chapter - Atmospheric and Oceanic Science

Low-frequency variability
during the subsequent months to establish an opposite sign pattern in July (+) . LNrelated
SST anomaly patterns for the CPDO regime (Fig. 14.8) feature significant
negative SST anomalies in the central and eastern equatorial Pacific and along the
West coast of the United States and significant positive anomalies in the North
Pacific during the period from September (0) to May (+) . This pattern resembles that
one associated with the PDO (Zhang et al. 1997). The positive centre in the North
Pacific keeps almost the same intensity and moves from the western North Pacific
to the central North Pacific from September (0) to July (+) .
Fig. 14.8. As Fig. 14.7, except for CPDO regime.
14.5. SLP composites
Since ENSO-related SLP patterns show considerable monthly variations, the
analyses for this parameter are done for the period from October (0) to March (+) , when
ENSO-related rainfall patterns present the largest anomalies. EN-related SLP patterns
for the WPDO regime show the largest anomalies in the tropics with the negative
values in the central and eastern Tropical Pacific and the positive values prevailing
in the Australasian and/or in the Atlantic/African regions (Fig. 14.9). The
areas with the largest anomalies which take part in the East-West pressure balance
are centred, in latitude, at the equator. Consequently, these areas define an anomalous
Walker circulation in the equatorial vertical zonal plane. Although the longitudinal
location and the intensity of the anomalous Walker circulation vary monthly,
it is strong and well established in the Australasian-Pacific sector during most
months of the period from October (0) to March (+) .
192