NEUTRAL CONDITION IS EXPECTED IN NEAR SPRING AND SUMMER

April 2, 2004

Since mid-September 2003, SST anomalies increased
in the central and eastern equatorial Pacific. A weak warm water fluctuation occurred during the
period of October and December. However, SST anomalies decreased evidently since
the end of last year. Neutral condition is expected during spring and summer of 2004.

1. Recent
Atmospheric and Oceanic Conditions

(1)   Sea Surface Temperature

After 2002/03 warm episode,
warmer-than-average condition maintained in the equatorial
Pacific to the west of the
dateline. In mid-September, unusual warm water strengthened and
extended eastward, and SST anomalies increased in the
eastern equatorial Pacific (Fig. 1). SST anomalies were above 0.5℃ in most
parts of the central and eastern equatorial Pacific during October. The SST indices of Nino 1+2+3+4 were
over 0.5℃ for
three months (Fig. 2). SST anomalies exhibited a decreasing trend
during recent
months and showed near normal condition in the
equatorial Pacific in
March.

(2)
Subsurface
Temperature

Since last
summer, most subsurface region of the central and western equatorial
Pacific was dominated
by warmer-than-average condition,
with the warm center remaining near the dateline. Cooler-than-average
water strengthened in the eastern equatorial Pacific since January
(Fig. 3).

(3)
Sea Level

Sea level distribution
exhibited that positive anomalies were in the western equatorial Pacific and negative anomalies
were in the eastern equatorial Pacific.

(4)
Wind Field

Since late September 2003, westerly anomalies occurred several times at the lower troposphere (850hPa)
over the equatorial Pacific, but they did not last long. Easterly anomalies remained
near the dateline for a long time. (Fig. 4).

(5)
Southern Oscillation

SOI maintained slight negative during 2003. Since the end of the year, it
fluctuated remarkably (Fig. 2).

(6)
Convections over the Tropics

The convective activities over the equatorial Pacific were near normal after
2002/03 warm episode.

2. Outlook

(1) Historical records of ENSO cycle
in last 50 years show that when a weak warming occurs during autumn in the central
and eastern equatorial Pacific, it is most likely that near normal condition will
maintain in the next spring and summer.

(2) Although SST anomalies
have displayed a decreasing trend, subsurface temperature anomalies and sea
level anomalies do not indicate that SST anomalies will continue to decrease.

(3) Strong westerly anomalies were
observed throughout the equatorial Indian Ocean and the
western equatorial Pacific recently. This suggests that SST anomalies are
possible to increase in the near future.

(4) A majority of the
dynamical and statistical models predicted that near-normal or slightly warmer-than-average
conditions prevail up to August 2004.

In general, near normal condition is expected before autumn
2004.

Fig. 1   Time-longitude
section of SST anomalies (℃) for 5°N - 5°S

Fig. 2  Time series of monthly SSTA
indices of NINO 1+2+3+4 and SOI

Fig. 3  Distribution of equatorial
depth-longitude section

of ocean temperature
anomalies (℃) for Mar. 2004
(20days)

Fig. 4  Time-longitude section of 850hPa zonal wind anomalies（m/s）for 5°N - 5°S