Geoscience Reference
In-Depth Information
For the common interval 1650-1980, the first PC of the El Asiento chronology in
year
t
and
t
+1 is significantly correlated with the Niño-3 index (
r
0.34,
p
< 0.01),
which may be considered as a first indication of persistence in the influence of trop-
ical SSTs on precipitation in central Chile. Long-term relationships between SST in
the tropical Pacific and precipitation in the Bolivian Altiplano are also inferred from
the statistically significant correlation between the two independent estimates (
r
=
=
−
0.34,
p
< 0.01).
7.3.2.2 Dominant Oscillations in Precipitation Variations
Cross-spectral analysis was used to identify coherent oscillation modes in tropical
Pacific SST and precipitation variations in central Chile and the Bolivian Altiplano.
Coherent oscillations between Niño-3 index and precipitation in central Chile are
observed at 3.5 years, the classic El Niño frequency domain, but also at 20-28 years,
spectral analysis of the Niño-3 index and
Polylepis
records in Bolivia indicates
significant coherence at 2.9, 3.2, 3.8, 8.5-10, and 19 years, a cycle also identified in
Following the previous cross-spectral analysis, we proceed to isolate the major
waveforms in the precipitation-sensitive records using singular spectrum analysis
modes of common variance at 3.6 and 28 years, were isolated from the Niño-3 and
and precipitation-sensitive chronologies in central Chile (
upper
) and the Bolivian Altiplano (
lower
)
during the interval 1650-1981. Records are highly coherent at 3-4 years, the classic El Niño
oscillations, but also at decennial-scale wavelengths longer than 10 years.
Horizontal broken lines
represent the 95% confidence level for the squared-coherency analyses. The periods are given in
years for each significant coherency peak
