Combined Effect of the Interdecadal PMM and ENSO on Tropical Cyclones Genesis in the Western North Pacific

In this study, we analyze the differences in tropical cyclones (TCs) genesis characteristics under different combinations of the interdecadal Pacific Meridional Mode (PMM) and the El Niño-Southern Oscillation (ENSO), and explores the possible influencing mechanisms through composite analysis, using IBTrACS v04 and ERA5 reanalysis data. Our results indicate that during the positive (negative) phase of interdecadal PMM, the emergence of El Niño events induces a northward (southward) shift in TC Mean Genesis Location (MGL), and La Niña events result in an eastward (westward) displacement of TC MGL. El Niño events with positive interdecadal PMM phase induce anomalous updrafts north of 20°N, with greater moisture at 700 hPa and smaller vertical wind shear anomalies, so that the TC MGL is more northerly compared to the negative interdecadal PMM phase. During La Niña events with positive interdecadal PMM phase, colder (warmer) sea surface temperature anomalies west of the Philippines (central Pacific) generate downdraft (updrafts) anomalies, and there is greater mid-tropospheric moisture and smaller vertical wind shear anomalies over the eastern WNP, resulting in a more easterly TC MGL than during the negative interdecadal PMM phase. It was also found that ENSO events occurring under interdecadal PMM influence TC generation through modulation of SST in the central Pacific Ocean.These results emphasize that different combined modes of interdecadal PMM and ENSO significantly influence TC genesis and highlight the need to consider the interdecadal PMM phase in future TC forecasts.