and oceanic indices during January 2008 indicated a further strengthening of
mature cold episode (La Niña) conditions throughout the tropical Pacific.
This strengthening is highlighted by a decrease in the Niño 4 sea
surface temperature (SST) index to -1.5 for the first time since February 1999,
and in the Niño3.4 region, where the index dropped to -1.8, the lowest value
since January 2000. Overall,
equatorial sea surface temperatures (SSTs) anomalies were more than 2.0°C below
average across parts of the central and east-central equatorial Pacific (Fig.
T18). The magnitude of the negative SST anomalies
has decreased along the South American coast, as shown by an increase in the
negative values in Niño 1+2 index region (Table
T2, Fig. T5).
these surface conditions, the oceanic thermocline during January remained
shallower than normal across the equatorial Pacific east of 160°W and continued
to deepen in the region west of the International Date Line (Fig.
with this structure, sub-surface temperature departures remained negative across
the eastern equatorial Pacific, with temperatures at thermocline depth -2°C to
-5°C below average, while remaining above average west of 170°W (Fig.
Strong low-level easterly
anomalies and upper-level westerly anomalies persisted across the central
equatorial Pacific during the month (Figs. T20 and T21,
which is consistent with the shallower-than-average thermocline in the central
and eastern equatorial Pacific (Figs. T15,
T16). These conditions were associated with
enhanced convection (above-average rainfall amounts) over the far western
tropical Pacific and a continuation of suppressed convection (below-average
rainfall amounts) across the central and eastern equatorial Pacific (Figs.
T25, T26, E3).
Consistent with these anomalies, the
– Darwin SOI remained strongly positive for the second month in a row (+1.9)
Fig. T1) while the equatorial SOI remained above
+2.0 (Fig. T2).
An important player across the
global tropics during January 2008 was the continuation of the strongest and
longest-lived MJO activity since the Mar-Apr-May period of 2005. Coherent
eastward propagation of the MJO is seen in time-longitude sections of anomalous
OLR (Fig. T11)
and 850-hPa zonal wind (Fig. T13).
Although convection was suppressed during the month as a whole across the Indian
Ocean and parts of Indonesia, January saw enhanced convection and associated
westerly wind anomalies shift from Indonesia to the Date Line (south of the
equator) and later re-enter the Indian Ocean. Suppressed conditions shifted from
during the month. Weakened easterlies across the western Pacific associated
with this MJO activity initiated a strong oceanic Kelvin wave during the middle
of the month.
the latest status of the ENSO cycle see the ENSO Diagnostic Discussion at: