Relationship between interhemispheric Rossby wave propagation and South Atlantic convergence zone during La Nina years

Through a set of observational analyses and baroclinic model experiments, we show that during La Nina conditions a wave train in North Pacific propagates eastwards along the Asian jet, crosses the equator and interacts with the SACZ through an equatorial window in the East Pacific. Composites of active SACZ for November-March of 1979-2013 are used, drawn from the full dataset and also from just the La Nina years. The data are filtered in two-time bands: 20-90days (intraseasonal) and >200days (interannual). Interhemispheric waveguides are identified in the anomalous SACZ composites during La Nina years. A similar wave pattern is simulated by a baroclinic atmospheric model with a fixed La Nina basic state where a thermal forcing anomaly is added on Southeast Asia. This La Nina basic state favours anomalous westerly equatorial flow at high levels, enabling a connection between Asia and South America around 15days.