资源环境科技发展态势分析平台

The dominant seasonal surface air temperature (SAT) anomalous modes over entire South America (SA) for the 1951-2010 period were investigated. The El Nino-Southern Oscillation (ENSO) and non-ENSO (residual - RES) characteristics of the SAT anomalous modes and the associated precipitation and temperature advection anomalies were discussed. The SAT (referred to as TOT) and RES modes were obtained from the empirical orthogonal function analyses, and the ENSO modes from the correlation analyses between the SAT anomalies and the Oceanic Nioo index. The SAT TOT modes are in general, weakly linked to the ENSO, except for the first summer and the fourth spring TOT modes. For these two modes, the precipitation variations are more crucial than the temperature advection variations in defining the SAT anomaly patterns. On the other hand, the first winter and autumn TOT modes contain mostly the non-ENSO components and feature an extensive warmed area in tropical and subtropical SA. For these modes, the subtropical warming is due to the temperature advection. The TOT modes with a weak relation to the ENSO and the corresponding RES modes show a dipolar pattern with a warm node in tropical SA and the cold one in extratropical SA, and is determined mostly by the precipitation. Nevertheless, the cold advection reinforces the cold node of the winter and summer modes. In some cases, the regional systems contribute to the SAT anomalies. The South American low-level jet contributes to the positive SAT anomalies in central and eastern Brazil for the second winter and first spring RES modes and the South Atlantic Convergence Zone influences the first summer RES mode. The SAT modes describe mostly the interannual variations of the SAT patterns over SA, but some of them also contain decadal and multidecadal time scale variations.