位涡趋势诊断方法在高分辨率模式资料中的应用

位涡趋势（Potential Vorticity Tendency，PVT）诊断方法已经在台风移动研究中得到较多的应用，但是多用于水平分辨率几千米的模式输出资料。发现用位涡趋势方法诊断台风移动时，模式资料输出时间间隔必须与模式空间分辨率匹配，这是因为位涡趋势方法需要同时用时间和空间差分方法计算位涡的趋势和分布。当模式水平分辨率高于1 km时，模式可以模拟小尺度系统，相应的模式输出时间间隔必须缩短，使得模式输出资料能够代表小尺度系统的变化趋势。由于小尺度系统导致的位涡变化不能直接影响台风移动，建议应用两种方法解决位涡趋势方法中的时、空匹配问题:（1）当空间分辨率增加时，相应缩短模式输出资料的间隔；（2）不改变模式输出时间间隔，对计算位涡的物理量进行空间平滑，滤去小尺度系统的影响。 

Application of PVT method for diagnosing typhoon motion with high-resolution data

The PVT(Potential Vorticity Tendency) method has already been widely used in diagnosing the mechanism of typhoon motion. The spatial resolution of the data used in those studies is usually several kilometers. In the present study, it is found that when using the PVT method to diagnose typhoon motion, the time interval of the data should match its spatial resolution owing to the limitation of the calculation. The PVT and potential vorticity distribution were calculated by using the time difference and spatial difference methods at the same time. When the spatial resolution of the model is increased to less than 1 km, some small-scale systems are simulated. Thus, the time interval of the data should be reduced to make sure it can represent the variability of these small-scale systems. As the potential vorticity caused by these small-scale systems can not directly influence the typhoon motion, two methods are recommended in this study to solve this problem. The first one is to reduce the time interval of the model output data as its spatial resolution increases. The second one is to keep the time interval unchanged and do spatial smoothing on the variables used in calculating potential voricity so as to filter out these small-scale systems.