Oscillations and teleconnections - The Global Climate System: Patterns, Processes, and Teleconnections - page 47

Indian Ocean, a distinct QB MSLP signal can be seen to evolve and propagate
in a northeasterly direction, again with indications of dynamical links to the
underlying SST structure. As in White and Tourre ( 2003 ), these MSLP structures
occur in conjunction with a slow eastward propagation of co-varying surface
temperature features, with the main interruption being found in the central to
eastern tropical Pacific, where they bifurcate around the tongue of surface
temperature of the opposite sign indicative of equatorial Pacific ENSO activity.
A distinct LF ENSO MSLP propagation from the southern Pacific to North
Atlantic is again evident in Figure 2.8 (Plate 2 ), but the signal does not
propagate beyond the western North Atlantic in the 90 degree phase diagram.
A distinct MSLP signal propagating from the southern Indian Ocean across
Australasia and into the northwestern Pacific is also seen again in the LF ENSO
sequence. As with the QB surface temperature sequence, the LF sequence
displays an eastward traveling signal and its bifurcation around the ''classical''
warm and cold SST tongues covering the central to eastern tropical Pacific.
The slowest propagation of signals is found in the quasi-decadal sequence,
with both the apparent movement of MSLP features from the Pacific to North
Atlantic and Indian Ocean across Australasia again being evident. The east-
ward movement of surface temperature signals is less organized, and the
equatorial Pacific tongue structures seen in the QB and LF ENSO sequences
have been replaced by more of a tropical central Pacific response linked to
higher latitudes along the western coast of North America.
2.8.3 PDO/IPO modes and patterns
Two climatic phenomena operating on inter- to multidecadal time frames
with distinct implications for ENSO have received particular attention in
recent times, the PDO, defined over the North Pacific by Mantua and Hare
( 2002 ), and the IPO, defined over the full Pacific basin and examined in a
coupled model by Arblaster et al.( 2002 ). Proxy data have also been used to
provide a long temporal record in which to investigate the PDO and its
characteristics (Cole et al. 2000 ; Villalba et al. 2001 ). The patterns of global
SSTs linked to both the PDO and IPO are shown in Figure 2.10a (Plate 4 a ).
According to the recent work of Folland et al.( 2002 ) the PDO and the IPO
appear to be essentially the same, and display signatures at several frequen-
cies (Mantua and Hare 2002 ) suggestive of a phenomenon ranging across a
broad frequency band. Using near-global observational data, Allan ( 2000 )
resolved the IPO as occurring in a frequency band of around 20-30 years,
producing a close match to the IPO pattern and time series (Arblaster et al.
2002 ) but also detected an interdecadal signal operating at around 15-20
years (as seen in Figure 2.6 ). Focusing on the Pacific basin, the lowest
frequency signal examined by Tourre et al.( 2001 ) is of a climatic feature