Tropical climate variability: interactions across the Pacific, Indian, and Atlantic Oceans

Modes of tropical climate variability, such as the El Niño– Southern Oscillation (ENSO), the Indian Ocean Basinwide Mode (IOBM), the Indian Ocean Dipole (IOD), and the Atlantic Equatorial Mode (AEM) (sometimes referred to as the Atlantic Zonal Mode, or Atlantic Niño) interact most readily via the atmosphere. Sea surface temperature anomalies (SSTAs) in the tropics drive changes in the Walker Circulation, which in turn influence SSTAs in remote regions, hence forming a teleconnection (e.g., Lau and Nath 1996; Klein et al. 1999; Alexander et al. 2002). Through this atmospheric teleconnection mechanism, modes in one ocean basin can be damped, enhanced, or even entirely generated by a mode in another ocean basin. Oceanic pathways also provide the means for inter-basin interactions, although at lag times typically beyond several months. Whilst the literature is rich on the interactions between ENSO and each of the tropical modes in the Indian and Atlantic Oceans, few studies have examined the possible interactions between the Indian and Atlantic modes, apart from the Atlantic influence on the Indian monsoon (e.g. Kucharski et al. 2008; Losada et al. 2010). Furthermore, if all three tropical basins are strongly coupled, then interactions between any two basins can be influenced or modulated by the third ocean basin. This aspect, which has previously been neglected in the literature, will be considered here. A better understanding of these highly complex inter-basin interactions is relevant for improving climate prediction, especially for ENSO (e.g. Izumo et al. 2010; Keenlyside et al. 2013). Abstract Complex interactions manifest between modes of tropical climate variability across the Pacific, Indian, and Atlantic Oceans. For example, the El Niño–Southern Oscillation (ENSO) extends its influence on modes of variability in the tropical Indian and Atlantic Oceans, which in turn feed back onto ENSO. Interactions between pairs of modes can alter their strength, periodicity, seasonality, and ultimately their predictability, yet little is known about the role that a third mode plays. Here we examine the interactions and relative influences between pairs of climate modes using ensembles of 100-year partially coupled experiments in an otherwise fully coupled general circulation model. In these experiments, the air–sea interaction over each tropical ocean basin, as well as pairs of ocean basins, is suppressed in turn. We find that Indian Ocean variability has a net damping effect on ENSO and Atlantic Ocean variability, and conversely they each promote Indian Ocean variability. The connection between the Pacific and the Atlantic is most clearly revealed in the absence of Indian Ocean variability. Our model runs suggest a weak damping influence by Atlantic variability on ENSO, and an enhancing influence by ENSO on Atlantic variability.