Distinct decadal modulation of Atlantic-Nino influence on ENSO

Abstract

It is known that winter Atlantic-Nino events can induce the El Nino-Southern oscillation (ENSO) in the following winter with a lag of 1-year during one period. On the other hand, summer Atlantic-Nino 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-Ninos on ENSO by analyzing observational reanalysis datasets. During the mid-twentieth century, the winter Atlantic-Nino 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-Nino 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-Ninos on ENSO by modifying not only the characteristics of the Atlantic-Ninos 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.