Indian Ocean role in the ENSO teleconnection to the Euro-Atlantic region from early to late winter

El Niño Southern Oscillation (ENSO) weakly influences the seasonal mean Euro-Atlantic circulation anomalies during boreal winter season. It is important to understand the intra-seasonal characteristics of ENSO teleconnections with Euro-Atlantic sector during the boreal winter season. We noted a transition of the Euro-Atlantic circulation anomalies in response to ENSO from early to late winter. During earlier winter, a positive ENSO phase enforces an east-west rainfall dipole anomaly in tropical Indian Ocean, with an increased (reduced) rainfall over the western (eastern) Indian Ocean, which weakens in late winter. In early winter ENSO through Indian Ocean rainfall dipole modulates the subtropical South Asian jet (SAJET), enforces a wavenumber-3 response projecting spatially onto the positive North Atlantic Oscillation (NAO) pattern. On contrary, during late winter, the direct ENSO wavetrain emanating from the tropical Pacific region, involving Pacific North American (PNA) pattern anomalies project spatially on the negative phase of the NAO. The Indian Ocean dipole is partly enforced by the ENSO atmospheric teleconnections but can also exist independently. Atmospheric General Circulation Model (AGCM) numerical experiments forced with an Indian Ocean heating dipole anomaly support the hypothesis. This mechanism was further analyzed in un-initialized (CMIP5) as well as in initialized simulations using ECMWF-SEAS5 hindcast dataset. Both types of model reproduce the observed ENSO-forced inter-basin tropical teleconnections transition from early to late winter and their response to the Euro-Atlantic circulation anomalies quite well. Thus, the tropical inter-basin connections might be a key to improve the understanding of the sub-seasonal to seasonal variability and predictability of the Euro-Atlantic circulation anomalies.