Revisiting the interannual impact of the Pacific Meridional Mode on tropical cyclone genesis frequency in the Western North Pacific

Several studies have discussed the interannual influences of the North Pacific Meridional Mode (PMM) on the tropical cyclone (TC) in the western North Pacific (WNP). However, most of them either mixed the contributions of the PMM and Pacific decadal modes or failed to separate the PMM and El Nino-Southern Oscillation (ENSO) impacts. Here, we systematically revisited the year-to-year relationship between the PMM and WNP TC activity, including TC genesis frequency (TCGF) and TC track density (TCTD), by removing decadal variability. The results show that positive (negative) PMM events can induce anomalous basin-uniform cyclonic (anticyclonic) circulation and lead to a significant increase (decrease) in TCGF and TCTD over the WNP. The relationship between TCGF and the PMM is modulated by the ENSO events. When the positive PMM events are synchronized with the El Nino phase, they can enhance southeastern quadrant TC genesis over the WNP and increase TCTD in the whole WNP. However, when the positive PMM events are in phase with La Nina events, it shows an insignificant impact on WNP TCs due to the reverse influence of PMM and ENSO. This study emphasizes the important influence of the PMM on WNP TC activity on interannual time scale, especially during neutral ENSO years.