Western South China Tropical Cyclone Monitoring And Forecasting Of Heavy Precipitation Method

The eastern and southern China is one of the main regions where suffer severe influence oftropical cyclones in the world. Therefore, the heavy rainfall and other severe weather caused bythe landing tropical cyclones often bring extreme disasters for the people and society economy.Southern China especially Guangxi province, is a major region of the areas. According to thestatistic analysis of the Guangxi observatory, there are 2.2 tropical cyclones moving into thisprovince every year averagely, and 70% of heavy rainfall was caused by the landing tropicalcyclones or the interaction between the tropical cyclones and other environmental systems. In this paper, all the tropical cyclones which influenced Guangxi province occurred inthree years from 2001 to 2003, such as the numbers of 0103,0104,0107,0212,0214,0218,0220,0307,0313, and the 0510 which landed at Guangdong in 2005 are selected as objects forstudy. The characteristics and the mechanism of the heavy rainfall caused by landing tropicalcyclones are analysed in detail, using the information from The Tropical Cyclone Annual andWebsite of China Typhoon, precipitation data, NCEP/NCAR reanalysis data, GMS-5Black-body temperature (TBB), the retrieved data from NOAA-16 AMSU, moisture profile incloud field and TBB from FY-2C. Based on the study, methods for diagnosing and forecastingthe intensity and distribution of precipitation in 24h, 6h and 3h over Guangxi province aredeveloped. In the first part of this study, developing the method for forecasting rainfall in 24hmeans to reveal the characteristics of environmental field factors in the synoptic scale as thebackground before heavy rainfall occurred. First at all, daily rainfall within the 7 tropicalcyclones of 2001 and 2002 are analyzed and divided into three types: zonal, meridional andNE~SW orientated kinds. Then, the detail analyses on the main meteorological factors atupper-level, middle-level and low-level related to the heavy rainfall in each type are made andtry to find the relationship between the rainfall in future 24h and each factor. The resultindicates that when tropical cyclones landed in South China and moved into Guangxi province,the rainfall distribution and intensity in 24h relate close to the meteorological factors such asthe streamline field at upper level, the subtropical high at middle level, the low-level jet, thelow-level wind shear, the moisture flux convergence, the monsoon cloud surge and so on. Onthe other hand, the different allocation of these factors forms different type of rainfalldistribution and precipitation intensity. According to the relationship between the large-scaleenvironmental characteristics and rainfall field, the conceptual models of 24h precipitation aresummarized.In the second part, the movements of mesoscale convective system are tracked with 6hinterval data. As the first part, 6h rainfall amount of Guangxi province occurring in the 9tropical cyclones are divided into four types: zonal, meridional, NE~SW and NW~SEorientated kinds and detail analyses of their characteristics of the main physical factors atupper-level, mid-level and low-level in each type are finished. The result shows that the rainfalldistribution and intensity in 6h relate close to the physical factors such as divergence field atupper-level, the field of vorticity at mid-level, convergence and ascending motion and thelow-level jet, the moisture flux convergence and so on. With this understanding, the conceptualmodels of 6h precipitation forcasting are summarized.In the third part, the evolution of cloud system and the movements of cold and warm airare taken as the main factors for 3h precipitation prediction in Guangxi province. Firstly,analyze the barometric evolution in the past 3h, the structure of cloud system and the variety ofmesoscale cloud cluster at the zone where TBB≤-52oC region and find out the string ΔTBBgradient area in ΔTBB≤-25oC. Secondly, infer the route of tropical cyclone and thedevelopment of cloud system in the next 3h. Finally, deduce the intensity and distribution ofprecipitation in the next 3h. Based on the results above and the four kinds of tropical cycloneroute which influence Guangxi province, the main characteristics of the four kinds of route areabstract, and the conceptual models are produced.In the last part of this paper, the tropical cyclone 0510 landed at Guangdong province in2005 is selected as case study. Its thermal structure, environmental factors, physical factors, theintensity and distribution of precipitation are analyzed in detail and compared them with theconceptual models in the first two parts to verify the conceptual models.