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

Abstract

AbstractMonthly 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. Copyright © 2004 Royal Meteorological Society.