| Rainstorms caused by landfalling typhoons in China often lead to secondary hazards such as floods,landslides and debris flows,having huge impacts on human society.It plays a decisive role in basis of decision making and risk aversion through the statistical analysis of the precipitation distribution characteristics and the influencing factors of landfalling typhoons.In this paper,based on the precipitation data with spatial and temporal resolution of 1h and 0.1°,the landfalling typhoons（LTC）selected from 2008 to 2020 are clustered into two categories:LTC1 and LTC2 according to different landing points and landing tracks.They are further classified into strong landfalling typhoons（SLTC1,SLTC2）and weak landfalling typhoons（WLTC1,WLTC2）according to the intensity stage while making landfall,and the evolution law of landfalling typhoon precipitation under different classification can be explored.Landfalling typhoons of shifting tracks with different intensities also lead to significantly different precipitation characteristics.The primary rainfall areas affected by SLTC1 are Jiangsu,Zhejiang,Fujian,southern Jiangxi and vicinity of the Dabie Mountain in Anhui Province.The extreme rainfall locates in inner rainbands,and the rainfall tends to weaken at first and then amplify before landfall,whereas it decreases slowly after landfall.In the meantime,the strong precipitation area shifts from southeast to northwest,and then to the northeast quadrant.The inner!"#and$%&of SLTC1 intensifies rapidly during-6h–0h.While the intermediate!"#decreases during-24h–18h attributed to the diminished$%&(’!（&）during-24h–-12h（-12h–18h）.The rainfall caused by WLTC1 in Zhejiang Province is much lighter than SLTC1,and the heavy rainfall distribution is more asymmetric relative to TC center,mainly located in the southern part of the inner and intermediate rainbands.Besides,the precipitation associated with WLTC1 increases gradually before landfall and decreases rapidly after landfall,with most rainfall located in the south of WLTC1.The inner!"#and$%&are much weaker than that of SLTC1 during 0h–6h,wheras the$%&is stronger than that of SLTC1.The intermediate!"#and$%&present distinct enhancement tendency before landfall.Landfalling typhoons of westward tracks with different intensities lead to significantly different precipitation characteristics.The main areas influenced by SLTC2 precipitation are southern Guangxi,southwestern and eastern Guangdong,southwestern Fujian,Hainan Province and Leizhou Peninsula.The range of heavy precipitation is wester and larger than that of WLTC2,and the rainfall distribution in the east-west direction is more symmetrical.The extreme value of precipitation falls in the whole internal rain belt and the southern moderate rain belt.The inner average rainfall intensity（!"#）and rainfall coverage(’!（&）tends to increase before landfall,while the inner conditional rainfall intensity($%&)decreases rapidly.The intermediate$%&decreases（increases）in the periods of-6h–0h（0h–6h）,while the outer’!(（&）decreases rapidly during 6h–12h.The heavy rainfall caused by WLTC2 mainly locates in the western coastal area of the Pearl River Estuary with small range,but the rainfall in the southern Jiangxi Province,the central and western Fujian Province is heavier than that of SLTC2.At the same time,the extreme rainfall area in Hainan Province is northwester than that of SLTC2.The heavy rainfall areas of the inner,middle,or outer rain bands all fall in the southwest quadrant and the rainfall coverage is small.The inner!"#and$%&increase rapidly before landfall and decrease slowly after landfall,and the inner’!(（&）decreases rapidly after landfall,which is markedly different from that of SLTC2.While the intermediate$%&shows similar tendency with SLTC2,and the amplification is even larger than that of SLTC2during 0h–6h,whereas the outer’!(（&）shows opposite tendency.Diurnal variations of typhoon rainfall show significant contrasts between the four classification.The diurnal peak of!"#over the ocean in SLTC1 corresponds to the trough in WLTC1.The diurnal variation amplitude of!"#and$%&in the inner region over the ocean in WLTC1 is larger than that in SLTC1,and the rainfall area in WLTC1 over the ocean shrinks in the evening.The diurnal peak of!"#over the land in the inner（outer）region occurs in the morning（afternoon）in SLTC1.The diurnal peaks of!"#and’!(（&）of SLTC2 occur in the afternoon（15 LT）over the land,and the diurnal variation amplitude of’!(（&）in the intermediate and outer region is significantly larger than that of WLTC2 over the land.The!"#of SLTC2 in the inner and intermediate region over the ocean shows opposite diurnal variation to that of WLTC2 in the evening.Meanwhile,they share distinct diurnal variation of the!"#in the intermediate and outer region over the land.The$%&of LTC2 over the ocean displays an enhancement pattern at night,while LTC1 does not show a similar feature.The primary weather systems and mechanisms modulating the precipitation distribution before and after landfall of SLTC1,WLTC1,SLTC2 and WLTC2 are explored by composite analysis.The results show that LTC1 and LTC2 display distinct difference in the location of the South Asia High（SAH）,the magnitude and direction of VWS and the distribution of low-level moisture convergence.The moisture transport channel to the north of SLTC1 through the easterly flow along the southern edge of the subtropical high is not found in the composite analysis of WLTC1.The position of subtropical high at 500 h Pa and the whole atmosphere precipitable water（PW）are different between SLTC2 and WLTC2.LTC1 and LTC2 also display diverse instability conditions and vertical structures（including the warm core structure,the ascending motions in different radius and the asymmetric distribution of convergence）.Through the comparative analysis of several typical cases,statistical results are verified to be credible.Moreover,the distribution characteristics of spiral rainbands and the evolution mechanism of dynamic and thermal structures are investigated,according to the WRF high-resolution numerical model data during the landing process of Soudelor（2015）and Matmo（2014）.The other comparative analysis indicate even in the same classification,the associated precipitation distribution may be quite different,but they can also brought quite various heavy rainfall.It indicates that due to the uniqueness and complexity of landfalling typhoons,even for typhoons under the same classification of similar tracks and intensities,the precipitation distributions can be quite different.Thus it is necessary to recognize the key impact mechanism which modulates landfalling typhoon rainfall. |
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