Abstract
Atlantic Niño is the Atlantic equivalent of El Niño-Southern Oscillation (ENSO), and it has prominent impacts on regional and global climate. Existing studies suggest that the Atlantic Niño may arise from local atmosphere-ocean interaction and is sometimes triggered by the Atlantic Meridional Mode (AMM), with overall weak ENSO contribution. By analyzing observational datasets and performing numerical model experiments, here we show that the Atlantic Niño can be induced by the Indian Ocean Dipole (IOD). We find that the enhanced rainfall in the western tropical Indian Ocean during positive IOD weakens the easterly trade winds over the tropical Atlantic, causing warm anomalies in the central and eastern equatorial Atlantic basin and therefore triggering the Atlantic Niño. Our finding suggests that the cross-basin impact from the tropical Indian Ocean plays a more important role in affecting interannual climate variability than previously thought.
Highlights
Atlantic Niño is the Atlantic equivalent of El Niño-Southern Oscillation (ENSO), and it has prominent impacts on regional and global climate
To understand the possible impact of the Indian Ocean Dipole (IOD) on Atlantic Niño, we first perform a lead-lag regression of sea surface temperature (SST) and wind anomalies on the Dipole Mode Index (DMI), an index for the IOD defined as the difference of SST anomalies (SSTA) between western and eastern tropical Indian Ocean[34]
Our results show that SSTA of the phase of the IOD (pIOD) starts to develop ~5 months prior to its peak, accompanied by easterly wind anomalies over the tropical Indian Ocean (Figs. 1b, c and 2)
Summary
Atlantic Niño is the Atlantic equivalent of El Niño-Southern Oscillation (ENSO), and it has prominent impacts on regional and global climate. We find that the enhanced rainfall in the western tropical Indian Ocean during positive IOD weakens the easterly trade winds over the tropical Atlantic, causing warm anomalies in the central and eastern equatorial Atlantic basin and triggering the Atlantic Niño. The east-west SST gradient, is substantially weakened or even reversed in some years, which is accompanied by a significant slackening of the trade winds[1] This climate phenomenon is called El Niño, the positive phase of El NiñoSouthern Oscillation (ENSO), in the tropical Pacific[2] and is referred to as the Atlantic Niño in the tropical Atlantic[3]. The associated eastward SLP gradient force induces westerly wind anomalies, which cause anomalous surface Ekman convergence, deepen the thermocline, reduce oceanic upwelling cooling and further increase the warm SSTA in the eastern basin. Surface heat flux anomalies do not contribute much to the warm SSTA associated with the Atlantic Niño[25]
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