Assessing Tropical Basin Interactions in SEAS5-20C. Impact on ENSO predictability

El Niño is the leading mode of interannual climate variability, driving seasonal predictability worldwide. It has been found that tropical variability, as that in the Atlantic, can impact on ENSO in certain decades, affecting its predictability. Nevertheless, a comprenhensive analysis of the role of the Tropical Atlantic in changing ENSO predictability along time has not been assessed so far. This work analyses the Atlantic-Pacific connection and its impact on ENSO prediction using the 20th century reforecast of the ECMWF operational seasonal forecast model, SEAS5-20C, for which changes in ENSO predictive skill over the century have been previously found. Using this reforecast, multidecadal variability of tropical basin interactions appear together with changes in tropical Atlantic and Pacific predictability. It is found how the connection between tropical basins is related to the improvement in ENSO prediction, even in the second year after the initialization (+12 month lead-time), confirming that changes in the background conditions modulates these changes in predictability.