强台风"云娜"登陆过程的研究——基于AREM模式的数值分析

使用新改进的双重嵌套AREM数值预报模式,并与高时空分辨率的探测资料相结合,针对台风“云娜”登陆加强的特点进行数值模拟分析,结果表明该模式对“云娜”台风环流特征、强度变化趋势和台风降雨等都有较强的预报能力。在此基础上,定量研究其登陆加强过程中三维大气中尺度场动、热力特征及演变过程,并探讨了其登陆加强的机理。由此得出了与“云娜”登陆加强相关的重要影响因子:(1)副热带高压西南侧的偏东引导气流加强是“云娜”登陆前移速加快、强度增强的有利环境场条件。(2)“云娜”近海移速加快时有较强的东密西疏的不对称流场结构,特别是其垂直速度场以及强对流发展的水平分布的强不对称特征与该气旋登陆加强同时发生,也可能与台风强度维持和加强存在一定的相关。(3)在“云娜”中心西南侧的强凝结潜热释放过程,有可能助其在登陆时加强。此外,在“云娜”发展加强阶段,低层暖湿、中层干冷的位势不稳定层结,有利于对流的强盛发展。(4)“云娜”登陆前后有强低空急流与之联结,并有垂直对流运动发展,由此可获得不断增强的潜热能量是其登陆加强的另一个重要机制。

THE NUMERICAL RESEARCH OF THE PRIMARY MECHANISM OF THE OFFING REINFORCEMENT OF TYPHOON RANANIM BASED ON AREM

The intensification process and mechanism of typhoon Rananim after landfall are studied in this paper on the basis of the successful simulation of typhoon circulation,thermodynamic structure,intensity trend,and precipitation by the revised Advance Regional Eta-coordinate Model(AREM).Two mesh domains of the grid size of 37 km and 12 km were designed to simulate the synoptic scale environment and the storm-scale structure respectively.A Betts-Miller cumulus parameterization scheme and an explicit microphysics scheme were used simultaneously in addition to the non-local PBL parameterization.The model was initialized at 12:00 UTC 11th August 2004 with the NCEP/NCAR reanalysis data,and no bogus data was added.The results of the simulation show that the intensification of the easterly steering flow in the southwest side of the western Pacific subtropical high is a probably favorable environmental condition for Rananim to become intensified and to move faster shortly before and after its landfalling at the costal city of Wenling in Zhejiang province at 12:00 UTC 12th August 2004.The results also show the horizontally asymmetric structure of east-dense-west-sparse streamline,and especially asymmetric distributions of vertical motion and vigorous convections at about landfalling might be related to the maintenance and inteisification of Rananim.It was found that the heat release process of water vapor in the southwest side of the center of Rananim is likely benefial to its intensification,the potential unstable stratification of warm-wet in lower layer and dry-cold in the middle layer and the strong potential heat energy transportation by the low level jet are also in favor of the vigorous development of convections.The further study shows that the simulation of the sea-level pressure and surface winds of typhoon Rananim could be further improved if some bogus data and a coupled ocean and atmosphere model are incorporated.