Internal Precipitation and Kinematic Structure of the South Pacific Convergence Zone

Abstract

This study investigated the internal precipitation and kinematic structure of the South Pacific convergence zone (SPCZ) observed by the Doppler radar aboard the research vessel Mirai, which passed through the western tropical portion of the SPCZ on 17–21 December 2016. Convective precipitation developed in association with the low-level convergence induced by the monsoon and the upper-level divergence associated with extratropical Rossby wave breaking. Mesoscale convective systems (MCSs) developed from either intersecting (northeast–southwest/ northwest–southeast) or zonally oriented convective bands. For the MCS developing from the former mode, the zonal and meridional divergence fields made comparable contributions to convective development. For the MCS developing from the latter mode, the divergence field induced by the meridional wind had the largest contribution to producing convection. The MCS with stronger convective updrafts and higher echo tops and coverage occurred in the region where more intense convergence was observed near the surface. The results of this study highlight the dependence of organizational modes of SPCZ convection on the coupling of the tropical low-level and extratropical upper-level forcings, as well as on the zonal and meridional forcing structures.