Tropical Highlights - February 2004
Sea surface temperature (SST) anomalies were near-average across the
equatorial Pacific east of the date line and slightly warmer than average in
the western Pacific (Fig. T18, Table T2). Atmospheric indices
continued to exhibit large month-to-month variability associated with intraseasonal (Madden-Julian Oscillations - MJO)
activity (Figs. T11, T12, T13, Table T1).
Since November 2003, SST anomalies have decreased across the entire equatorial Pacific (Fig. T9), with
the values observed in Niņo 1+2, Niņo 3, and Niņo 4 the lowest since September 2003 (Table T2).
The oceanic thermocline, measured by the depth of the 20°C
isotherm (Figs. T15, T16) was deeper than average in the central and
east-central equatorial Pacific and shallower than average in the eastern Pacific. Consistent with these
conditions, oceanic temperatures at thermocline depth were 3-4°C above average in the central equatorial Pacific
and 2-3°C below normal in the eastern Pacific (Fig. T17).
The monthly low-level (850-hPa) and upper-level (200-hPa) equatorial
zonal wind indices and the outgoing longwave radiation (OLR) index have exhibited considerable variability since
November 2003 in association with intraseasonal activity (Table T1). During
February, stronger-than-average low-level easterly winds were observed over the central Pacific
(Fig. T20), while stronger-than-average westerly winds were observed over
the central Pacific at upper levels (Fig. T21).
Tropical OLR anomalies were negative (enhanced cloudiness and
precipitation) over the western Pacific and northern Australia, and positive over the central tropical Pacific, with
near-zero anomalies throughout the rest of the global Tropics (Fig. T25). Although
convection over the central Pacific has exhibited increased variability due to intraseasonal activity, there has been
a tendency for suppressed convection since November 2003 (Fig. T11).
The Tahiti-Darwin SOI was 1.1 during the February (Table
T1, Fig. T1). This index has exhibited large month-to-month variability, in
response to strong MJO activity (Fig. T10). The equatorial SOI has
exhibited less variability during the past few months, with the index remaining between 0.5 and 0.9 since November
2003 (Fig. T2).