ISO Modulation on the Submonthly Wave Pattern and Recurving Tropical Cyclones in the Tropical Western North Pacific

Abstract

This study demonstrates the multiscale nature, from synoptic to intraseasonal time scales, of the atmospheric flow in the tropical western North Pacific. The multiscale features include intraseasonal oscillations (ISO), northwestward-propagating submonthly wave patterns, and recurving tropical cyclones (TCs). In the ISO westerly phase, the wave pattern was better organized and the TCs were clustered near the cyclonic circulation of the wave pattern during the genesis, development, and propagation. On the other hand, the wave pattern and TCs were weak and poorly organized in the ISO easterly phase. The distinct characteristics between the westerly and easterly phases could be attributed to the ISO modulation on the monsoon trough and the subtropical anticyclonic ridge. The ISO in the westerly phase provided a favorable background (e.g., enhanced monsoon trough and moisture confluent zone) for the wave–TC pattern development, while the ISO in the easterly phase provided a less favorable environment.