Impacts of monsoon break events in the western North Pacific on the cross-equatorial flows over the Maritime Continent

This study examines the possible impacts of western North Pacific (WNP) monsoon break events on the crossequatorial flows (CEFs) over the Maritime Continent using daily data from ERA5 for 1979-2020. It reveals that WNP monsoon break events can cause significant weakening of CEF in the both upper and lower troposphere, i.e., weaker southerlies in the lower level and northerlies in the upper level. These CEF anomalies are associated with a baroclinic structure of circulation anomalies over the WNP, consisting of upper-level cyclonic and lower-level anticyclonic anomalies. Furthermore, statistical analysis indicates that WNP monsoon break events correspond more closely to weakening of upper-level CEF, in comparison with lower-level CEF: 92% of WNP monsoon break events correspond to upper-level CEF weakening, while this decreases to 70% for lower-level CEF. This relatively lower proportion for lower-level CEF is largely attributable to the impact of the warm phase of ENSO.