ENSO teleconnections pathways in South America

ENSO events are the most important interannual phenomena impacting climate and weather in South America and have been studied for a long time. Most studies gave special focus on its warm phase (El Nino events) during the austral summer months. However, it is not yet conclusive how the teleconnection patterns are modified according to the different intensities of ENSO events in different seasons and consequently impact South America. Therefore, this study aims to investigate how the different phases, intensities, and seasons of the ENSO events modulate the Stationary Rossby Waves that impact South America. For this, we developed a free and open-source tool called raytracing. The distribution of the SST anomalies influences ENSO intensity. When SST anomalies are higher and spread along the Equatorial Pacific Ocean, ENSO tends to be stronger. This has an impact on the convective source intensity and shapes leading to different Rossby wave sources. Weak ENSO events drive weak anomaly precipitation over South America, mainly in the southeast region. Stationary Rossby waves starting positions are slightly closer to the equator during El Nino over downstream crests/upstream troughs. During La Nina events, they are positioned poleward over downstream troughs/upstream crests. Stationary wavenumbers K-S = 2 and 3 are predominant over South America during El Nino events and DJF La Nina events, while K-S = 2 are predominant in the remaining La Nina events. The wave shape and amplitudes are almost constant during summer events independent of the ENSO intensity, configuring the robustness of the precipitation anomaly patterns over South America. However, in the other seasons, those wave features vary largely, influencing the position and signal of the precipitation anomalies over South America. As a general rule, positive precipitation anomalies regions are associated with a downstream crest and upstream trough in both ENSO phases. While downstream troughs/upstream crests are associated with negative precipitation impacts.

Automated summary

ENSO events have been studied extensively due to their significant impact on climate and weather in South America. Most attention has been given to the warm phase (El Nino events) during the austral summer. However, it is still unclear how the teleconnection patterns are modified based on the different intensities of ENSO events in different seasons, and the subsequent impact on South America. This study aims to investigate how the different phases, intensities, and seasons of ENSO events modulate the Stationary Rossby Waves that impact South America. A tool called raytracing was developed for this purpose. The distribution of SST anomalies influences ENSO intensity, with higher and wider anomalies leading to stronger ENSO events. Weak ENSO events result in weak anomaly precipitation over South America, particularly in the southeast region. The position of stationary Rossby waves varies during El Nino and La Nina events, with El Nino causing them to be slightly closer to the equator and La Nina positioning them poleward. The wave shape and amplitudes remain constant during summer events regardless of ENSO intensity, demonstrating the robustness of precipitation anomaly patterns over South America. However, in other seasons, these wave features exhibit larger variations and heavily influence the position and signal of precipitation anomalies over South America, with positive anomalies associated with downstream crests and negative anomalies associated with downstream troughs/upstream crests.