一次典型梅雨锋锋面结构分析

THE STRUCTURE ANALYSIS OF A TYPICAL MEIYU FRONT

中文关键词:  梅雨锋  梅雨赤道锋  多重锋面  梅雨锋概念模型

英文关键词:Meiyu front  Meiyu equatorial front  Multilayer fronts  Conceptual model of Meiyu front

中文摘要:

      1999年梅雨期在长江中下游维持着一条典型的梅雨锋,锋面和梅雨雨带呈东西走向,从中国的四川省一直延伸到日本。锋面两侧的温度及湿度对比明显,并且其上有数个中间尺度的低涡沿梅雨锋依次向东移动发展,在长江中下游造成严重的梅雨暴雨和洪涝。文中分析了1999年这次典型梅雨锋的锋面结构。结果表明,从温度场看,由于梅雨区对流和降水的显著发展,梅雨锋的低层温度对比几近消失,其中上部仍具有典型的上宽下窄的锋面结构,锋面随高度向北倾斜。在低层经向温度场呈现复杂的暖-冷-暖的结构,即北部华北平原为地面感热加热造成的相对较暖的变性极地大陆气团,中间为冷空气南下和降水冷却造成的相对较冷的梅雨区,南部是相对较暖的热带海洋气团。在这种温度场下,由北部低层变性暖气团与梅雨区偏冷空气形成了明显的温度对比区,文中定义这个区域为梅雨赤道锋。因而,在低层东亚梅雨区的锋区结构由梅雨赤道锋和减弱的梅雨锋构成。在600hPa以上前者消失,只有单一的极锋型的梅雨锋结构。在此分析的基础上文中给出了东亚梅雨期锋面结构模型图。另外还指出,从假相当位温场分析,主要表现出梅雨区的深厚对流。降雨引起了高θ_se带及其南北高θ_se梯度区,其北侧高θ_se梯度区大致相当于梅雨锋,而南侧高θ_se梯度区则不是典型意义下的梅雨锋锋面。

英文摘要:

      There existed a typical Meiyu front along the mid-lower Yangtze Basins during Meiyu period in 1999. The Meiyu front and rain belt extended eastward from Sichuan Province to Japan. Along the Meiyu front, there was a sharp contrast of temperature and hum idity. What's more, a few mesoscele vortexes moveed to the east along the Meiyu front, which produced severe rainstorms and floods in mid-lower Yangtze Basins. The results reveal that there is almost not emperature contrast in the lower level of Meiyu front because of the highly development of convection and rain. But it owns the typical Meiyu front structure at the upper level. In the lower level, the structure of meridional temperature likes "sandwich", for the relative low temperature in the Meiyu rain realm, and the relative high temperature along the other two sides. Under this condition, there forms a sharp temperature contrast belt between the cold air mass of Meiyu region and the relative warm air mass of the north land. Following the definition of Equatorial Front defined by Xie Yibing, we define this belt as Meiyu Equatorial Front. So the East-Asia Meiyu front system includes Meiyu Equatorial Front and Meiyu front under 600 hPa, but there is only Meiyu front above 600 hPa. To illustrate this structure more clearly, we provide an East-Asia front structure model.