超强台风“桑美”(2006)近海急剧增强过程数值模拟试验

Numerical Simulation of Rapid Intensification Change of Super Typhoon Saomai(2006) over the Coastal Water of China

应用PSU/NCAR非静力平衡中尺度模式MM5(V3.5)设计试验方案,对超强台风"桑美"(2006)在我国近海的急剧增强和减弱过程进行数值模拟研究,模式较好地再现了台风的路径和强度变化;通过地形敏感性试验,着重研究了地形对近海台风强度变化的影响。结果表明:(1)"桑美"强度变化与南亚高压、副热带高压的强度变化呈反相变化关系,当南亚高压和副热带高压减弱时,台风急剧增强;台风中心附近对流层高层辐散的增强导致"桑美"急剧增强,对流层中低层辐散的增强以及中层辐合的增大与"桑美"的减弱密切相关;来自海洋的暖湿气流是"桑美"发展的关键条件;低层气旋性涡旋并入台风环流是"桑美"近海急剧增强的重要原因。(2)凝结加热过程对"桑美"的近海维持和发展增强非常重要,尤其是对流层中上层凝结潜热的突然增强有利于台风在近海的急剧增强。(3)小范围地形对"桑美"在近海的强度和路径有一定影响,但作用相对较小,而且主要表现在台风登陆前后;大范围地形导致水平风场的非对称分布和台风中心附近垂直运动的异常,最终影响到台风的强度变化。

Super typhoon Saomai （2006）, which struck China in August 2006 as the most intense typhoon China had experienced in recent 50 years, is a typical rapid-intensification tropical cyclone over the coastal water of China, whose intensity is even stronger than hurricane Katrina （2005） which is the costliest and one of the deadliest hurricanes in the history of the United States. Saomai is estimated to have been responsible for nearly RMB 20 billion yuan in damage. It can be traced back to a tropical storm on 5 August. The system strengthened into typhoon 2 days later and rapidly intensified into super typhoon over the coastal water of China on 9 August as the central pressure fell to 920 hPa. It then maintained its peak intensity for about 18 h before beginning to weaken. Saomai tracked into Zhejiang Province in the afternoon on 10 August, making landfall in Cangnan County and then rapidly weakened. Taking super typhoon Saomai as an example, a case numerical simulation study is made for different developing stages by the use of non-hydrostatic version 3. 5 of the fifth-generation Pennsylvania State University-National Center for Atmospheric Research （PSU-NCAR） Mesoscale Model （MM5） . The model can well simulate the track and intensity of typhoon Saomai, and can basically capture the characteristics of intensity change of Saomai, especially its intensification over the coastal water of China. The results show that the intensity change of Saomai is in inverse proportion to that of the South Asia high and the subtropical high, the South Asia high and the subtropical high decay in the typhoon rapid intensification stage. There is a favorable environment for typhoon intensification, such as strong divergence at the upper level, sufficient water vapor transportation and the merge of adjacent vorticity lumps. And the addition of divergence at the low-middle layer and convergence at the middle layer are associated with typhoon weakening. There is a direct relationship between the condensation latent heat and intensity of typhoon Saomai, the enhancement of the latent heat in the mid-upper troposphere is favorable to Saomai＇s intensification. The sensitivity experiments of orographic effect are carried on to study their effects on the change of intensity and structure of Saomai by keeping/removing mountains in the eastern area of Zhejiang and Fujian provinces. Contrast experiments demonstrate that small terrain has a little impact on track or intensity change of Saomai, but a large one plays an important role. Exactly, the general circulation would be changed by a large terrain.