A Study On The Related Charateristics Of Regional And Circulational Dynamic For The Unusual-turning TCs Over The Western North Pacific

Despite great improvements have been made in forcasting tropical cyclone(TC)tracks for the past few decades,the unusual tracks of TC are not well predicted at present.In this study,K-means cluster method is applied to classify unusual turning locations of TCs over the western North Pacific from 1949 to 2016,the temporal and spatial charateristics are preformed for the different clusters.Afterwards unusual north-turning and west-turning tracks of TCs in high-frequent areas of unusual-turns are chosen to do dynamic composition analysis.After that,vector empirical orthogonal function(VEOF)is performed to subdivide the composites as well as different wind patterns effectively.Finaly,two TCs which belong to the main models of unusual TCs,named nock-ten with north-turning and Orma with west-turing around Taiwan Island,are chosen to investigate unusual tracks,then methods are attemped to identify the unusual-turning points of two TCs.The temporal and spatial distribution charateristics of unusual-turning TCs are studied.Analysis results show that it is siginificantly different for the distribution of frequencies of unusual-turning TCs.Differences manifest in the different regions for the occurrences of unusual turning TCs,while mainly occur in warmer summertime around higher latitude area,and mainly occur in autumn around the lower latitude area.There are obvious periods of 2-4 years?3-6 years for the unusual turning TCs,variability shows that they are ascended before Mid-1980 s,while declined after that time.And the annual variation in the lower latitude region is more similar to the total,but there are no obvious features existing in the higher latitude.Compositions results for unusual north-turning and west-turning TCs reveal that durning the unusual turning time,the enhancement of continental subtropical high and western North Pacific subtropical high effect the west-turning tracks,while compared with the west-turning tracks,main environmental systems influence the north-turning tracks include the western North Pacific subtropical high which is weakened and eastward withdrawing and the westly trough which is strengthened,Additionally,the results of the low-level(850hPa)show that in the sortheast direction of TCs,a anticyclone circulation orientates for the unusual norh-turning tracks while a cyclone circulation exits for the unusual west-turning tracks.Additionally,VEOF analysis for the circulation of unusual north-turning TCs show that four VEOFs satisfy Noth's rule of thumb and two VEOFs of west-turning TCs satisfy it.VEOF-1 of unusual north turning TCs represent TCs are mainly located in the sorthward of western North Pacific subtropical high and before the westly trough,the composite tracks manifestate from westnorthward to northward,eastward finally.VEOF-2 pattern indicates that there are two anticyclone systems in the eastnorthward and eastsouthward of TCs,which is mainly in the South Ses of China and tracks are unusually from west to north.The weakened and eastward withdrawing of western North Pacific subtropical high mainly appear in VEOF-3 pattern while the two anticyclones locate between the TC in VEOF-4 model,and their tracks are mainly from westnorthward to northward.For the unusual west-turning TCs,VEOF-1 model indicates that continental subtropical high and western North Pacific subtropical high influence their tracks respectively.VEOF-2 model mainly performs that two anticyclone locate northward of TCs.North-turning TC “nock-ten” and west-turning TC “Orma”,which are belong to the main models around Taiwan Island is selected to do the analyses of the circulations,it is found that the circulation fields of “nock-ten” and “Orma” are closed related to the main models of VEOF.Furtherly,stream function and potential function are used to figure out the divergent wind and rotational wind,results reveals that at 200 hPa,a divergent band may has close relation to north-turning nock-ten,while the west-turning Orma dosen't reveals it.Moreoverly,the extensional beta-advection models are applied to identify TCs of main models.Results show that the north-turning nock-ten track can be forecasted well when considering the climatic-flow and anomalous flows,however the west-turning Orma forecast well considering the anomalous flows.