Fig. 1: Comparison of South Pacific Oscillation between multi-year and single-year ENSO events.
From: South Pacific Oscillation contributes to multi-year ENSOs
a Composite SPO indices for MY and SY El Niño events in FMA1 from 1950 to 2023, and b for MY and SY La Niña events, with error bars indicating the 95% confidence intervals. c Composite monthly SPO indices for MY (red line) and SY (pink line) El Niño events, and d for MY (blue line) and SY (azure line) La Niña events. c, d The evolution of the SPO indices from the first year to the second year of the ENSO lifecycle. All SPO indices are smoothed using a 3-month window and standardized for each calendar month. Dots over the line of MY ENSO represent months where the differences in SPO indices between MY and SY ENSO events are significant at the 95% confidence level. Composite SPO spatial patterns (shading; hPa) in FMA1 for e MY El Niño, f SY El Niño, g MY La Niña, and h SY La Niña. White dots represent the SLP anomalies that are significant at the 95% confidence level. Spatial correlation coefficients (R) between SLP anomalies over the South Pacific (75°S–0°, 180°–90°W) and the typical SPO pattern (Supplementary Fig. 1) are shown in the upper left corner of each panel. Three asterisks indicate that the correlation coefficients have passed the 99% confidence test.
