The role of the New Guinea cross-equatorial flow in the interannual variability of the western North Pacific summer monsoon

Abstract

The western North Pacific (WNP) monsoon trough from 1958 to 2001 shows a binary-like feature in August and September, with more than half being either an imposing presence or a total absence. One of the major moisture sources maintaining the WNP monsoon trough is the low-level moisture advection laterally driven by the low-level cross-equatorial flow that originates from the Banda Sea and Solomon Sea. By decomposing contributions to the cross-equatorial flow based on the method proposed by Back and Bretherton in 2009, the boundary-layer pressure gradient in the Maritime Continent plays a major role. This pressure gradient is further found to be associated with the densely packed sea surface temperature (SST) gradient near the equator around New Guinea, which is well correlated with the SST anomalies in the equatorial eastern Pacific, a concurrent El Niño/Southern Oscillation (ENSO) condition.