一次热带气旋过程对出梅影响的数值模拟研究
投稿时间: 2016-07-14  最后修改时间: 2016-09-12  点此下载全文
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作者单位E-mail
朱哲 解放军理工大学气象海洋学院 zhuzhejl@sina.com 
钟中 解放军理工大学气象海洋学院 zhong_zhong@yeah.net 
卢伟 解放军理工大学气象海洋学院  
基金项目:国家自然科学基金项目(41430426);国家自然科学基金青年科学基金项目(41605072);江苏省自然科学基金青年基金项目(BK20160768)
中文摘要:本文利用中尺度数值模式WRF对2001年江淮梅雨期热带气旋(TC)进行数值模拟,研究“飞燕”对梅雨结束过程的影响。结果表明,模式能够较好地模拟出“飞燕”的路径与强度演变,并能够较好的再现梅雨后期的降水强度和落区。对比分析消除“飞燕”影响的敏感性数值试验结果发现,“飞燕”影响梅雨的机制在于伴随着其向东北向移动,西太平洋副热带高压北抬,东亚高低空急流强度均有所减弱,低空切变辐合变弱,梅雨锋强度减弱,使得来自西南方向的水汽输送减少,造成假相当位温梯度和湿位涡倾斜项减小,垂直上升运动明显削弱,降水中断,导致梅雨结束。而消除“飞燕”影响后,梅雨后期降水仍然较多,梅雨期将有所延长。
中文关键词:热带气旋  梅雨  相互作用  数值模拟
 
Numerical simulation study on the impact of a tropical cyclone on ending of Meiyu
Abstract:Meiyu and tropical cyclone (TC) in the northwestern Pacific are important factors of the weather and climate in the East Asia. Both of them play important roles in the rainfall in east China, especially during Meiyu period. A lot of statistical and synoptic analysis on the interaction between Meiyu and TC has been carried out. Previous studies have revealed that TCs might lead to the interruption of Meiyu, but less attention has been paid to the mechanism on such interruption effect. This work, as a case study, the impact of TC Chebi (0102) on the ending of the Meiyu in 2001 was investigated in terms of the sensitivity simulations with the limited-area numerical model. By use of the simulation output with and without the influence of Chebi, the effect of TC on the western Pacific subtropical high, moisture transport and pesudo-equivalent potential temperature are analyzed, which discloses the mechanism how Chebi exhibits its impact on the rainfall and the ending of the Meiyu. The Weather Research Forecasting model (WRFver3.4.1) is used in this study and the initial and boundary conditions are extracted from the National Centers for the Environment Prediction National Center for the Atmospheric Research (NCEP/NCAR) reanalysis data at 1°′1° resolution. The model domain is centered at (26°N, 121°E) with horizontal resolution of 20 km. The horizontal grid dimensions are 110′130. There are 27 levels in the vertical, and the top of the model is at 50 hPa. The model is initialized at 1200UTC 21 June 2001, and the integration ends at 1800UTC 25 June 2001. The time step is 60 s, and the results are output at 6h interval. The experiment with a bogus vortex via automatic vortex-following algorithm is marked as the control run (CTL). The simulation results show that the model can well reproduce the track and intensity variation of Chebi, as well as the distribution and intensity of the rainfall during the late Meiyu period. In addition, the sensitivity run (SEN) was also conducted through removing TC circulation from the initial fields, to investigate the response of the atmospheric circulation and rainfall when TC effect was not considered in the simulation during Meiyu period. Comparison studies for the influences with Chebi suggest that the mechanism of Chebi on Meiyu lies in, as Chebi moves northeastward, the low-level jet axis moves northward and become weaken above lower and middle reaches of Yangtze river, and the coupling between lower and upper level jets grows weak which makes a decreasing of Meiyu front and moisture transport from southwest region. Besides, the western Pacific subtropical high jumps northward and the water vapor are transported from southwest region to north of Huaihe river, which reduces the rainfall and makes the ending of Meiyu on June 25. Moreover, the weakening pesudo-equivalent potential temperature horizontal gradient and the horizontal component of moist potential vorticity associated the vertical velocity also make the interruption of Meiyu. On the other hand, without the influence of Chebi, the western Pacific subtropical high jumps late, the low-level and upper-level jets remain for a long time, and the low-level wind shear and convergence are preserved. Strong ascending flow from lower to upper levels provides a favorable dynamical condition for Meiyu and the coupling between lower and upper level jets is helpful for the enhancement of southwest wind at lower levels. At the same time, the gradient of pesudo-equivalent potential temperature and baroclinic instability are profitable to the increasing of vertical vorticity and occurrence of rainstorm, which results in the maintenance of rainfall in the late Meiyu period and makes a delay of the ending of Meiyu.
keywords:tropical cyclone  Meiyu  interaction  numerical simulation
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