Middle-latitude climates - The Global Climate System: Patterns, Processes, and Teleconnections - page 118

autumn. Opposite correlations also occur with New Zealand temperature in
summer. Regional meridional flows tend to be more important, reflecting loca-
tional shifts in the ridges and troughs associated with the Rossby waves.

4.6.4 Correlations and spatial distributions
Fauchereau et al.( 2003 ) used NCAR/NCEP reanalysis (see Section 4.3 )to
reproduce sea level pressure distributions, geopotential height variations, and
wind flows (at 925 hPa) for the SH mid-latitudes between 1950 and 1999. The
authors were able to establish where spatially the strongest in-phase correlations
existed. Figure 4.8 presents a summary of the overall pressure results. The
strongest correlations occur between pressure fields in the SW Indian and SW
Atlantic Oceans, especially in the summer season. The Tasman Sea area between
Australia and New Zealand can also be included, but this has a considerably
weaker correlation with the other two. Figure 4.8 shows that there are no other
areas showing correlations across the mid-latitude zone.
Composite analysis in summer was then used to establish the changes in
spatial distribution of the pressure field under anomalous conditions. When
either warm anomalies occur in the SW parts of the Atlantic and Indian
Oceans, or cool anomalies occur in the NE, there is an associated shift of the
subtropical highs to the SE, and they become stronger. Significant anomalies
also appear in the Tasman Sea and in the southern Pacific, around 1208W. These
positive pressure anomalies can extend to 250 hPa over the Indian Ocean and
Tasman Sea, and to 400 hPa over the SE Pacific and the Atlantic. Fauchereau
et al.( 2003 ) state that, because these centers of composite correlation are distinct
from each other, and well separated, as well as being almost barotropic in nature,
a wave structure associated with the CPV is directly involved. These mid-
latitude variations are out of phase with the climatology of changes in geo-
potential heights over the subtropical and Antarctic regions (Goodwin et al. 2003 ).

(a)

Figure 4.8 Correlations
between MSLP pressures in
the southwest Indian Ocean
(a), southwest Atlantic
Ocean (b) and SST
anomalies for summer.
(After Fauchereau et al.
2003 , Figure 5, Copyright
John Wiley & Sons Ltd., with
permission)

EQ
5 S
10 S
15 S
20 S
25 S
30 S
35 S
40 S
45 S
50 S

-0.2

-0.3

0.2

-0.2

0.4

0.5

0.5

0.2

0.8
0. 0.3

-0.2

0.2

0.4

0.3

60 W 0 60 E 120 E 180 120 W

(b)

EQ
5 S
10 S
15 S
20 S
25 S
30 S
35 S
40 S
45 S
50 S

-0.2

-0.2

0.4

-0.2

0.2

0.6
0.3

0.8
0.6 0.7

0.3

60 W 0 60 E 120 E 180 120 W