Data availability
All datasets used in this study are publicly available. The RMM index (Wheeler and Hendon 2004) is available at www.bom.gov.au/climate/mjo/graphics/rmm.74toRealtime.txt. For reanalysis and observed data, NOAA Interpolated OLR (Liebmann and Smith 1996) is available at https://psl.noaa.gov/data/gridded/data.interp_OLR.html; NOAA OI SST V2 High Resolution (Reynolds et al. 2007) is available at https://psl.noaa.gov/data/gridded/data.noaa.oisst.v2.highres.html; ERA-5 reanalysis (Hersbach et al. 2020) is available at https://cds.climate.copernicus.eu/#!/search?text=ERA5&type=dataset; and ERA-20C data (Poli et al. 2016) is available at https://www.ecmwf.int/en/forecasts/datasets/reanalysis-datasets/era-20c.