The Intraseasonal Oscillations and Submonthly Wave Patterns over the Western North Pacific

The 5-16-day wave patterns were separated into intraseasonal oscillation (ISO) westerly and easterly phases. The composite results showed that the wave patterns in the westerly phases were better organized and situated in a more intense monsoon trough than its counterpart in the easterly phase. Tropical cyclones (TCs) tended to occur over the cyclonic systems of the wave patterns where the minimal vertical shear axes were also located. More TCs formed in the westerly phases near the areas where the maximal moisture convergence was located. The wave patterns in the westerly phase were located in an area where the warm SST was also located. Therefore, an air-sea interaction could be possible and could enhance the wave activity in the western North Pacific summer.