chapter - Atmospheric and Oceanic Science

14.4. SST composites
Low-frequency variability
The sequential EN-related SST anomaly composites for the WPDO regime
(Fig. 14.5) show significant positive SST anomalies over the central and eastern
equatorial Pacific and along the West coast of the United States and significant negative
anomalies in the North Pacific for the period from September (0) to May (+) . This
pattern is similar to that associated with the PDO (Zhang et al. 1997). It is worthwhile
noting that the negative centre in the North Pacific intensifies from
November (0) to January (+) , and remains quite strong until July (+) . On the other hand,
EN-related significant positive SST anomalies for the CPDO regime (Fig. 14.6) are
confined to central and eastern equatorial Pacific. In this case, the positive anomalies
remain quite strong until January (+) , when they start to weaken to almost disappear
in May (+) . So, ENSO-like SST anomaly structure lasts longer for EN years
of the WPDO regime than for EN years of the CPDO regime. This result is consistent
with the reestablishment of positive rainfall anomalies in the southern and
southeastern Brazil in April (+) and in the southeastern Brazil in May (+) for EN years
of the WPDO and with very small rainfall anomalies in these same areas and
months for EN years of the CPDO regime.
Fig. 14.5. Monthly El Niño-related mean SST anomalies for the WPDO regime for the indicated months.
Contour interval is 0.3°C, with negative (positive) contours being dashed (continuous). Light to dark blue
(yellow to red) shading encompasses negative (positive) values which are significant at the 95% confidence
level. The zero contours have been omitted.
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