The non-stationary influence of the Atlantic and Pacific Niños on North Eastern South American rainfall

Abstract

Rainfall variability over the tropical Atlantic region is dominated by changes in the surface temperature of the surrounding oceans. In particular, the oceanic forcing over Northeast of South America is dominated by the Atlantic interhemispheric temperature gradient, which leads its predictability. Nevertheless, in recent decades, the SST influence on rainfall variability in some tropical Atlantic regions has been found to be non-stationary, with important changes of the Atlantic and Pacific influence on Sahelian rainfall which appear to be modulated at multidecadal timescales. In this work, we revisit the SST influence over Northeast of South America including the analysis of the stationarity of this relationship at interannual timescales. Principal Component Analysis has been applied to the interannual component of rainfall during the March-April-May season. Results show how the SST forcing on the first mode of rainfall variability, which is a dipole-like pattern generated by the changes in the seasonal migration of the Intertropical Convergence Zone, is different depending of the considered period. The response to the SST anomalies in the Pacific basin is opposite to the Atlantic one and affects different areas. The Atlantic Niño influences rainfall variability at the beginning of the XX century and after 1970, while the Pacific Niño plays a major role in the variability of the rainfall in the Northeast of South America from 1970 onwards. The combined effect of both basins after the 1970s amplifies the anomalous rainfall response.

The Teleconnection of the Tropical Atlantic to Indo-Pacific Sea Surface Temperatures on Inter-Annual to Centennial Time Scales: A Review of Recent Findings

“…The impact of the Atlantic-Pacific connection on teleconnections is also important as, during boreal summer months, the concomitant effect of the Atlantic and Pacific on remote regions as Sahel, has been found to produce counteracting effects affecting rainfall predictability ( [55,56]). In addition, it has been found how the Atlantic-Pacific connection affects over north eastern southamerican rainfall ( [57]) or boreal summer mediterranean rainfall ( [58]). …”

The Influence of Recurrent Modes of Climate Variability on the Occurrence of Monthly Temperature Extremes Over South America

“…Figure shows the association percentages for ANINO months with T90 and T10 for DJF and MAM. These seasons are chosen to capture the documented influence that the ANINO has on the position of the with precipitation influences over portions of SA (Torralba et al, ). In DJF, the T90 months (Figure a) are significantly associated with ANINO+ in a band stretching from southern Bolivia north to the Pacific Coast of Colombia with particularly high values and spatially coherent data set agreement in a region encompassing northern Bolivia and the Brazilian states of Acre, southern Amazonas, and Rondonia.…”

“…T10 ANINO− values (Figure d) are mostly significant in a region south of Northeast Brazil. Torralba et al () document the influence of the ANINO on precipitation over northeastern SA and demonstrate a modulation of the seasonal extent of the during MAM in response to Atlantic SST variability. Our results suggest that temperature anomalies do not present the same behavior as precipitation anomalies in relation to the ANINO in this region.…”

“…This supports the conjecture that extreme cold months are influenced by an anomalous reduction in insolation due to clouds, while T90 months are associated with increased solar heating. Positive phases of the ANINO are associated with a southward shift of the ITCZ during the northeastern SA rainy season (Torralba et al, ); however, it is not a priori clear that the precipitation anomalies associated with extreme temperatures in Figure result from anomalous excursions of the ITCZ. Another potential pathway is through anomalous 850 hPa winds, which can act to advect high moist static energy from the west to enhance convective precipitation or low moist static energy from the Atlantic Ocean limiting convective precipitation in this region of high‐precipitation variability (Ma et al, ).…”

“…Rusticucci and Vargas () document the influence of ENSO on the occurrence and persistence of warm and cold episodes over Argentina. Sea surface temperature (SST) variability in the tropical Atlantic Ocean (i.e., the Atlantic Niño) has also been shown to be associated with climate impacts, especially over northeastern SA through modulation in the position of the Intertropical Convergence Zone (ITCZ; Hastenrath & Greischar, ; Mechoso & Lyons, ; Torralba et al, ; Zebiak, ).…”