| By using a variety of remote sensing data such as TRMM satellite precipitation data and JTWC best track data and combining with Sverdrup theory and Goldbrough-Stommel large-scale circulation vorticity constraint theory,the spatial structure of precipitation induced by typhoon in South China Sea?SCS?from 2001 to2016 was statistically analyzed,the mechanism of this spatial distribution was clarified,and its influence on the upper circulation in the south China sea was further elaborated in this paper.The SCS has a unique geographical location,which is located in the east Asian monsoon region.It is adjacent to the northwest Pacific Ocean,which has the most typhoons in the world,and typhoons also generated in the local region,so the SCS is deeply affected by typhoons.The typhoon precipitation in SCS shows a significant asymmetric characteristic in space,which is"left-biased".Under the influence of monsoon,its spatial distribution in winter and summer is different:in summer,the maximum of typhoon precipitation is located on the left side of the moving direction of typhoons,while it appears on the front side in winter.Further analysis shows that the spatial morphology difference is mainly caused by the distribution difference of weak typhoon precipitation.The average rainfall rate is related to season,typhoon intensity,the translation speed and direction of typhoon.Typhoon intensity and its movement have certain influence on the spatial distribution of typhoon precipitation.Typhoon is a kind of meteorological disaster that occurs on the sea—air interface.The results show that:?1?Typhoon precipitation is related to relative humidity,vertical velocity and sea surface temperature anomalies?SSTA?.In summer,the higher the relative humidity in the lower troposphere,the more intense the vertical upward movement(??27?0),and the smaller the change of SST,the higher the average rainfall rate of typhoons.They also contribute to the spatial asymmetry of typhoon precipitation during summer in SCS.?2?The spatial asymmetry of typhoon precipitation is related to the combined action of the direction of vertical wind shear?VWS?and the heading of typhoon.When the VWS direction is to the left?right?of the typhoon moving direction,the maximum typhoon precipitation is to the left?right?of the typhoon moving direction.The reason for the difference of spatial distribution of typhoon precipitation in summer and winter is that the different probability of the relative position of VWS direction and typhoon moving direction.In addition to the spatial structure of typhoon precipitation,the contribution of typhoon in summer?from June to September?to the precipitation,freshwater flux and its possible influence on circulation anomalies in SCS were also studied in this paper.The main conclusions are as follows:?1?Typhoon is one of crucial factors that impact the precipitation in northern and middle South China Sea,and the daily mean precipitation can increase 12mm,which accounts for a half of the daily mean rainfall in SCS during summer.Besides,there are significant differences in location and intensity of the rainfall distributions between Northwest Pacific Ocean typhoons?NWP TYs?and South China Sea typhoons?SCS TYs?.?2?In summer,the saline circulation in SCS induced by freshwater flux shows a weak cyclone that centers on the southwestern part of Hainan island with its magnitude is about–0.15Sv,which occupy approximately 10%of wind-induced circulation?about–1.5Sv?during the corresponding period.?3?Precipitation induced by typhoon can intensify cyclonic saline circulation in the north-central part of the SCS in summer.And the intensity of saline circulation caused by NWP typhoons is stronger compared to SCS typhoons. |
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