Supplementary Table 1. Overview of climatic indices used as measures of the Walker circulation strength, including their temporal and spatial range. Indirect measures, such as the ocean surface current speed along the equator, are also included. Note that the SSH dataset we used contains only SSH anomalies, consequently to obtain SSH difference between the east and west equatorial Pacific, we first compute the time-mean SSH for each grid based on the AVISO dataset (AVISO, 2011), then we add these background SSH values to the sea-surface height anomaly (MEaSUREs Gridded Sea Surface Height Anomalies v1812).