广西热带气旋 6 h 降水天气概略模型及其应用
The Synoptic Conceptual Model of 6-hour Tropical Cyclone Rainfall and Its Application in Guangxi
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摘要: 选取 2001, 2002 年和 2003 年登陆华南西部的 9 个热带气旋(TC), 运用广西 89 站每 6 h 雨量资料、NCEP/NCAR 格点资料以及卫星云图, 分析 TC 登陆华南西部前后广西 6 h 强降水的物理量场特征。 经普查分析将 TC 造成的降水区划分为纬向型、经向型、NE—SW 向型和 NW—SE 向型 4 种; 在对各型高、中、低层主要因子详细分析的基础上, 概括归纳出了这些降水型各自前 6 h 的物理量场特征概略模型图及各降水型的主要转化趋势, 对其强降水形成机理尽可能地给出了解释, 并给出降水区及降水强度的确定方法, 可以为 TC 登陆华南西部前后广西区降水临近预报提供某种参考。Abstract: Every 6-hour rainfalls of 9 tropical cyclones (TC) that influence Guangxi Autonomous Region in three years from 2001 to 2003 with the number of 0103, 0104, 0107, 0212, 0214, 0218, 0220, 0307 and 0313 are selected for the study. The characteristics and the mechanism of the heavy rainfall caused by landing tropical cyclones are analyzed in detail, using the information from Tropical Cyclone Annual, observational precipitation data, NCEP/NCAR reanalysis data and black-body temperature (TBB). Based on the study, methods for diagnosing and forecasting the intensity and distribution of precipitation in 6-hour over Guangxi are developed.Every 6-hour rainfalls within the 9 tropical cyclones are analyzed. The regions with 6-hour rainfall amount over 5 mm are picked up, especially those areas of over 50 mm rainfall caused by TC are divided into four types: zonal, meridio nal, NE—SW and NW —SE orientated kinds. Then, the detailed analyses on the main physical factors at upper-level , middle-level and low-level related to the heavy rainfall in each type are made and the relationship between the rainfall in future 6-hour and each factor is investigated. The result shows that the rainfall distribution and intensity in 6-hour relate closely to the physical factors such as divergence field at upper-level, the field of vorticity at middle-level, convergence and ascending motion and the low-level jet, the moisture flux convergence and so on. On the other hand, different type of rainfall distribution and precipitation intensity is formed by the different allocation of these factors. With this understanding, the conceptual models of 6-hour precipitation forcasting and its main transforming direction are summarized. And the forcasting method on the rainfall distribution and intensity in 6-hour is presented. The method can be simply described as below. The location of TC center, the trend of low-level jet and the physical factors such as divergence field at upper-level, the field of vorticity at middle-level, convergence and ascending motion at low-level can help to find out the rainfall type. Then with the location of low-level jet, the distribution of TBB and the moisture flux convergence, themain area of rainfall can be fixed on. Finally, based on the results above and combined with the evolution of cloud systems, the allocation of physical factors and the negative variate zone of TBB, the intensity of precipitation can be worked out.The method is tested on two TCs in 2006. The test results indicate that the false fo recasts are made up of more false-alarm than miss, and the fo recasting of heavy rainfall is not so good .
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Key words:
- tropical cyclone(TC);
- heavy rainfall;
- physical factor;
- conceptual model
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表 1 TC每 6 h 降水区型的转换过程
Table 1 The converted process of 6 h TC precipitation types
表 2 低空急流与降水型的对应关系
Table 2 Relationship between low-level jet and precipitation types
表 3 200 hPa 辐散区走向与降水型出现次数的对应关系
Table 3 Relationship between 200 hPa divergence field and precipitation types
表 4 700 hPa 上升运动区走向与降水型出现次数的对应关系
Table 4 Relationship between 700 hPa ascending motion and precipitation types
表 5 500 hPa 正涡度区走向与降水型出现次数的对应关系
Table 5 Relationship between 500 hPa vorticity field and precipitation types
表 6 降水型的确定要素
Table 6 Main factors of each rainfall type
表 7 降水强度的确定要素
Table 7 Main factors about the rainfall intensity
表 8 2006年8月第6号TC广西 6 h 降水预报结果检验
Table 8 Precipitation forecasting test result of TC NO.6 in Auguest, 2006
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