Causal interactions between ENSO and the North Tropical Atlantic

Abstract. The global climate is impacted by several major climate modes including the North Tropical Atlantic mode (NTA) and the El Niño–Southern Oscillation (ENSO). Although NTA and ENSO are suggested to have connections, there is uncertainty regarding the causal relationship between these climate modes. While previous works focused on the correlation between NTA and ENSO, causal analyses accounting for the influence of other tropical climate modes are lacking. Here we investigate the causal links between ENSO and NTA using outputs from high-resolution climate model simulations and reanalysis data. Our results suggest robust causal effects of ENSO on NTA and provide insights on the unstable impacts of NTA on ENSO. We observe high consistency between reanalysis data and the models in mimicking the impacts of ENSO on North Tropical Atlantic region. Specifically, most models (14 over 20) and reanalysis data revealed that ENSO is very unlikely to have no causal impacts on NTA. However, there is diverse response of the tropical Pacific to NTA between reanalysis data and the models. While reanalysis data indicates possible impacts of NTA on ENSO and sea surface temperature over the equatorial Pacific, the majority of models (18 over 20) suggest that the NTA is likely to have no causal effects on ENSO. Hence, the models may underestimate the causal effects of NTA on ENSO, implying that better representation of NTA variability and NTA-ENSO causal connections in the models may improve the predictability of ENSO variations.