Effect of ENSO phase on the contribution of environmental variables to tropical cyclone genesis in the western North Pacific

Changes in large-scale environmental variables between ENSO phases cause shifts in tropical cyclone (TC) features (genesis location and frequency) in the western North Pacific (WNP). This study examines the sensitivity of the interannual variation of TC genesis to individual environmental variables, including 600-hPa relative humidity (RH600), sea surface temperature (SST), 850-hPa relative vorticity (RV850), and vertical wind shear (VWS). An axisymmetric model was used to simulate TC genesis in 16 selected ENSO years during 1970-2015. The control experiment revealed that the axisymmetric model can capture a contrasting pattern of TC genesis between conventional ENSO phases in the northwest and southeast sectors of the WNP. The sensitivity experiments revealed that RH600 and RV850 play a dominant role in regulating ENSO-related TC genesis anomalies in the northwest and southeast sectors, respectively. Meanwhile SST and VWS have negligible impact on TC genesis anomalies.