Study On Characteristics Of The Western North Pacific Tropical Cyclone Types And Its Potential Impact Evaluation

Tropical cyclones(TCs)are extreme destructive natural weather systems.They often trigger gale,storm rainfall and storm surge along their tracks,leading to enormous losses of lives and properties in many countries.In the past decades,with the rapid development of social economy,the impact of TCs has a trend of increasing dramatically.Therefore,analysis of the TCs activity features and evaluation of its impact have considerable practical significance.In the dissertation,taking the western North Pacific(WNP)TCs over the period 1949~2013 as the object of study,characteristics of the WNP TCs and its potential impact evaluation are discussed.The major research contents and conclusions are as follows.Firstly,the tracks of the WNP TCs are classified by K-means clustering algorithm and characteristics of the WNP TCs genesis location and trajectory in each cluster are discussed.The results show that:(1)The WNP TCs tracks are classified into straight-moving patterns(including cluster?and cluster?,accounting for 60%)and recurving patterns(including cluster ?,cluster ? and cluster ?).(2)Most of the straight-moving types land in the coast areas of China and the north central of the Philippines.The recurving types,with the steer positions mainly concentrating on the regions of(120°E~170°E,10°N~30°N),are numerously prone to Korean Peninsula and Japan.(3)ENSO(El Ni?o–Southern Oscillation)events have an influence on the genesis location and trajectory of the WNP TCs.Secondly,the spatiotemporal characteristics of the WNP TCs in each cluster and the impact of the ENSO events are analyzed.The results show that the characteristics of the WNP TCs are as follows.(1)Activity period of all the WNP TCs range from July to October(accounting for 68.88%),in which they reach the peak in August(7.34 monthly).(2)The average frequency of the WNP TCs(33.2)takes on a declining trend,particularly an obvious reducing tendency after the 1990 s.Cluster?has the largest average frequency(15.5).(3)The average intensity(35.41m/s)presents a weakening tendency,with a remarkable descending trend before the 1980 s and tending to stability after that(34.25m/s).Cluster ? has the strongest average intensity(53.52m/s).(4)The average lifespan(6.57d)shows a small amplitude change trend with increasing at first and then decreasing,and they achieve the maximum value(6.67d)during the 1980s~2000s.The distribution of the WNP TCs lifespan is consistent with the intensity in each cluster.On the whole,the spatiotemporal variation characteristics of the WNP TCs are subjected to effect of the ENSO events.Last,based on power dissipation index(PDI),the potential impact of the WNP TCs is evaluated.The study areas are divided into 2°×2° lat./long.grid in this evaluation method.Then in accordance with the inter-decadal grid PDI values of the total WNP TCs,the inter-decadal times of recorded locations of the WNP TCs tracks and the relevant comparative times of recorded locations in single grid accumulated proposed,six potential impact grades are built by the three parameters,including extra-high,high,medium-high,medium,medium-low and low grade.The results show that:(1)The WNP TCs in the zone of(100°E~140°E,6°N~30°N),with the strongest impact degree,are mainly medium and above potential impact grades.South China and East China are mainly dominated by medium-low and low potential impact grades,and the impact grades present a strengthening trend in East China.(2)The impact degree of cluster?and cluster ? show a tendency of declining.The impact regions of cluster ? and cluster ?develop towards low latitudes and eastern areas of the WNP,and cluster ? presents a trend of the eastern districts in the WNP.