The Modulation Of Tropical Cyclone Genesis Over The South China Sea And Western North Pacific By The Madden-Julian Oscillation Under Different ENSO Conditions

This paper explores the Madden-Julian Oscillation(MJO)modulation of tropical cyclone(TC;hereafter,MJO-TC)genesis over the South China Sea(SCS)and Western North Pacific(WNP)under different El Ni?o-Southern Oscillation(ENSO)conditions.Analyses used Joint Typhoon Warning Center(JTWC)Best Track data,the Real-Time Multivariate MJO(RMM)index,and European Center for Medium-Range Weather Forecasts(ECMWF)Interim(ERA-Interim)reanalysis data.The results showed that the MJO has significant modulation on both the SCS and WNP TC genesis in neutral years,with more(fewer)TCs forming during the active(inactive)MJO phases.However,during the El Ni?o and La Ni?a years,the MJO-TC genesis modulation over the two regions differs from each other.Over the SCS,the MJO modulation of TC genesis is stronger in the La Ni?a years,while it becomes weaker in the El Ni?o years.Over the WNP,the MJO has a stronger influence on TC genesis in the El Ni?o years compared to that in the La Ni?a years.Related Genesis Potential Index(GPI)analysis suggests that midlevel moisture is the primary factor and vorticity is the secondary factor,for the strongest MJO-TC genesis modulation over the SCS in the La Ni?a years.Over the WNP,midlevel moisture is the dominant factor for the strongest MJO-TC genesis modulation during the El Ni?o years.These results can be explained by increased water vapor transport from the Bay of Bengal,associated with enhanced westerly wind anomalies,during the active phases relative to the inactive MJO phases;these conditions prevail over the SCS during the La Ni?a years,and over the WNP during the El Ni?o years.