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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