Indian Ocean Dipole leads to Atlantic Niño

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.

Impact of Indian Ocean Dipole on Atlantic Niño predictive skill

“…Note that all the hindcasts used here are initialized from September, and CCSM4 and NUIST_CFS1.0 are excluded in the analysis due to the lack of wind data. As suggested by Zhang and Han (2021), the positive rainfall anomalies over the western lobe of the IOD in autumn can trigger an anomalous lower-level cyclonic circulation over the southern tropical Atlantic in the following months, accompanied by westerly wind anomalies in the equatorial eastern Atlantic and northern wind anomalies over western Africa (supplementary figures S3(a)-(d)). Consequently, warm SST anomalies appear along the coast of Angola 1 month after the peak of IOD in SON and then extend to the eastern equatorial Atlantic and peaks in DJF.…”

“…In addition, there are also some Atlantic Niño events peaking in late boreal autumn and winter, which are referred to as the late-onset variety relative to the early-onset type that peaks in boreal summer (Okumura andXie 2006, Vallès-Casanova et al 2020). Zhang and Han (2021) revealed that the Indian Ocean Dipole (IOD) can trigger the Atlantic Niño, especially the late-onset type, via atmospheric teleconnection, with a lead of the former over the latter by ∼3-5 months. Similar results are found by Liao and Wang (2021), who focused on the impact of boreal winter SST anomalies in the Western Indian Ocean (WIO), the domain of which is almost consistent with that of the western lobe of the IOD, on the following summer Atlantic Niño.…”

The Extraordinary Equatorial Atlantic Warming in Late 2019

“…Recent studies have suggested that the tropical Indian Ocean may influence the development of AZM events through changes in the Walker circulation (Liao & Wang, 2021; Zhang & Han, 2021). The 2019 AZM event roughly co‐occurred with one of the strongest Indian Ocean Dipole (IOD; Doi et al., 2020; Saji et al., 1999) events on record.…”

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“…The equatorial Atlantic may also influence the Indian Summer monsoon through atmospheric Kelvin waves (Pottapinjara et al 2014). In turn, it has been and vice versa (Ham et al 2013) but the importance of this pathway is still under debate Zhang et al 2021).…”