Impacts Of Tropical North Atlantic SST On Western North Pacific Landfalling Tropical Cyclone Frequency

Using the Regional Specialized Meteorological Center Tokyo–Typhoon Center(RSMC Tokyo),China Meteorological Administration(CMA),Joint Typhoon Warning Center(JTWC)best-track data during 1977-2017,1:4000000-scale geological map obtained from the National Geomatics Center of China(NGCC),Extended Reconstructed Sea Surface Temperature(ERSST)version 4 dataset,National Centers for Environmental Prediction(NCEP)–National Center for Atmospheric Research(NCAR)reanalysis data,Global Precipitation Climatology Project(GPCP)precipitation data this study analysed the correlation between the tropical North Atlantic(TNA)sea surface temperature anomaly(SSTA)in different seasons from 1977 to 2017 and the frequency of landfalling tropical cyclone(TC)in the western North Pacific(WNP)in summer and autumn,and the distribution characteristics of the WNP atmosphere circulation anomalies under its influence with statistical analysis and numerical simulations.The purpose is to explore the form and possible mechanism of TNA SSTA affecting WNP lanfallding TC frequency.Results show that:(1)During 1977-2016 TNA SSTA has significant negative correlations with the frequency of TC making landfall in China,Vietnam,the Korean Peninsula and Japan,and the entirety of East Asia in summer and autumn.TNA SSTA influences the frequency of TC landfalls in these regions by regulating TC genesis location and frequency associated with modulated environmental conditions.During cold TNA SST years,larger low-level relative vorticity and weaker vertical wind shear lead to more TC formations over the South China Sea(SCS)and western Philippine Sea(WPS),and larger low-level relative vorticity,higher midlevel relative humidity,and weaker vertical wind shear result in more TC formations over the eastern part of WNP(EWNP).More TCs forming over different regions are important for more TC landfalls in Vietnam(mainly forming over the SCS and WPS),south China(predominantly forming over the SCS),Taiwan(mostly forming over the WPS),and the Korean Peninsula and Japan(forming over the WPS and EWNP).Tracks of these landfalling TC basically follow the mean steering flow in spite of different directions of steering flow anomalies in the vicinity.The modulation of large-scale environments by TNA SSTA may be through two possible pathways proposed in previous studies: the Indian Ocean relaying effect and the subtropical eastern Pacific relaying effect.(2)During 1979-2017 there is a significant positive association between TNA SSTA during spring and frequency of intense landfalling typhoon in China during autumn.Observational analyses show that warm SSTAs located in the TNA during winter can induce warm SSTAs in the western part of the western North Pacific(WNP)in subsequent autumn,through Rossby-wave response,wind-evaporation feedback,and warm water advection.The warm SSTA and associated higher mid-level humidity in the western part of WNP are responsible for the genesis and intensification of intense TCs in situ.