Cause of interdecadal change of tropical cyclone controlling parameter in the western North Pacific

The interdecadal change of tropical cyclone (TC) controlling parameter in the western North Pacific (WNP) was investigated using observational data. Through the diagnosis of the relative role of each term of the TC genesis potential index (GPI), it was found that the dominant factor controlling interannual TC genesis frequency was specific humidity in 1950–1976, maximum potential intensity or sea surface temperature (SST) in 1977–1998, and relative vorticity in 1999–2014. The change of environmental specific humidity during 1950–1976 was primarily attributed to the advection of the mean moisture by anomalous low-level wind in ENSO developing summer. The change of SST during 1977–1998 was primarily affected by a V-shape SST pattern in western Pacific in ENSO decaying summer. The change of environment relative vorticity during 1999–2014 was primarily controlled by a strong cyclonic flow anomaly associated with CP-type El Niño. The change of dominant environmental controlling parameter is ultimately caused by the change of ENSO behavior. Compared to the first interdecadal period, a stronger EP-type ENSO variability in  1977–1998 leads to a stronger circulation and SST response in ENSO decaying phase. The occurrence of more frequent CP type El Niño in  1999–2014 was possibly attributed to both suppressed convection and low-level divergence over the central equatorial Pacific and a warming trend in the tropics.