Distinct decadal modulation of Atlantic-Niño influence on ENSO

Abstract

It is known that winter Atlantic-Niño events can induce the El Niño–Southern oscillation (ENSO) in the following winter with a lag of 1-year during one period. On the other hand, summer Atlantic-Niño events can lead to the ENSO in the subsequent winter with a half-year lag during another period. In this study, we investigate the distinct interdecadal modulation of the effect of the Atlantic-Niños on ENSO by analyzing observational reanalysis datasets. During the mid-twentieth century, the winter Atlantic-Niño exhibited increased intensity and extended westward due to warmer conditions in the tropical western Atlantic. As a result, convection occurred from the Amazon to the Atlantic, triggering an atmospheric teleconnection that led to trade wind discharging and equatorial Kelvin waves, ultimately contributing to the development of ENSO. In contrast, during late twentieth century, summer Atlantic-Niño events were closely linked to the South America low-level jet in boreal spring. This connection led to the formation of widespread and intense convection over the Amazon to the Atlantic region. Then, the Walker circulation was effectively modulated, subsequently triggering ENSO events. Further analysis revealed that the interdecadal modulation of the Atlantic–South America–Pacific mean state plays a crucial role in shaping the impact of Atlantic-Niños on ENSO by modifying not only the characteristics of the Atlantic-Niños but also ocean–atmospheric feedback process. Therefore, improving our understanding of the interdecadal modulation of the climatological mean state over the Pacific to Atlantic regions enables better anticipation of the interaction between the Atlantic and Pacific Oceans.

Tropical Atmospheric Response of Atlantic Niños to Changes in the Ocean Background State

“…We find that during 1975–1985 the tropical South Atlantic and eastern Pacific is warmer, and the ITCZ is shifted south toward the equator. An equatorward shifted ITCZ can facilitate a stronger atmospheric response of the equatorial Pacific (Park et al., 2023). The atmospheric response to an Atlantic Niño given this background state reflects a more westward location of surface convergence and upper‐level divergence in the Atlantic with respect to the response during 1950–1960.…”

“…Furthermore, Atlantic Niño variability may also be weakening (Crespo et al., 2022; Prigent et al., 2020; Yang et al., 2022), which could reduce the atmospheric response to Atlantic Niños. On the other hand, the boreal winter peak of the Atlantic Niño could become more important for ENSO predictions as the summer peak weakens (Hounsou‐Gbo et al., 2020; Park et al., 2023). Lastly, the results here also suggest that the ANN‐ENSO teleconnections can be hampered in models by systematic biases in the global SST pattern and the ITCZ position.…”

The Asymmetric Predictive Power of Indian Ocean Dipole for Subsequent Year's ENSO: Role of Atlantic Ocean as an Intermediary

“…Previous studies (e.g., Park et al, 2023) found that the influence of "summer" Atlantic Niño on ENSO has strengthened since the late 1970s (Figure S7 in Supporting Information S1). However, our focus is on the "winter" Atlantic Niño, and its relationship with subsequent ENSO has remained remarkably constant in recent years (dashed line in Figure S7 in Supporting Information S1; purple line in Figure S8 in Supporting Information S1).…”

Multi-decadal Changes of the Impact of El Niño Events on Tibetan Plateau Summer Precipitation

“…As El Niño decays during the summer, the Indo-western Pacific Ocean capacitor effect sustains the warming of SST in the tropical North Indian Ocean [21] , thus maintaining the impact of ENSO on TP summer precipitation. With regard to the North Atlantic SST, El Niño can trigger a tripolar SST pattern in the North Atlantic, a phenomenon that often persists into the summer [24] . This tripolar pattern exerts a remote influence on the summer precipitation in the Tibetan Plateau through teleconnections [25] .…”