Effects of El Niño–southern oscillation on southernmost South America precipitation at 53 °S revealed from NCEP–NCAR reanalyses and weather station data

Abstract

Monthly mean records of climate data over southern South America from the National Centers for Environmental Prediction (NCEP)-National Center for Atmospheric Research (NCAR) reanalysis project (NNR) were processed to determine possible teleconnections of El Niño-southern oscillation with precipitation at 53°S in the southernmost Andes. The NNR data used include precipitation rate, zonal wind speed and sea-level pressure (SLP). All data were correlated to the southern oscillation index (SOI) allowing for time leads/time lags of up to 8 months.Significant positive correlation at the 99% level between SOI and SLP is obtained north of 40°S (r = 0.4). SLP south of 58°S negatively correlates with SOI (r = −0.3). In consequence, during El Niño events the SLP gradient over Patagonia decreases, leading to lower wind speeds. Precipitation on the west coast of Patagonia depends greatly on the strength of the west winds due to orographically induced precipitation. According to this, positive correlation (r = 0.4) between SOI and precipitation rate anomalies is found west of the Patagonian coastline between 45 and 55°S based on annually averaged data. Precipitation decreases by about 15% during strong El Niños. The correlation decreases to insignificant values east of the Andes mountain range. Correlation between SLP gradient and SOI along the west coast of southern Patagonia is largest from austral spring to summer in year 0 of an El Niño event and in April of year +1. Correlations are particularly strong at a time lag of +1 and +2 months, with SOI leading the SLP gradient. Correlation was found to vary in time, with weak correlations during the 1970s and early 1980s and enhancing teleconnection towards the turn of the century. The generally weak positive correlation between precipitation and SOI was also found by comparing precipitation data from weather stations at 53°S on the west coast of South America with SOI.

Spatio‐temporal rainfall patterns in Southern South America

“…Quintana (2004) excluded this record from his analysis citing inadequate expertise of the personnel collecting the data. Schneider and Gies (2004), however, validated this record using reanalysis data. The lack of correlation of these data with other records in the vicinity prevents conventional homogeneity analysis.…”

“…The most extreme contrast is between Guarello (7220 mm/year) and Lago Argentino (209 mm/year, ca 200 km east) at ca 49°S. The high precipitation at this latitude reflects the position of the most frequent cyclone tracks within the west wind zone (Schneider and Gies, 2004;Garreaud and Falvey, 2008). Stations in the eastern foothills of the Cordillera (Bariloche, Esquel, Balmaceda, Lago Argentino and Punta Arenas) show a marked decrease in rainfall due to the rain shadow (Figure 2).…”

“…Recently, Pezoa (2003), Quintana (2004) and Schneider and Gies (2004) have studied the spatial and temporal variability of annual, seasonal and monthly precipitation records from Chilean stations on the west coast of SSAm. Pezoa (2003) used PCA to study the spatial patterns of precipitation from 57 Chilean stations between 33 and 53°S between 1931 and 2001.…”

“…He also pointed out the significant role of the Antarctic Oscillation (AAO) and its regional counterpart that he called the Antarctic-Pacific Oscillation (AAPO), on rainfall variability in Southern Chile (Quintana, 2004). Schneider and Gies (2004) used precipitation rate, zonal wind speed and sea level pressure data from the NCEP-NCAR (National Center for Environmental Prediction-National Center for Atmospheric Research) reanalysis data to investigate the influence of El Niño events on precipitation south of 40°S. They show clear evidence that a blocking effect in high latitudes of the South Pacific over the area of the Bellingshausen Sea is connected with the precipitation variability of southernmost Chile.…”

A promising location in Patagonia for paleoclimate and paleoenvironmental reconstructions revealed by a shallow firn core from Monte San Valentín (Northern Patagonia Icefield, Chile)

“…However, considering the first half of the 1990s, when SOI is consistently negative, we find some high deuterium excess and low d 18 O values that could be consistent with warmer oceanic sources and colder local temperatures (m 1990 -1995 = À18.13%, s = 1.80). Even though ENSO probably has an insignificant impact on temperature at this latitude [Rosenbluth et al, 1997;Garreaud et al, 2008], it is well known that positive phase of ENSO reduces precipitation by about 15%, over the west coast of Patagonia [Allan and D'Arrigo, 1999;Schneider and Gies, 2004] due to decreased westerly circulation. Precisely, it has been shown that the rainfall deficit occurs during summer (JFM) when El Niño attains its maximum.…”