Fig. 5: Sea surface temperature and moist static energy background state of the three different Boreal Summer Intraseasonal Oscillation propagation modes.

Background states for sea surface temperature (SST) (a, c, e) and moist static energy (MSE) (b, d, f) for the Canonical (1st row), Eastward Blocked (2nd row), and Quasi-stationary propagation modes (3rd row). Composited anomalies of background column-integrated MSE and SST conditions are shown for days averaged 25–30 days before day 0 (as defined by the days of maximum synchronization), relative to the JJAS climatology. Stipples indicate significance at the 95% confidence level using Student’s t-test. The dashed lines indicate the region of the Maritime Continent barrier (110° E to 130° E, compare Fig. 4c, e).