Abstract
The impact of intraseasonal oscillation on tropical cyclone genesis (TCG) over the western North Pacific during boreal summer was examined in association with categorized synoptic-scale low-level flow patterns. Five synoptic-scale flow patterns were considered as synoptic-scale environment connecting the large-scale intraseasonal oscillation and meso-scale TCG: a shear line, a confluence region, an easterly wave, a monsoon gyre, and a pre-existing tropical cyclone. The phase and amplitude of the boreal summer intraseasonal oscillation (BSISO) were used. It is found that the phase 7 was favorable for TCG associated with the shear line, and the phases 7 and 8 were also favorable for TCG associated with the confluence region. During the favorable phases for each flow pattern associated with TCG, the BSISO affected the large-scale zonal wind distribution, and the large-scale zonal wind forms synoptic-scale flow patterns over the suitable environment for TCG. The link between the intraseasonal oscillation and synoptic-scale flow patterns is an important factor in TCG.
