资源环境科技发展态势分析平台

The Pacific Interdecadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO) influence in different ways the La Nina (LN) related teleconnections in South America. The low-frequency backgrounds in the Atlantic and Pacific Oceans play an important role in modulating the LN-related Walker and Hadley cells and the Rossby wavetrain pattern in the Southern Hemisphere. The illustration shows the LN-related SST anomaly pattern during the austral summer for distinct low-frequency backgrounds. This analysis investigates the concomitant influence of two dominant low-frequency modes, the Pacific Interdecadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO), on the La Nina (LN) related climate teleconnections over South America (SA). Four possible low-frequency backgrounds are analysed: WAMO/WPDO, WAMO/CPDO, CAMO/WPDO and CAMO/CPDO, with the letters W and C referring, respectively, to the warm and cold phases of the AMO and PDO. The low-frequency anomalous sea surface cooling (warming) in the tropical Pacific during the CPDO (WPDO) favours (impedes) the settling of the LN-related negative SST anomalies in this oceanic sector. Thus, the LN-related SST anomaly patterns in the tropical Pacific in the CPDO backgrounds are meridionally more extensive and stronger than those in the WPDO backgrounds. The highest and lowest percentages of the years that experienced LN events occurred during the WAMO/CPDO and CAMO/WPDO backgrounds, respectively. The northern node of the LN-related wet-dry dipole between northern SA and southeastern SA (SESA) occurs in most seasons for all backgrounds. However, the southern node occurs in specific seasons: spring and summer for the WAMO/WPDO, winter and spring for the WAMO/CPDO, winter and summer for the CAMO/WPDO and spring for the CAMO/CPDO. Also, the LN effect on the South American monsoon with a wet-dry dipole between northern SA and eastern Brazil during summer is noted in most backgrounds, but with differences among them. We discuss here the differences in the precipitation anomaly patterns, Walker and Hadley cells and Rossby wavetrain patterns among the backgrounds. The low-frequency Atlantic and Pacific backgrounds play an important role in defining the rainfall anomaly pattern associated with the LN. The results shown here have not been discussed before and might be useful mainly for climate monitoring purposes.