Effect of Hadley Circulation–Subtropical Jet Interaction: The Seasonal Contrast of ENSO-Induced Atmospheric Teleconnection Patterns between Boreal Autumn and Winter

Abstract El Niño–Southern Oscillation (ENSO) generates teleconnection patterns that show a marked seasonal contrast in amplitude, with much stronger impacts in boreal winter than in autumn, even when tropical Pacific sea surface temperature (SST) anomalies are of similar magnitude. While previous studies have focused on the effect of background SST in generating convective precipitation anomalies, this study reveals the importance of the position and extent of ENSO-induced regional Hadley circulation (HC) anomalies in forming this seasonal contrast. Unlike traditional zonal-mean diagnostics, the regional HC captures the three-dimensional structure of its interaction with the subtropical jet (STJ), which generates the Rossby wave sources. In winter, the descending branch of the ENSO-induced HC anomaly aligns with the exit of the intensified and eastward-extended STJ. This alignment enhances divergence anomalies, amplifies the Rossby wave source, and drives a stronger downstream teleconnection. In contrast, during autumn, the weaker and poleward-shifted STJ is poorly coupled with the regional HC, limiting wave source generation and weakening the response. This contrast is well captured in observation-based analyses and further validated by numerical model experiments, emphasizing the critical role of regional HC–STJ interaction in shaping ENSO teleconnection seasonality and clarifying the associated Rossby wave dynamics.