Influence of the Indian Ocean Dipole on the Large-Scale Circulation in South America

Abstract

The influence of each phase of the Indian Ocean Dipole (IOD) on the largescale circulation in South America is investigated using rainfall observations, fully-coupled, large-ensemble, historical simulations (LENS), and forced experiments using the coupled model’s atmospheric component. IOD events often occur when El Niño Southern Oscillation (ENSO), the largest source of interannual variability of precipitation in South America, is active. To distinguish from effects of ENSO, only cases during neutral ENSO conditions are analyzed in LENS and observations. During the positive IOD polarity, a perturbation in the localWalker circulation leads to increased convection over equatorial South America, resulting in wet anomalies in the Amazon basin. This signal is the opposite of what is expected during El Niño events. Tropical convection anomalies in the Indian Ocean also force an extratropical Rossby wave train that reaches subtropical South America. During positive IOD, the moisture flux from the Amazon to central and southeastern Brazil weakens, resulting in a drying of the area associated with the South Atlantic Convergence Zone. Meanwhile, the South Atlantic Subtropical High strengthens, contributing to a drying in southeastern Brazil. During negative IOD, the induced wave train from the Indian Ocean leads to increased moisture transport to the La Plata basin, leading to wet anomalies in the region.

The Role of the Subtropical and Extratropical Southern Hemisphere Anomalous Sea Surface Temperature in the Trans‐Seasonal Influence of Southern Annular Mode on Rainfall Over Southeastern South America

“…The wave train is associated with the strengthened Atlantic subtropical high in the SESA region, which inhibits the southward transport of moisture from the Amazon basin, resulting in dry conditions during the positive phase of IOD. The suggested mechanism was further verified by large-ensemble simulations and numerical experiments (Sena & Magnusdottir, 2021). On the other hand, studies have related the rainfall variability to the regional forcing associated with the South American low-level jet (SALLJ), the South Atlantic convergence zone (SACZ) and sea surface temperature (SST) variations in the tropical Atlantic (Cerón et al, 2021;Diaz et al, 1998;Fernandes & Rodrigues, 2018;Montini et al, 2019).…”

“…For example, the influence of ENSO can be achieved through an increase in the northerly transport of moisture in surface levels and the advection of cyclonic vorticity in higher levels, leading to the moisture abundance associated with the wet conditions in the study region during El Niño (Grimm, 2011; Grimm et al., 2000; Martín‐Gómez & Barreiro, 2016; Silvestri, 2004). The IOD can excite the eastward‐oriented Rossby waves from the Indian Ocean to South America, where the study region is located (Chan et al., 2008; Martín‐Gómez & Barreiro, 2016; Sena & Magnusdottir, 2021). The wave train is associated with the strengthened Atlantic subtropical high in the SESA region, which inhibits the southward transport of moisture from the Amazon basin, resulting in dry conditions during the positive phase of IOD.…”

“…A bunch of previous studies indicate various atmospheric and oceanic phenomenon that influences the variability of rainfall in SESA in different timescales (Alvarez et al, 2014;Grimm & Ambrizzi, 2009;Grimm & Tedeschi, 2009;Liebmann et al, 1999;Seager et al, 2010;Sena & Magnusdottir, 2021;Silva et al, 2020;Silvestri, 2004). Such climatic phenomena are the Madden-Julian Oscillation in intra-seasonal timescales, Indian Ocean Dipole (IOD) and El Niño-Southern Oscillation (ENSO) in interannual timescales, Atlantic multidecadal oscillation and Pacific decadal oscillation in multidecadal timescales.…”

Literature survey of subseasonal‐to‐seasonal predictions in the southern hemisphere

“…Recent studies suggest that the Indian Ocean Dipole (IOD) plays an important role in predicting the ENSO in the tropical Pacific through teleconnections (Li et al, 2022;Liu et al, 2023). The positive IOD events are associated with reduced rainfall over western and southern Australia (Zhao et al, 2019), enhanced rainfall in eastern and southern Africa (Black et al, 2003), and reduced rainfall over central and southeastern Brazil and enhanced rainfall over the Amazon (Sena & Magnusdottir, 2021). Furthermore, ENSO can modulate the Madden Julian Oscillation (MJO) through teleconnection (e.g., Lee et al, 2019;Wei & Ren, 2019;Fernandes & Grimm, 2023).…”

Effect of the Quasi‐Biennial Oscillation on the Madden Julian Oscillation Teleconnections in the Southern Hemisphere

“…(2018) estimate that about a quarter of the MJO‐related perturbations in Amazon rainfall may be related to extratropical influences. The extratropical wave train is relevant to the precipitation over the subtropical and extratropical South America (e.g., Sena & Magnusdottir, 2021, and references therein).…”