Distinct decadal modulation of Atlantic-Niño influence on ENSO

Abstract

AbstractThe summer and winter Atlantic-Niño events are capable of triggering the El Niño–Southern oscillation (ENSO) in the subsequent winter with half-year and one-year leads, respectively. Here, we examine the interdecadal modulation of the effect of the Atlantic-Niños on ENSO by analyzing observational reanalysis datasets. During mid-Twentieth Century, the winter Atlantic-Niño intensified and expanded westward as a result of local warm and humid climates. Accordingly, convection occurred from the Amazon to the Atlantic, and the resulting atmospheric teleconnection induced trade wind discharging and equatorial Kelvin waves, leading to the development of ENSO. In contrast, during late-Twentieth Century, summer Atlantic-Niño events expanded westward as linked to the South American low-level jet, which induced strong convection over the Amazon to the Atlantic. This caused a modulated Walker circulation, which in turn triggered ENSO. We conclude that the prerequisite for the lagged relationship between Atlantic-Niño and ENSO events is a wide convection over the tropical South America to the Atlantic, which influences the level of atmospheric teleconnection toward the Pacific. It seems that climatological Pacific mean state plays some role in determining the lead-time of the Atlantic-Nino effect on the ENSO.