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HOME > Expert Assessments > Climate Diagnostics Bulletin > Tropical Highlights

Tropical Highlights - April 2007

Tropical sea surface temperatures (SSTs) during April 2007 were near-average across the western and central equatorial Pacific and colder-than-average over the eastern tropical Pacific (Fig. T18). This pattern is reflected in negative values of the Niņo 1+2   (-1.1) and Niņo 3 (-0.3) SST indices, and by a near-zero (+0.1) value of the Niņo 3.4 SST index (Table T2). Meanwhile, the Tahiti – Darwin SOI has been slightly negative since February 2007, and was -0.4 in April (Table T1, Figs. T1). These conditions are consistent in indicating a continuation of ENSO-neutral conditions.

The equatorial oceanic thermocline during April, measured by the depth of the 20ēC isotherm, featured a continuation of below-average depths over the eastern equatorial Pacific and near-average depths across the western and central equatorial Pacific (Figs. T15, T16). As a result, temperatures in the eastern equatorial Pacific remained generally 2-5ēC below average at thermocline depth (Fig. T17).

The low-level easterly winds during April remained stronger than average over the central equatorial Pacific (Fig. T20). This pattern has been very persistent since February, and is consistent with the anomalously shallow thermocline farther east. It is also consistent with the observed patterns of anomalous tropical convection, with enhanced convection over the western equatorial Pacific and suppressed convection across the central and eastern equatorial Pacific (Figs. T25, E3). In the subtropics and tropics, the 200-hPa atmospheric circulation anomalies were consistent with this pattern of anomalous tropical convection, with anticyclonic anomalies straddling the equator over the western Pacific, and cyclonic anomalies straddling the equator in the vicinity of the date line (Fig. T22).

For the latest status of the ENSO cycle see the ENSO Diagnostic Discussion at:


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