Summer temperature in the eastern part of southern South America: its variability in the twentieth century and a teleconnection with Oceania
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The 1907–2001 summer-to-summer surface air temperature variability in the eastern part of southern South America (SSA, partly including Patagonia) is analysed. Based on records from instruments located next to the Atlantic Ocean (36°S–55°S), we define indices for the interannual and interdecadal timescales. The main interdecadal mode reflects the late-1970s cold-to-warm climate shift in the region and a warm-to-cold transition during early 1930s. Although it has been in phase with the Pacific Decadal Oscillation (PDO) index since the 1960s, they diverged in the preceding decades. The main interannual variability index exhibits high spectral power at ~3.4 years and is representative of temperature variability in a broad area in the southern half of the continent. Eleven-years running correlation coefficients between this index and December-to-February (DJF) Niño3.4 show significant decadal fluctuations, out-of-phase with the running correlation with a DJF index of the Southern Annular Mode. The main interannual variability index is associated with a barotropic wavetrain-like pattern extending over the South Pacific from Oceania to SSA. During warm (cold) summers in SSA, significant anticyclonic (cyclonic) anomalies tend to predominate over eastern Australia, to the north of the Ross Sea, and to the east of SSA, whereas anomalous cyclonic (anticyclonic) circulation is observed over New Zealand and west of SSA. This teleconnection links warm (cold) SSA anomalies with dry (wet) summers in eastern Australia. The covariability seems to be influenced by the characteristics of tropical forcing; indeed, a disruption has been observed since late 1970s, presumably due to the PDO warm phase.
KeywordsInterannual variability Interdecadal variability South America Patagonia Oceania Teleconnection
The authors would like to thank the availability of the Niño3.4 index (http://www.cgd.ucar.edu/cas/catalog/climind/TNI_N34/index.html#Sec5), the PDO index (http://jisao.washington.edu/pdo/PDO.latest), the IPO index (http://www.iges.org/c20c/IPO_v2.doc), the Zhang DJF AAO index (http://adrem.org.cn/Faculty/GongDY/docu/AAOsince1500.htm), and the Matlab code of the Rodionov’s sequential t test (http://www.beringclimate.noaa.gov). The SLP time series of Darwin (Australia) has been obtained from http://www.cgd.ucar.edu/cas/catalog/climind/darwin.ascii. SLP data from New Zealand have been accessed from http://cliflo.niwa.co.nz/ and Australian precipitation data from http://www.bom.gov.au/climate/data/. GHCN-Monthly version 2 provided by NOAA’s National Climatic Data Center (http://www.ncdc.noaa.gov/ghcnm/v2.php). Twentieth century reanalysis V2 data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, from their Web site (http://www.esrl.noaa.gov/psd/). ECMWF ERA-40 data used in this study have been obtained from the ECMWF Data Server (http://data-portal.ecmwf.int/). Thanks to Prof. Dr. Olivia Romppainen-Martius, Dr. Fabia Hüsler, Dr. Christoph Welker, Dr. Alexander Stickler, Dr. Renate Auchmann, Matthias Röthlisberger and Pablo Sánchez for their support during the preparation of the manuscript. This paper was greatly improved by the comments and suggestions of two anonymous reviewers. MJC acknowledges the BecasChile scholarship program (Comisión Nacional de Investigación Científica y Tecnológica de Chile, CONICYT).
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