Interannual Characteristics of Tropical Cyclones in Northwestern Pacific Region in Context of Warm Pool and Monsoon Troughs

This study utilizes the typhoon path ensemble dataset from the Marine Science Big Data Center, surface temperature data from NOAA’s COBE Sea Surface Temperature dataset, and wind field data from the NCEP/DOE Reanalysis II dataset. It employs analytical techniques such as wavelet analysis, correlation analysis, and the Mann–Kendall test to investigate the temporal and spatial variations in tropical cyclones in the Northwest Pacific, focusing on aspects such as frequency, genesis regions, and Accumulated Cyclone Energy. The research examines the influence of environmental factors, including warm pool thermal conditions and monsoon troughs, on the behavior of tropical cyclones. Findings indicate that over the past 39 years, there has been an upward trend in the frequency of tropical cyclones, whereas ACE has exhibited a slight downward trend. The results of the M-K test suggest that following a period of rapid increase, cyclone frequency experienced a significant shift in 1996, subsequently displaying a downward trend. Notably, the frequency of cyclones aligns with mutation points corresponding to warm pool thermal conditions and the Monsoon Trough Index. Wavelet analysis reveals that cyclone frequency, ACE, warm pool thermal conditions, and MTI exhibit similar small scale periodic variations. The observed differences in the genesis regions of tropical cyclones are attributed to fluctuations in warm pool thermal conditions. Specifically, years characterized by cooler warm pool conditions correspond with a stronger MTI, while warmer conditions are associated with a weaker MTI. The genesis regions of cyclones predominantly lie within the monsoon trough, where environmental conditions favorable for cyclone development are intensified during years of cooler warm pool conditions, resulting in heightened convective activity.