Summer and winter Atlantic Niño: connections with ENSO and implications

Abstract

The teleconnection between the Atlantic Niño and the Pacifc El Niño Southern Oscillation (ENSO) is revisited using observational and reanalysis data for the 1905–2014 period. Two types of Atlantic Niño are signifcantly negatively correlated with ENSO, with Atlantic leading ENSO by 6-month to 1-year. The frst one is the already well-known connection between the boreal summer Atlantic Niño (ATL3: 3° N–3° S, 20° W–0°) and the subsequent winter ENSO (Niño3: 5° N–5° S, 150° W–90° W). This relationship is strong in the frst and last decades of the study period. It is shown that a second Atlantic Niño in boreal fall/early winter (October–December, hereinafter called winter Atlantic Niño) is also signifcantly correlated with the following year ENSO. This winter Atlantic Niño leads to an early development of ENSO from boreal summer onwards, with a marked multidecadal modulation of the lead time. A nearly 1-year leading connection between winter Atlantic Niño and the following ENSO is generally observed in the mid-twentieth century, mostly when the summer Atlantic Niño teleconnection with the subsequent winter ENSO is weak. The same mechanism of the Atlantic–Pacifc Niño connection, which involves the Walker circulation, operates for the two types of Atlantic Niño. Our analysis supports the leading infuence of the summer and winter Atlantic equatorial modes on climate variability in South America. These results suggest the relevance of diferent types of Atlantic Niño for the 6-month to 1-year predictability of ENSO and its climatic impacts.