Interdecadal weakening of the cross-equatorial flows over the Maritime Continent during the boreal summer in the mid-1990s: drivers and physical processes

Abstract In this study, the cross-equatorial flows (CEF) on both high and low level (HCEF/LCEF) troposphere over Maritime Continent (MC) in boreal summer are found to have experienced an interdecadal weakening mid-1990s based JRA55 NCEP reanalyses. The outputs of 8 coupled models CMIP6 used investigate drivers corresponding mechanisms. Model results show that role external forcing is weak CEF. By contrast, observed HCEF LCEF can be largely explained by internal variability associated with a negative phase Pacific Oscillation (IPO). Associated IPO anomalous divergence (convergence), enhanced precipitation MC cyclonic (anticyclonic) circulations, reduced western North (WNP) upper (lower) troposphere. Sensitivity experiments MetUM-GA6 further manifest transition lead CEF, which central tropical (CTP) sea surface temperature (SST) anomalies play dominant role. cold SST CTP local convection trigger through changes Walker circulation. leads change Hadley circulation sector. This characterized ascents MC, southerlies troposphere, descents WNP northerlies lower leading Meanwhile, positive also make contribution CEF inducing sector similar processes.