Modulation of Typhoon Tracks over the Western North Pacific by the Intraseasonal Oscillation

The modulation of the intraseasonal oscillation (ISO) on the typhoon tracks over the western North Pacific is studied by observational data analysis. The authors divide the main classes of typhoon tracks into five types based on the traditional methods. The results show that the ISO may affect the tracks of typhoons. The low-frequency cyclone (LFC) or low-frequency anticyclone (LFAC) influences the intensity and position of the monsoon trough and subtropical high in the lower and middle troposphere. The LFC east of the Philippines will strengthen the monsoon trough, and its northward propagation will influence the position of the subtropical high so as to influence the typhoon activity. Afterward, typhoons are more inclined to move along the zone of positive vorticity of the LFC. The ISO westward propagation in the form of wave trains in the subtropics also influences the position of subtropical high. The interaction of tropical and subtropical ISOs performs an important function on the typhoon tracks. The low-frequency circulation at 200 hPa can also have an indicative effect on the typhoon tracks. As a whole, the circulation field of ISO can be used as a basis for forecasting the typhoon tracks.