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Tropical Highlights - January 2002

The evolution toward a Pacific warm episode continued during January as an area of SST anomalies exceeding +1.0°C developed near the date line (Fig. T18) and the corresponding Niño-4 region SST index increased to +0.7 (Fig. T5, Table T2). Positive SST anomalies exceeding 0.5°C have prevailed in the Niño-4 region since September. However, negative SST anomalies have persisted across the east-central and eastern equatorial Pacific during that time, as indicated by continued negative SST index values in both the Niño-3 and Niño 1+2 regions (Fig. T18, Table T2).

Accompanying this evolution deep tropical convection extended across the central equatorial Pacific to between 160°E- 180° during January (Fig. T8). This location represents the farthest eastward extent of the deep tropical convection recorded since mid-1998 (Fig. T8 top, Fig. T25). However, equatorial convection has remained absent east of the date line throughout this 3 ½ year period (Fig. T25 top), which has contributed to the persistence of cyclonic streamfunction anomalies at 200-hPa in the subtropics of both hemispheres (Fig. T22 bottom) flanking the region of suppressed convection [indicated by negative anomalies of outgoing longwave radiation].

Tropical convection and the associated atmospheric circulation anomalies have also exhibited strong intraseasonal variability during the past several months (Figs. T11, T12, T13). MJO-related tropical convection during January was enhanced over the Indian Ocean and suppressed over Indonesia (Fig. T25).

The sea level pressure (SLP) pattern during January featured positive anomalies across the equatorial Pacific and Atlantic Ocean, and negative anomalies over the Indian Ocean and Indonesia (Fig. T19). This anomalous wave-1 pattern represents a reversal in phase from that observed in December, and was associated with a return to positive values of both the Tahiti - Darwin Southern Oscillation Index (SOI) (0.4) (Table T1) and the equatorial SOI (0.7).

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