Multi‐Time Scale Variations in Atlantic Niño and a Relative Atlantic Niño Index

Abstract

Atlantic Niño is a leading mode of climate variability in the tropical Atlantic Ocean with important regional impacts. Tropical Atlantic sea surface temperatures (SSTs) connected with Atlantic Niño exhibit notable multi‐time scale variations, including a quasi‐linear warming trend and sub‐annual to interdecadal variability associated with different physical processes. Contrasting the tropical Pacific SST associated with the El Niño‐Southern Oscillation (ENSO), which has a weak trend and quasi‐periodic oscillatory variability with a period of 2–7 years, the ATL3 index, the primary index for monitoring the Atlantic Niño, has no dominant time scale, that is likely responsible for its low prediction skills. Following the same spirit as the relative Niño3.4 index, we demonstrate that a relative ATL3 index, which is defined as the difference between the raw ATL3 index and the global SST anomaly, provides distinct advantages for monitoring the sub‐annual‐to‐interdecadal variations for Atlantic Niño in real time.