A mechanism of interdecadal variability of tropical cyclone activity over the western North Pacific

Tropical cyclone (TC) activity in the western North Pacific (WNP) has changed interdecadally with an approximately 20-year period between 1951 and 1999. The cause and mechanism of interdecadal variability of TC frequency in the WNP is investigated using NCEP/NCAR reanalysis and the result obtained from a high-resolution coupled general circulation model (CGCM). The interdecadal variability of TC activity in the WNP correlates with long-term variations in sea surface temperatures (SSTs) in the tropical central Pacific and with those of westerly wind anomalies associated with the monsoon trough that appears over the tropical WNP during the typhoon season of July to October. The westerly wind anomalies at near 10degreesN show positive feedback with the SST anomalies in the central Pacific. Therefore, the interdecadal variability of TC frequency is related to long-term variations in atmosphere-ocean coupling phenomena in the tropical North Pacific. A 50-year long-run simulation using the high-resolution CGCM showed the robustness of interdecadal variability of TC frequency.