Cross-Equatorial Surges Boost MJO's Southward Detour Over the Maritime Continent

The influence of the cross-equatorial northerly surge (CES) on the eastward propagation of Madden-Julian oscillation (MJO) during boreal winter is evaluated through the analysis of the column integrated moisture budget. Results show that the CES reinforces MJO's southward detour by increasing horizontal moisture convergence over the southern Maritime Continent (MC) region. Further analysis reveals that the zonal convergence by intraseasonal zonal wind anomalies acting upon background moisture is intensified in the presence of CES events, causing a stronger convective activity in the southern MC (SMC). The stronger moisture convergence in the SMC is associated with the CES-induced intensification of low-level northwesterly and westerly winds, which, in turn, strengthen zonal wind convergences and positive wind-evaporation feedbacks onto the MJO convection. An improved process understanding of the link between the CES and MJO detours can help engender improvements in extreme weather forecasts and aid investigation biases in simulating MJO in climate models.

Automated summary

The influence of the cross-equatorial northerly surge (CES) on the eastward propagation of Madden-Julian oscillation (MJO) during boreal winter is evaluated through the analysis of the column integrated moisture budget. The study reveals that the CES reinforces MJO's southward detour by increasing horizontal moisture convergence over the southern Maritime Continent (MC) region. Further analysis shows that the stronger moisture convergence in the southern MC is associated with the CES-induced intensification of low-level northwesterly and westerly winds, which strengthen zonal wind convergences and positive wind-evaporation feedbacks onto the MJO convection.