El Niño-Southern Oscillation and Indian Ocean Dipole Modes: Their Effects on South American Rainfall during Austral Spring

Mary T Kayano,Rodrigo A F Souza,Itamara P Souza,Wilmar L Cerón,Rita V Andreoli,Teresita Canchala

doi:10.3390/atmos12111437

Abstract

This paper examines the effects of the tropical Pacific Ocean (TPO) and Indian Ocean Dipole (IOD) modes in the interannual variations of austral spring rainfall over South America (SA). The TPO mode refers to the El Niño-Southern Oscillation (ENSO). The isolated effects between IOD and TPO were estimated, events were chosen from the residual TPO (R-TPO) or residual IOD (R-IOD), and the IOD (TPO) effects for the R-TPO (R-IOD) composites were removed from the variables. One relevant result was the nonlinear precipitation response to R-TPO and R-IOD. This feature was accentuated for the R-IOD composites. The positive R-IOD composite showed significant negative precipitation anomalies along equatorial SA east of 55° W and in subtropical western SA, and showed positive anomalies in northwestern SA and central Brazil. The negative R-IOD composite indicated significant positive precipitation anomalies in northwestern Amazon, central–eastern Brazil north of 20° S, and western subtropical SA, and negative anomalies were found in western SA south of 30° S. This nonlinearity was likely due to the distinct atmospheric circulation responses to the anomalous heating sources located in longitudinally distinct regions: the western tropical Indian Ocean and areas neighboring Indonesia. The results obtained in this study might be relevant for climate monitoring and modeling studies.

Highlights

It is well known that the El Niño-Southern Oscillation (ENSO) teleconnections strongly modulate the interannual rainfall variability over South America (SA) through an atmospheric bridge in the tropics via anomalous Walker and local Hadley cells [1], and in the subtropics and extratropics via Rossby wave train patterns [2,3]
The relationships between the Indian Ocean Dipole (IOD) and ENSO modes might occur in the inverse direction, with the IOD preceding the ENSO [32]. These results strongly suggest that the climate variability associated with IOD in several areas might contain the ENSO effects and vice versa
Interannual precipitation variations in SA during austral spring might be modulated by the ENSO [9,10,11] and IOD [25,27] modes

Summary

Introduction

It is well known that the El Niño-Southern Oscillation (ENSO) teleconnections strongly modulate the interannual rainfall variability over South America (SA) through an atmospheric bridge in the tropics via anomalous Walker and local Hadley cells [1], and in the subtropics and extratropics via Rossby wave train patterns [2,3]. The IOD shows weak anomalous warming in the western TIO and a cooling of off the coasts of Sumatra and Java Islands during its positive phase, and a reversed SST anomaly pattern during its negative phase [15] These modes present their largest variability in distinct seasons: the IOBW mode during austral summer and autumn [16,17] and the IOD mode during austral winter and spring [15,18]. The IOD mode affects the rainfall variability in eastern and southeastern SA during austral spring [25], when it has the maximum intensity [15,18] This relationship occurs through an atmospheric Rossby wave train pattern connecting the TIO and SA across the southern mid-latitude waveguide [25,26], with the positive IOD mode intensifying the South Atlantic subtropical high [25]. The analysis in this research is distinct from Chan et al.’s [25] and Sena and Magnusdottir’s [27]

Materials and Methods

Findings

Discussions and Conclusions