基于海平面气压动力反演的台风涡旋初始化方法

A new approach to typhoon vortex initialization based on the dynamic retrieval of sea level pressure

中文关键词:  台风， QuikSCAT， 反演， 资料同化， 模式初始化

英文关键词:Typhoon, QuikSCAT, Retrieval, Data assimilation, Model initialization

中文摘要:

      提出了一种基于海平面气压动力反演和变分同化技术初始化数值模式台风涡旋以改进台风预报的方法。使用QuikSCAT海面风资料，针对中纬度和热带地区使用不同的边界层模式反演出与观测风场动力相适应的海平面气压；然后基于三维变分动力约束将海平面气压同化进入中尺度模式。对登陆中国的两个台风个例的初始化敏感性数值试验研究发现，初始化方法在实现台风风场与气压场的动力平衡的基础上，不仅通过调整边界层入流结构和垂直风切变明显改变了大气不稳定状态和对流触发条件，而且，也调整了台风在对流层顶附近的流出结构。尤其值得注意的是，尽管同化只是使初始台风强度略有加强，但随着模式积分时间的增长，这种模式边界层物理过程与资料同化相互耦合的方法对台风预报的影响在逐渐加强，改善了对台风登陆过程中强度维持和迅速减弱阶段的描述；并通过不同程度地调整对流层中低层和高层引导气流，改善了台风路径的数值模拟。

英文摘要:

      On the basis of the dynamic retrieval of sea level pressure and data assimilation， a new approach to vortex initialization is proposed and examined in this study for typhoon prediction. Two of the boundary layer numerical models designed respectively for mid latitude and tropical regions are introduced to retrieve the sea level pressure （SLP） in dynamic consistency with the QuikSCAT sea winds. The SLP retrieval is then assimilated into a meso-scale numerical model in two steps with the three-dimensional variational (3DVAR) data assimilation technique. Sensitivity experiments for two typhoons made landfall on the east coast of China show that the status of boundary layer stability can be influenced by the assimilation, which is associated with the vertical wind shear within the boundary layer inflow. The vortex initialization also affected the outflow structure of vortex near the tropopause. Most importantly, the coupling between the boundary layer physics and the data assimilation favored the simulation of typhoon intensity, in which the positive effects of assimilation become more evident with the increase of model hours. The maintenance and rapid weakening phases of intensity are more reasonably reproduced in the sensitivity experiments than that in the control run. Finally, the new technique enhanced the simulation of the typhoon track through the adjustment of steering flow on the various pressure levels. 