La Niña events before and after 1979 and their impact in southeastern South America during austral summer: role of the Indian Ocean

Anomalous seasonal patterns of precipitation variability over South America (SA) associated with El Niño‐Southern Oscillation (ENSO) and non‐ENSO (residual) conditions were assessed during 1951–2016. Patterns were obtained from empirical orthogonal functions analysis of total and residual precipitation seasonal anomalies. In austral spring and summer, precipitation variability is dominated by a dipolar anomaly mode with a centre extending from northwestern to northeastern SA and another in central‐eastern Brazil and part of southeastern SA (SESA) during spring, and a centre in northwestern SA and another extending from northeastern SA to central and eastern Brazil and central SESA, during summer. These modes are associated with ENSO to a greater extent during spring than summer. In summer, there is a strong association of the dipolar precipitation pattern with sea surface temperature (SST) anomalies on the east coast of Brazil, which indicates local influence. In austral fall, SST anomalies in the tropical South Atlantic relate to precipitation anomalies in northeast SA, and those in the tropical north Atlantic (TNA) to precipitation anomalies in northwestern SA, through the intertropical convergence zone anomalous position modulated by SST anomalies. In this same condition, the ENSO acts only to intensify or weaken the dominant precipitation pattern, depending on its phase, mainly over SESA. In contrast, the second variability mode in fall is characterized by positive SST anomalies in the Indian Ocean and equatorial and southern Atlantic Ocean and negative in the TNA. The importance of ENSO and the Indian Ocean in the characterization of the SST dipole in the tropical Atlantic explains the main changes in precipitation patterns over northeastern Brazil not been discussed in previous studies.

Section: Introductionmentioning

confidence: 99%

Seasonal precipitation variability modes over South America associated to El Niño‐Southern Oscillation (ENSO) and non‐ENSO components during the 1951–2016 period

Souza

Andreoli

Kayano

et al. 2021

“…(2009) show that rainfall correlation with ENSO was not significant until 1977. Cazes‐Boezio and Talento (2016) identified a similar change for summertime rainfall over SESA: the correlation between the Niño3.4 index and rainfall resulted significant for 1979–2009 but not for 1949–1978, and they associate this change to a different behaviour of the Indian Ocean during La Niña events.…”

Section: Introductionmentioning

confidence: 84%

“…Scatterplots were constructed between rainfall in ZN/ZS and Niño3.4 index for subperiods P1 and P2, indicating ENSO events. Warm (El Niño) and cold (La Niña) ENSO events are defined based on Cazes‐Boezio and Talento (2016), that is, we consider El Niño (La Niña) years if the Niño3.4 index is larger (smaller) than 0.7°C (−0.7°C) and neutral years the ones with Niño3.4 values between −0.7 and 0.7°C.…”

Section: Methodsmentioning

confidence: 99%

A late 1980s shift in El Niño influence on rainfall over Uruguay during austral spring

Fernández¹,

Barreiro

2022

“…Their results provided evidence that the variability of the Indian Ocean SST can modulate the precipitation in SA during the austral autumn through remote mechanisms. In another study, Cazes‐Boezio and Talento (2016) analysed the teleconnections associated with ENSO before and after 1980. They concluded that after 1979 the events were accompanied by high temperatures in the Atlantic and Indian Oceans.…”

Section: Introductionmentioning

confidence: 99%

“…In addition, similarly to ENSO, recent studies highlight the role of the Indian Ocean in the climate of SA (Cazes-Boezio & Talento, 2016;de Souza et al, 2021;Kayano et al, 2021aKayano et al, , 2021bKayano et al, , 2021cTaschetto & Ambrizzi, 2012). Taschetto and Ambrizzi (2012) investigated the atmospheric response to the tropical Indian Ocean basin warming and its impact on the precipitation in SA when it was associated with or independent of ENSO.…”

Section: Introductionmentioning

confidence: 99%

Interdecadal Pacific Oscillation modulation of ENSO teleconnections in its decaying stages: Relations with Indian Ocean basin‐wide mode and South American precipitation

Souza

Andreoli

Kayano

et al. 2023

This study examines the Interdecadal Pacific Oscillation (IPO) modulation of the El Niño-Southern Oscillation (ENSO) teleconnections in its decaying stages with the tropical ocean by focusing on the Indian Ocean Basin-Wide (IOBW) mode and the precipitation over South America (SA) in the 1901-2012 period. Composite analyses revealed that the ENSO teleconnections are IPO-modulated due to the differential ENSO decaying speed, which is slower during the positive than negative IPO phase, for both El Niño (EN) and La Niña (LN) cases. Negative precipitation anomalies related to EN persist over northeastern SA until austral winter for the positive IPO phase (POS IPO), while significant opposite sign anomalies occur in this region for the negative IPO phase (NEG IPO). These results are associated with the Walker circulation's reversal during NEG IPO which is, in turn, accompanied by negative IOBW. During the POS IPO, the positive IOBW causes upward movements over there and, by continuity, downward movements over SA. In the NEG IPO, for LN events the wave train originating in the north of Australia propagates toward subtropical SA, which, coupled with the surface circulation, causes dryness in this region. In addition, the rapid decay of LN in the NEG IPO, followed by the emergence of EN, caused changes in the Walker circulation, such that enhanced upward movements occurred over the Pacific and SA region, and downward movements over the Indian Ocean until austral winter. In turn, the slower decay of the LN in the POS IPO maintains strong subsidence over the central Pacific and weak upward motions over western SA. So, the EN (LN) and positive (negative) IOBW during the POS (NEG) IPO prolong the scarcity of precipitation over equatorial (subtropical) SA. Persistent dry periods over these regions during the ENSO decaying stage might have important implications for the seasonal forecasts.