M. Vuille et al., Climate variability in the Andes of Ecuador and its relation to tropical Pacific and Atlantic sea surface temperature anomalies, J CLIMATE, 13(14), 2000, pp. 2520-2535
The main spatiotemporal modes of seasonal precipitation and temperature var
iability in the Andes of Ecuador (1 degrees N-4 degrees S) and their relati
on to tropical Pacific and Atlantic sea surface temperature anomalies (SSTA
s) between 1963-92 are identified based on rotated principal component anal
ysis and cross-correlation techniques. Outgoing longwave radiation composit
es are analyzed during periods of strong oceanic forcing to confirm the pro
posed physical mechanisms. Despite the close proximity to the Pacific, prec
ipitation variability in the Andes of Ecuador is not related to SSTA in the
tropical Pacific domain alone. The El Nino-Southern Oscillation influence
is most dominant in the northwestern parr of the Andes during December-Febr
uary (DJF) and in the eastern Cordillera during June-August (JJA) and in bo
th cases associated with below- (above-) average precipitation during El Ni
no (La Nina) years. During most of the year precipitation variability over
the eastern Andes is related to a dipolelike correlation structure in the t
ropical Atlantic. featuring positive correlations with SSTA to the south of
the ITCZ and negative correlations to the north. The proposed mechanism in
volves positive SSTA in the tropical South Atlantic and contemporaneous neg
ative SSTA in the tropical North Atlantic, resulting in increased rainfall
over the eastern Cordillera. The only region with slightly increased precip
itation during El Nino events is confined to a narrow area along the wester
n Andean slope between 1 degrees and 3 degrees S in close proximity to the
Pacific. However, this relationship is weak. and only apparent in DJF Tempe
rature variability in the Andes can largely be explained by SSTA in the tro
pical Pacific domain. The temperature response closely follows SSTA in the
Nino-3 and Nino-3.4 regions with approximately one-month lag. The northernm
ost part of the Andes (north of 0.5 degrees N) is the only region where tem
peratures are significantly correlated with tropical North Atlantic SSTA.