Dendroclimatology from Regional to Continental Scales: Understanding Regional Processes to Reconstruct Large-Scale Climatic Variations Across theWestern Americas - Dendroclimatology - page 179

Fig. 7.2 Correlation coefficients between annual-averaged sea surface temperatures and ( upper )
Cold Tongue (CT) index (1903-1990) and ( lower ) Global Residual (GR) index (1903-1990). The
contour interval is 0.2, dashed where negative. Correlations greater than +0.2, or less than -0.2,
pass a two-tail Student's t -test of being different from zero at 95% significance levels (modified
from Dettinger et al. 2001 )
1997 ; Garreaud and Battisti 1999 ; Deser et al. 2004 ) . The physical processes
responsible for the decadal variability across the Pacific remain uncertain, but are
connected to well-documented pan-Pacific changes in the atmosphere and ocean
in recent decades. For example, the 1976-1977 climatic shift influenced climatic
conditions all along the western Americas and is a remarkable manifestation of
this Pacific decade-scale climatic variability (Ebbesmeyer et al. 1991 ) . Sea surface
temperatures along the equatorial belt and along the coast of the Americas become
warmer, while further west at temperate latitudes the sea surface becomes cooler
(Fig. 7.2 ) . The array of atmospheric and oceanic changes that have been linked
to these basin-wide regime shifts is collectively referred to as the Pacific Decadal
Oscillation or the Pacific Interdecadal Mode (Mantua et al. 1997 ; Enfield and
Mestas-Nuñez 2000 ) . Warm and wet decades in the equatorial Pacific tend to be
marked by extratropical circulation patterns that bring mild weather conditions to
coastal Alaska and northern Patagonia. In contrast to the interannual mode of ENSO
variability, the decadal mode is characterized by less pronounced anomalies in the