Analysis of oceans' influence on spring time rainfall variability over Southeastern South America during the 20th century

Martín-Gómez, Verónica; Barreiro, Marcelo

doi:10.1002/joc.4428

Cited by 27 publications

(14 citation statements)

References 54 publications

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“…This result suggested that the atmospheric response associated with Canonical El Niño is highly linear. these two circulation anomalies induced a strong geopotential height gradient over SSA and favored advection of cyclonic vorticity over there (in agreement with References [2,17,32]). Comparing with Figure 3a, where the composite map of the Canonical El Niño events was plotted, it was possible to see that the distribution of the extratropical z200 anomalies was similar with both metrics.…”

Section: Canonical El Niñosupporting

confidence: 87%

“…Additionally, it was possible to see a short Rossby wave train excited in the central-tropical Pacific, around (35° S, 270° E), that propagated eastward inducing an anomalous anticyclonic circulation over northeastern SSA around (25° S, 310° E). As in the correlation map(Figure 2b), these circulation anomalies induced a strong geopotential height gradient over SSA and favored the advection of cyclonic vorticity(Figure 3a), in agreement with References[2,17,32].…”

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confidence: 83%

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Southern Hemisphere Sensitivity to ENSO Patterns and Intensities: Impacts over Subtropical South America

2020

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El Niño flavors influence Subtropical South American (SSA) rainfall through the generation of one or two quasi-stationary Rossby waves. However, it is not yet clear whether the induced wave trains depend on the El Niño pattern and/or its intensity. To investigate this, we performed different sensitivity experiments using an Atmospheric General Circulation Model (AGCM) which was forced considering separately the Canonical and the El Niño Modoki patterns with sea surface temperature (SST) maximum anomalies of 1 and 3 °C. Experiments with 3 °C show that the Canonical El Niño induces two Rossby wave trains, a large one emanating from the western subtropical Pacific and a shorter one initiated over the central-eastern subtropical South Pacific. Only the shorter wave plays a role in generating negative outgoing longwave radiation (OLR) anomalies over SSA. On the other hand, 3 °C El Niño Modoki experiments show the generation of a large Rossby wave train that emanates from the subtropical western south Pacific and reaches South America (SA), promoting the development of negative OLR anomalies over SSA. Experiments with 1 °C show no impacts on OLR anomalies over SSA associated with El Niño Modoki. However, for the Canonical El Niño case there is a statistically significant reduction of the OLR anomalies over SSA related to the intensification of the upper level jet stream over the region. Finally, our model results suggest that SSA is more sensitive to the Canonical El Niño, although this result may be model dependent.

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Section: Canonical El Niñosupporting

confidence: 87%

supporting

confidence: 83%

Southern Hemisphere Sensitivity to ENSO Patterns and Intensities: Impacts over Subtropical South America

2020

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“…For example, Barreiro (2010) reported that in Spring, about 50% of rainfall variability in SESA is explained by ENSO. Also, Martín‐Gómez and Barreiro (2016) found ENSO and the Indian Ocean Dipole influence rainfall in SESA during Spring through the interaction of a Rossby wave train induced by the Indian Ocean and another one forced by the tropical Pacific. There are fewer studies that relate rainfall anomalies in SESA with intraseasonal oscillations such as the Madden‐Julian Oscillation (Madden and Julian, 1994).…”

Section: Introductionmentioning

confidence: 99%

Influence of Madden–Julian Oscillation on extreme rainfall events in Spring in southern Uruguay

Ungerovich¹,

Barreiro

Masoller

2021

Intl Journal of Climatology

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The influence of Madden–Julian Oscillation (MJO) on the dynamics of extreme rainfall events during austral Spring in Uruguay is investigated. The research is focused on the southern region of the country, which includes 15 weather stations. Extreme events are defined as days in which accumulated rainfall exceeds the 90 percentile of rainy days, and MJO is classified according to the Real‐time Multivariate MJO series 1 (RMM1) and 2 (RMM2) indices. Given that the extratropical teleconnections associated with MJO take at least 1 week to set up, we explore the influence of MJO up to 11 days prior to extreme events. A nonlinear time series analysis is performed (using symbolic patterns known as ordinal patterns) in order to consider the effects of the persistence of particular phases of MJO on the dynamic of extreme rainfall events. We find that MJO has the highest influence on extreme rainfall events in the region when it shows a persistence in phases 4 and 5 for more than 5 days, which intensifies the polar jet, influencing the trajectories of the transient waves that propagate in high latitudes, favouring geopotential disturbances over Uruguay. In other cases, the atmospheric pattern that leads to extreme rainfall events is characterized by a blocking episode that prevents transient activity from high latitudes to reach Uruguay, and the disturbances associated with the extreme events propagate along the subtropics.

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“…Surface momentum and energy fluxes are defined by bulk aerodynamic formulas with different exchange coefficients between land and sea (chapter 4, Hartmann, 1994). A more detail description of all these parametrization schemes can be found on https://www.ictp.it/research/esp/models/speedy.aspx . Finally, this model has been previously used to investigate impacts of ENSO on South America (e.g., Barreiro and Díaz, 2011; Martín‐Gómez and Barreiro, 2015).…”

Section: Methodsmentioning

confidence: 99%

Southern hemisphere circulation anomalies and impacts over subtropical South America due to different El Niño flavours

Martín-Gómez

Barreiro

Losada

et al. 2020

Intl Journal of Climatology

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El Niño–Southern Oscillation (ENSO) exhibits different flavours with worldwide impacts. However, the associated teleconnections with subtropical South America (SSA) are still controversial and modelling studies are needed. Here, we analyse the Southern Hemisphere (SH) circulation anomalies and the impacts over SSA during the austral summer due to different El Niño patterns (Canonical and El Niño Modoki). The analysis is performed considering reanalysis data and two different Atmospheric General Circulation Models (SPEEDY and UCLA–AGCM). Results from reanalysis show that positive precipitation anomalies develop over SSA during Canonical El Niño events. These anomalies are induced through an increase of upper‐level cyclonic vorticity advection and a stronger low‐level southward moisture transport. However, in El Niño Modoki events, rainfall anomalies are observed over SSA only for the strongest events. Both models are able to reproduce the precipitation signal over SSA in the Canonical El Niño case, although the underlying physical mechanism depends on the model. In SPEEDY, the increased rainfall is due to an increase of the moisture transport toward SSA, while in UCLA–AGCM it is related to both, an increase of the low‐level moisture transport toward SSA and the increase of upper‐level cyclonic vorticity advection. The precipitation signal associated with El Niño Modoki is more controversial. While UCLA–AGCM suggests a rainfall increase over SSA, SPEEDY, in agreement with observations, does not show any statistically significant signal. However, the upper‐level circulation anomalies reproduced by UCLA–AGCM are more consistent with reanalysis than those from SPEEDY, which makes UCLA–AGCM to be more reliable. This result suggests increased rainfall over SSA during El Niño Modoki.

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Analysis of oceans' influence on spring time rainfall variability over Southeastern South America during the 20th century

Cited by 27 publications

References 54 publications

Southern Hemisphere Sensitivity to ENSO Patterns and Intensities: Impacts over Subtropical South America

Southern Hemisphere Sensitivity to ENSO Patterns and Intensities: Impacts over Subtropical South America

Influence of Madden–Julian Oscillation on extreme rainfall events in Spring in southern Uruguay

Southern hemisphere circulation anomalies and impacts over subtropical South America due to different El Niño flavours

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