ENSO REPORT
No. 24
Apr. 2, 2005
BEIJING CLIMATE CENTER, CMA
NEUTRAL CONDITION IS EXPECTED TO CONTINUE IN THE CENTRAL AND EASTERN PACIFIC DURING THE SPRING AND SUMMER OF 2005
April 2, 2005
A weak warm water fluctuation occurred during the period fromSeptember 2004toJanuary 2005. Recently, SST anomalies exhibited near normal condition in the equatorial Pacific. ENSO-neutral conditions are expected to continue during the spring and summer of 2005.
1.Characteristic of the warm water fluctuation occurred in autumn 2004
Since July2004, SST anomalies increased in the central equatorial Pacific and extended eastward. The SST index of Nino1+2+3+4 was over 0.5℃ in September and reached the maximum of 0.8℃ in December. In the early of 2005, SST anomalies decreased quickly in the central and eastern equatorial Pacific, and negative SST anomalies were observed in the eastern Pacific. In February, SST index of Nino1+2+3+4 dropped to 0.2℃, which showed that the warm water fluctuation ended. This process lasted 5 months, and was a weak warm fluctuation (Fig.1, 2).
2. Recent Atmospheric and Oceanic Conditions
（1）Sea Surface Temperatures
During March, the equatorial Pacific SST anomalies returned to near normal generally. Above 0.5℃SST anomalies dominated the equatorial Pacific around the dateline. Meanwhile, below -0.5℃SST anomalies controlled the eastern equatorial Pacific (Fig.3). The indices of NINO 1+2+3+4 andNINO 3 were 0.1℃and -0.3℃, respectively.
（2）Subsurface Temperatures
Recently, abnormally warm water controlled most of the central equatorial Pacific while abnormally cold water dominated the eastern equatorial Pacific. The most recently monitoring results showed that the warm water extended eastward and upward slowly. This condition is unfavorable for sea surface temperatures decreasing widely and continually in the equatorial Pacific (Fig.4).
（3） Wind Field
During February, strong westerly anomalies(850hPa) controlled the central and western equatorial Pacific with central values above 8m/s, and continued to the first decade of March. From the second decade of March, easterly anomalies emerged in the equatorial Pacific west the dateline (Fig.5).
（4） Southern Oscillation
Recently, SOI fluctuated remarkably, it was 0.3 in January, and it dropped to –2.4 in February and rose to 0.3 in March (Fig. 2).
（5）Convections over the Tropics
During February, anomalous outgoing longwave radiation (OLR) distribution along the equator exhibited that convections were enhanced significantly around the dateline and suppressed over the western equatorial Pacific.
3. Outlook
(1) Although SST anomalies in the central and eastern equatorial Pacific have displayed a decreasing trend, strong westerly anomalies controlled the central and western equatorial Pacific during February and anomalous warm subsurface water extended eastward and upward slowly. These conditions are unfavorable for sea surface temperatures decreasing widely and continually in the equatorial Pacific.
(2) From the viewpoint of ENSO cycle, after a long warm-period (2002-2004) in the central equatorial Pacific, it is unfavorable for the central and eastern Pacific to enter a new abnormally warm stage in the near future. From the second decade of March, easterly anomalies emerged in the equatorial Pacific west to the dateline.Most recently, below -0.5℃SST anomalies controlled the eastern equatorial Pacific. Above conditions imply that there is little possibility for a warm event to occur in the near future.
(3) Most of the dynamicaland statistical models predict that near-normal conditions will prevail during the spring and summer of 2005.
(4) The consultation meeting on ENSO prediction was held on 25 March 2005 in BCC, more than 20 specialists from Peking University, Nanjing University, IAP/CAS, CAMS/CMA and BCC/CMA attended the meeting. After a careful analysis and lively discussion on recent conditions of tropical atmosphere and ocean, a conclusion was drawn that conditions of the tropical Pacific atmosphere and ocean would remain near normal in the spring and summer of 2005.
In general, neutral condition isexpected to continue in the central and eastern Pacific during the spring and summer of 2005.
Fig. 1 Time-longitude section of monthly SST anomalies(℃) for 5N - 5S
Fig.2 Monthly evolutions of Nino1+2+3+4 SSTa index (curve)and SOI (bar)
Fig.3 Distribution of SST anomalies (℃) forMar. 2005
Fig.4 Depth-longitude section of ocean temperature anomalies (℃) for 5N - 5S
Feb. 2005
Fig.5 Time-longitude section of 850hPa zonal wind anomalies（m/s）for 5N - 5S