisting the current warmth into the middle of 2003. All models should be viewed cautiously as they're predicting across the so called "predictability barrier" between March and June.
Sea-surface temperature anomalies for January 2003 show that most of the central to eastern tropical Pacific was more than 1°C above average, with a few small patches more than 2°C above average. However the latest weekly data show that sea surface temperature anomalies continue to decrease over most of the tropical Pacific. NINOs 2, 3 and 4 indices dropped by 0.1 to 0.4°C, while NINO1 rose by 0.3°C and NINO3.4 remained almost unchanged. The NINO 3 value of +0.6°C is below the El Niño threshold of +0.8°C. The 7-day SST anomaly map shows the area of anomalies of more than +1°C further weakened in the central equatorial Pacific but somewhat spread to the east.
The subsurface data for January show a further reduction in the strength of the positive anomalies in the eastern half of the Pacific, as well as a decrease in the vertical extent of these anomalies. This is related to the eastward propagation along the thermocline of weak negative anomalies that have undercut the region of abnormally warm water. Negative anomalies slightly strengthened in the western Pacific.
An archive of past SST and sub-surface temperature charts is available.
In terms of developments in the atmosphere, the Southern Oscillation Index (SOI) for January (–2) was nine points above its December value (–11) (SOI graph, SOI table).
During El Niño episodes, there is often a general weakening of the Trade Winds across much of the tropical Pacific. Although there was some waxing and waning about the mean, the Trades were generally close to average over much of the Pacific during the past week. The TAO/TRITON map above for the past five days shows near average Trade Winds apart from a small patch of westerly anomalies near the warmest water at 175°W.
Cloudiness near the dateline in the central Pacific is another important indicator of El Niño as it normally increases during these episodes. Cloudiness near the dateline was mostly enhanced during January. Although there was some reduction in the cloudiness over the past week, it remained above average nevertheless.
The surveyed computer predictions for the Pacific are now in favour of an end to the El Niño during the next two to four months with nine of the 11 models indicating neutral conditions in June. These predictions are broadly consistent with the historical record, which indicates that El Niño events tend to break down in late summer or autumn. There are only two models persisting the current warmth into the middle of 2003. All models should be viewed cautiously as they're predicting across the so called "predictability barrier" between March and June.
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