Phase-dependent modulation of the MJO during cross-equatorial northerly surges (CENS)

This study investigates phase-dependent associations between Cross-Equatorial Northerly Surges (CENS) and Madden-Julian Oscillation (MJO) precipitation and circulation patterns using 84 years (1940–2023). Approximately 79% of CENS days (76% of events) occurred during phases 4–7 of the active MJO. Composite analysis reveals distinct phase-dependent co-variations between CENS occurrence and MJO structure: during phases 4–5 (MJO over the Maritime Continent), CENS occurrence is associated with enhanced precipitation around Java and along the northern coast of Australia through enhanced meridional convergence. In contrast, during phases 6–7 (MJO over the Western Pacific), CENS-associated patterns are meridionally broader and vertically deeper, with enhanced precipitation over the western flank (rear) of the MJO. Notably, phases 6–7 exhibit significant positive sea surface temperature anomalies in the Western Pacific, a pattern that persists even when controlling for ENSO phase and MJO amplitude variations, consistent with a southward shift of the MJO propagation path. These results indicate that CENS are not merely passively affected by the MJO but are systematically associated with distinct phase-dependent differences in MJO precipitation patterns, vertical structure, and propagation characteristics.