Section 6.4: Characteristic Features
107
stronger than expected by chance would require a field significance test on the
extratropical correlations (see Chapter 9; field significance examples are given
in Section 6.5.3). In the North Pacific, there are negative correlations with
sea-Ievel pressure, and on the western flank of this region there are significant
correlations with anomalous northerly wind, consistent with the geostrophic
wind relation. In the Atlantic, positive sea~level pressure correlations at
65° N and negative correlations near 35° N are geostrophically consistent with
the correlations with easterly wind anomalies 'over 40 - 60° N. The remote
tropical and extratropical teleconnections with SST p2 may in the main
be conditional on EI Nifio and La Nifia events modulating convection in
the western Pacific, and triggering the anomalous meridional overturning
from Indonesia to the China Sea. The associated strong diabatic heating
anomalies in this region may modulate the tropic-wide circulation, and lead
to some of the extra-tropical connections in the process. It is also possible
that the connection between warm events (cold events) in the Pacific ancl
near-surface divergence (convergence) in the tropical Atlantic results from a
direct divergent zonal overturning of the atmosphere from the east Pacific to
the Atlantic (J anicot et al., 1994).
6.4.3 Patterns in the Marine Atmosphere Associated
with EOF p3
The time coefficients of SST p3 in recent decades mainly describe a long period elimate fluctuation (Figure 6.1b). The correlations with SST p3 (Figure
6.3) should be viewed as descriptive of the atmospheric changes that have
accompanied the low frequency SST change. The strongest tropical atmospheric change is in the Atlantic, though changes in the Indian and Pacific
Ocean are evident too. In the Atlantic, the correlations suggest that a cooler
Northern Hemisphere has accompanied higher sea-Ievel pressure and anomalous near-surface divergence in the North Atlantic, lower sea-Ievel pressure
and anomalous near-surface convergence elose to Brazil, and connecting nearsurface wind anomalies all with a northerly component from 20° S to 20° N,
west of 10° W. This wind pattern may in part be a response to the SST
changes, and may in part be maintaining the SST changes, since the wind
anomaly is likely to have modified the cross-equatorial ocean current and
the associated ocean heat fluxes that are important for the relative temperature of the North Atlantic and South Atlantic (some early ideas are found
in Bjerknes, 1964).
In the northeastern Pacific, the correlations suggest that the cooler Northern Hemisphere accompanied anomalous northerlies near 10° N with anomalous near-surface divergence. In the Indian Ocean, there is evidence for a
reduced strength of the Indian monsoon, with higher sea-Ievel pressure in the
northwestern Indian Ocean, and reduced southwesterly flow (i.e. anomalous
northeasterly) near 15° N in the Arabian Sea. It is also known that rainfall in
India showed some reduction in the later period, and that the African conti-
107
stronger than expected by chance would require a field significance test on the
extratropical correlations (see Chapter 9; field significance examples are given
in Section 6.5.3). In the North Pacific, there are negative correlations with
sea-Ievel pressure, and on the western flank of this region there are significant
correlations with anomalous northerly wind, consistent with the geostrophic
wind relation. In the Atlantic, positive sea~level pressure correlations at
65° N and negative correlations near 35° N are geostrophically consistent with
the correlations with easterly wind anomalies 'over 40 - 60° N. The remote
tropical and extratropical teleconnections with SST p2 may in the main
be conditional on EI Nifio and La Nifia events modulating convection in
the western Pacific, and triggering the anomalous meridional overturning
from Indonesia to the China Sea. The associated strong diabatic heating
anomalies in this region may modulate the tropic-wide circulation, and lead
to some of the extra-tropical connections in the process. It is also possible
that the connection between warm events (cold events) in the Pacific ancl
near-surface divergence (convergence) in the tropical Atlantic results from a
direct divergent zonal overturning of the atmosphere from the east Pacific to
the Atlantic (J anicot et al., 1994).
6.4.3 Patterns in the Marine Atmosphere Associated
with EOF p3
The time coefficients of SST p3 in recent decades mainly describe a long period elimate fluctuation (Figure 6.1b). The correlations with SST p3 (Figure
6.3) should be viewed as descriptive of the atmospheric changes that have
accompanied the low frequency SST change. The strongest tropical atmospheric change is in the Atlantic, though changes in the Indian and Pacific
Ocean are evident too. In the Atlantic, the correlations suggest that a cooler
Northern Hemisphere has accompanied higher sea-Ievel pressure and anomalous near-surface divergence in the North Atlantic, lower sea-Ievel pressure
and anomalous near-surface convergence elose to Brazil, and connecting nearsurface wind anomalies all with a northerly component from 20° S to 20° N,
west of 10° W. This wind pattern may in part be a response to the SST
changes, and may in part be maintaining the SST changes, since the wind
anomaly is likely to have modified the cross-equatorial ocean current and
the associated ocean heat fluxes that are important for the relative temperature of the North Atlantic and South Atlantic (some early ideas are found
in Bjerknes, 1964).
In the northeastern Pacific, the correlations suggest that the cooler Northern Hemisphere accompanied anomalous northerlies near 10° N with anomalous near-surface divergence. In the Indian Ocean, there is evidence for a
reduced strength of the Indian monsoon, with higher sea-Ievel pressure in the
northwestern Indian Ocean, and reduced southwesterly flow (i.e. anomalous
northeasterly) near 15° N in the Arabian Sea. It is also known that rainfall in
India showed some reduction in the later period, and that the African conti-