Fig. 3

MJO propagation in a varying background SST (°C) simulated in the trio-interaction model with B-M scheme. a Idealized Indo-Pacific warm pool SST configuration. b Time-longitude diagram of simulated precipitation rate (mm/day) along the equator; c simulated normalized low-level (700-hPa) wind (vectors), geopotential height (contour) and the precipitation (shading) at day 7; d observed horizontal structures of MJO during winter (NDJFM), namely regressions of 700-hPa wind (m/s, vector), geopotential height (m, contour), as well as precipitation (mm/day, shading) with respect to the precipitation index over the eastern Indian Ocean (averaged over 5°S–5°N; and 70°E–90°E); e the simulated equatorial (averaged between 5°S and 5°N) precipitation (red), column-integrated moisture (green) and BL convergence (blue); f the same as e except for observation; g Planetary zonal scale of the MJO mode shown by the low-level equatorial zonal wind (m/s) at day 7 (blue line). The red line shows the approximate zonal wind made by the first four wavenumbers; h the same as g, except for the observed MJO zonal scale corresponding to d. The observational datasets are ERA-interim atmospheric dataset and TRMM precipitation dataset, with a period from 1998 to 2015