Oscillations and teleconnections - The Global Climate System: Patterns, Processes, and Teleconnections - page 43

temperatures on the QB time scale are dominated by a zonal gradient at
middle-higher latitudes between Europe and Asia, and a distinctly meridio-
nal gradient over the North American continent. An element of the meridio-
nal gradient in surface temperatures across North America is still evident in
the LF ENSO sequence, but the zonal pattern across Europe and Asia has
been replaced by coherent middle-higher latitude warming or cooling across
higher latitude Eurasia.
The MSLP evolution of both the QB and LF ENSO signals in Figures 2.7
(Plate 1 ) and 2.8 (Plate 2 ) is dominated by the waxing and waning of a distinct
SO pattern, with a pronounced Indo-Pacific focus. The SO pattern is strongest
and most coherent in the LF ENSO sequence. Higher-latitude MSLP nodes
in the Pacific sector are a feature of both QB and LF ENSO signals. A
pronounced NAO signal is seen in the QB sequence of MSLP, but any
high-latitude AO response that might also be part of this pattern cannot be
discerned with the termination of data at 658 N (Hurrell et al. 2003 ). The LF
ENSO sequence contains a westwardly displaced North Atlantic MSLP feature
with perhaps some NAO signatures. Unfortunately, with the termination of the
data at 358 S, nothing can be said about high latitude Southern Hemisphere
phenomena such as the AAO or the Antarctic Circumpolar Wave (ACW)
(Simmonds 2003 ). Linkages between the ACW and ENSO are being explored.
Precipitation responses in the QB and LF ENSO sequences (Figures 2.7
(Plate 1 ) and 2.8 (Plate 2 ) ) reveal patterns indicative of those defined in
numerous studies. However, the sequences display much more information
about the evolution and extent of ENSO influences. While ''classical''
ENSO-induced precipitation impacts are seen over Australia, India, China,
Southern Africa, and North America in both sequences, there is evidence of a
more widespread influence on European climate, particularly in the QB
sequence. This European response has been seen previously in relationships
of global rainfall to phases of the SO (Stone et al. 1996 ), and in the specific
studies by Fraedrich et al.( 1992 ), and Mariotti et al.( 2002 ). Over eastern
China and Japan, the precipitation signal in both QB and LF ENSO sequences
shows more of a wider spatial response than is seen in ''classical'' studies. As
in Allan ( 2000 ), and other studies, the LF ENSO precipitation pattern also
resolves something of a moderate impact on West Africa, with implications
for Sahelian rainfall.
In line with the findings of White and Tourre ( 2003 ), the quasi-decadal
signal in MSLP and surface temperature (Figure 2.9 ( Plate 3 ) ) shows both
similarities and differences to the QB and LF ENSO structures (Figures 2.8
(Plate 2 ) and 2.9 (Plate 3 )). SST responses have more of a central to western
equatorial Pacific focus with strong links to higher latitudes along the west
coast of North America extending to Alaska on quasi-decadal time scales.
This Pacific pattern peaks during the mature stage of the quasi-decadal signal