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 Niño 1+2, Niño 3, and Niño 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).