of global tropical sea surface temperature (SST) during April 2005 featured
negative anomalies in the eastern equatorial Pacific and near-average SSTs
elsewhere. The SST anomaly in the Niņo 3.4 region remained 0.4 during April
and the Niņo 1+2 anomaly remained negative, with an April value of -0.6 (Fig.
T18, Table T2). Meanwhile, atmospheric
features continued to show month-to-month variability associated with
intraseasonal (Madden-Julian Oscillation - MJO) activity (Figs. T11,
T12, T13, Table T1).
- Darwin SOI (latest value -1.0, Table T1, Fig.
T1) was negative, primarily in response to
higher-than-average pressure over
thermocline, measured by the depth of the 20°C
isotherm, remained deeper than average across the central and east-central
equatorial Pacific and slightly shallower than average in the eastern
equatorial Pacific during April (Figs. T15, T16).
Consistent with these conditions, oceanic temperatures at thermocline depth
above average across the central and east-central equatorial Pacific and
near normal in the eastern equatorial Pacific (Fig. T17).
low-level (850-hPa) and upper-level (200-hPa) equatorial zonal wind indices,
the Tahiti-Darwin SOI and the outgoing longwave radiation (OLR) index have
all exhibited considerable variability since January 2004 in association
with intraseasonal (Madden-Julian Oscillation) activity (Table T1).
low-level winds were observed over most of the tropical regions during April
2005, except for over the western (west-central) equatorial Pacific, where
strong low-level westerly (easterly) anomalies (more than 3.0 m s-1)
were observed (Fig. T20). This pattern is
consistent with enhanced convection over the western and west-central
tropical Pacific (between 140oE and the dateline) (Fig. T25).