Investigation Of Asymmetric Structure Of Landfalling Tropical Cyclone Wind And Rainfall In China Based On Multi-source Merged Data

Landfalling Tropical cyclone is one of the most destructive weather systems to the coastal areas of China.Recent studies have approved that there exist an obvious asymmetric structure in landfall TC as that of in open seas,which related to Vertical Wind Shear(VWS),TC motion and underlying surface.The asymmetric distribution of wind and rainfall in Landfalling TC is one of the frontier scientific subjects and forecasting difficulties.Based on two sets of Multi-source merged data,MTCSWA and CMAPS,both the winds and rainfall asymmetric structure change and evolution have been discussed by 74 landfall TCs and 26 TCs respectively.The objective asymmetric indexes for wind and rainfall have been given to discuss the timely evolution.By observational analysis and numerical study,the possible physical reason to the amplification of inner-core rain-rate of typical Landfalling TC(LEKIMA)and also the intensification of asymmetric convection has been further discussed.Among those Landfalling TCs,71% of them exhibit maximum wind to the right of track,which has been defined as ROT wind structure.and 29% others show a LOT(Left of Track)distribution.The asymmetric index of ROT is closed related to its intensity.The Radius of Maximum Wind(RMW)of ROT is smaller than that of LOT,with stronger ROT than LOT.It has also showed that the monsoon background and basin difference could also change the distribution of RMW profiles.TC with intensity lower than STS(Strong Tropical Storm)and lower motion speed would refer to bigger RMW.The asymmetric index show the amplification of asymmetric wind after landfall.By disintegrated the TC rainfall during landfall process into axisymmetric component and asymmetric component,two parameters have been given to define the asymmetric content of rainfall.It has been shown that the asymmetric rain rate is closely related to TC intensity.Based on composited results,the inner-core rain rate has experienced an extensive outburst during few hours after landfall,the azimuth mean rainfall reach a maximum within 6hr after landfall correspondingly.The asymmetric content of rainfall is mostly contributed by the wave-1 asymmetric component.Both TC made landfall in mainland or over islands(including Taiwan Island and Hainan Island)have shown that intensification in inner-core rain rate,only the trends and corresponding periods differed.In strong VWS environment,the maximum asymmetric rainfall exhibited to the down shear-left(DL)side of TC.If the angel between TC motion and coastline is nearly vertical,the asymmetric rainfall is exhibited at the frontal(F)and right(R)side to TC motion.The observation investigation and numerical studies shown that during the landfall process of Super Typhoon LEKIMA,the wind exhibit a typical ROT asymmetric structure,however it has a more symmetric inner-core before landfall.The northward deep convection inside the RMW show an obvious intensification after landfall,which might be related to the growth of local instability caused by the landmass.Both the rainfall range and rain-rate exhibited three episodes of amplifications,with the first episode of intensification related to inner-core rain rate outburst.The inner rain bands and outer rain bands has different propagation characteristics.If a TC is in weak VWS(<5m/s)condition and its motion direction is nearly vertical to the coastline,than the asymmetric rainfall is to the frontal(F)and right(R)side towards its moving.