The role of the Atlantic Multidecadal Oscillation precondition in the teleconnection of different El Niño‐Southern Oscillation types and impacts on the 15°N–15°S South American sector precipitation

Abstract

The Eastern Pacific (EP) and Central Pacific (CP) El Niño‐Southern Oscillation (ENSO) types and their impacts on the tropical North Atlantic (TNA) SST variability and 15°N–15°S South American precipitation during the warm and cold phases of the Atlantic Multidecadal Oscillation (WAMO and CAMO) were evaluated during the 1901–2012 period. The results show more frequent ENSO events during the CAMO. The El Niño (EN) (La Niña [LN]) events, regardless of type (EP or CP), during the WAMO (CAMO) were accompanied by a warming (cooling) in the TNA after its mature phases. In these cases, extratropical teleconnection patterns are established through variations in the Pacific/North America (PNA) teleconnection pattern and are accompanied by variations in the Walker circulation. For the EN (LN) in the CAMO (WAMO), the tropical teleconnections occur predominant, through the Walker cell and the zonal inter‐basin gradient, which is intensified due to the SST gradient between the eastern equatorial Pacific (non‐neutral anomalies) and the equatorial Atlantic (neutral anomalies). These circulation pattern changes affect the precipitation patterns in the 15°N–15°S South American sector during December–January–February (D(0)JF(+1)) and March–April–May (MAM(+1)). The EP EN (EPEN) events are associated with the intensification of the negative precipitation anomalies in northeastern Brazil (NEB) during the WAMO and in the central part of the Amazon during the CAMO. In the case of CP EN (CPEN) events, the greatest differences between the AMO phases occur during MAM(+1), with reverse sign anomalies over northwestern South America. In the case of LN events, the largest differences occur in NEB, with reduced rainfall in the WAMO, regardless of type EP or CP. The results presented here highlight the role of low frequency oscillations in defining the teleconnection patterns between tropical Pacific and Atlantic Oceans, not discussed previously.

Multiyear La Niña effects on the precipitation in South America

“…However, according to Wu et al (2019), a strong EN before an LN induces warming in the tropical Atlantic and Indian Oceans, delaying the adjustment of these oceans to the LN cooling; and the warming in the tropical Atlantic intensifies the interbasin gradient between this ocean and the eastern tropical Pacific. Since the ENSO teleconnection in the tropical Atlantic is a determinant of the precipitation variability in northeastern Brazil (Andreoli and Kayano, 2006;Figliuolo et al, 2020), the multiyear LN events preceded or not by EN might lead to distinct teleconnection over SA. Here we documented the physical mechanisms associated with a multiyear LN during its Y1 and Y2, which cause distinct seasonal precipitation anomaly patterns in SA.…”

Impacts of teleconnection patterns on South America climate

“…Kayano and Capistrano 119 show that El Niño (La Niña) events are stronger during the cold (warm) phase of the AMO due to the anomalous Walker cell to be reinforced by El Niño (La Niña), as a consequence of the negative (positive) SST gradient between the eastern equatorial Pacific and the equatorial Atlantic. According to Figliuolo et al, 120 the anomalous Walker cell shows sinking (ascending) motions and increased (decreased) sealevel pressure in the equatorial and southern parts of the tropical Atlantic, increasing the Pacific-Atlantic inter-basin zonal SST gradient during El Niño and the cold phase of the AMO. Figliuolo et al 120 also evaluated the concomitant impact of the different ENSO (Eastern Pacific and Modoki El Niño and La Niña) episodes and the AMO (warm and cold) on South American precipitation; some of their results include: (1) Eastern Pacific El Niño (canonical events) and the warm phase of the AMO are associated with the intensification of negative precipitation anomalies in northeastern Brazil, since the ITCZ is northward of its position; (2) Eastern Pacific El Niño and the cold phase of the AMO are associated with the intensification of negative precipitation anomalies in the central part of the Amazon caused by the anomalous sinking branch of the Walker cell; (C) Modoki El Niño show a more variable signal (see Figliuolo et al 120 for more details); and (4) Eastern Pacific and Modoki La Niña events, together with the warm phase of the AMO, contribute to negative anomalies in northeastern Brazil.…”

Interdecadal variability of the austral summer precipitation over the Central Andes

“…The AMO also modulates precipitation over South America and its teleconnections with ENSO (Kayano and Capistrano, 2014;Flantua et al, 2016;Grimm et al, 2016;Barichivich et al, 2018;Figliuolo et al, 2020). Flantua et al (2016) found a negative correlation between AMO and annual precipitation in the western Cordillera of the southern Peruvian Andes.…”

“…The two phases of the AMO result in different patterns of austral summer precipitation anomalies, depending on the phases of the central and eastern ENSO indices between 15 °N and 15 °S (Figliuolo et al, 2020). For example, the eastern Pacific El Niño enhances (reduces) DJF precipitation over the central Peruvian Andes during the warm (cold) AMO phase.…”