Fig. 4: The roles of three tropical oceans during SON.

a Scatter plot of observed Pacific SST anomalies averaged over the tropical Pacific (160°E–80°W, 10°S–10°N) and 850-hPa zonal wind anomalies averaged over 140°E–140°W, 0°–10°N. b Simulated response of 850-hPa zonal wind anomalies to SST forcing in three tropical oceans, the Pacific, the Indian Ocean and the Atlantic experiments, respectively. Results from SST forcing experiments for: c Tropical Pacific Ocean (blue shading in Fig. S4); d Tropical Indian Ocean (green shading in Fig. S4). e Results from tropical Atlantic heat source anomaly experiment (shading in Fig. S6a). Vector and shading represent the anomalous 850-hPa horizontal wind (unit: m/s) and precipitation (unit: mm), respectively. Both are statistically significant at the 95% confidence level based on Student’s t-test. Brown and blue contours indicate high-level convergence and divergence, respectively. Thick brown (blue) contours represent 2 × 10⁶ (−2 × 10⁶) m²/s. Contour interval is 1 × 10⁶ (−1 × 10⁶) m²/s. The wind anomaly of less than 1 m/s is omitted.