Interactions between the TC/submonthly Wave Pattern and ISO in the Western North Pacific

Abstract Interactions between the TC/submonthly Wave Pattern and ISO in the Western North Pacific are explored. The wave pattern exhibited an equivalent barotropic structure with the maximum vorticity and kinetic energy in the lower troposphere and propagated northwestward in the Philippine Sea in the intraseasonal oscillation (ISO) westerly phase and north-northeastward near the East Asian coast in the easterly phase. The mean flow advection played a dominant role in the propagation in both phases.

Barotropic energy conversion is the dominant process in maintaining the kinetic energy of the pattern. The wave pattern tended to occur in the confluent zone between the monsoon trough and the anticyclonic ridge, where the kinetic energy could be efficiently extracted from the westerly mean flow associated with the monsoon trough. The individual circulation circuit embedded in the pattern was oriented in the northeast-southwest (east-west) orientation to have optimal growth and propagation during the ISO westerly (easterly) phase.