一种基于分析增量更新技术的台风初始化方案

A typhoon initialization scheme based on incremental analysis updates technology

  • 摘要: 台风初始化方案最大的困难在于其只能根据有限的观测资料(台风中心位置、最低气压、最大风速和大风半径等)来构造一个与模式动力-物理过程协调的涡旋模型。首先根据实际观测资料对背景场中的涡旋扰动进行重定位和风速调整,然后将分析增量更新(Incremental Analysis Update,IAU)技术应用于台风初始化方案中,将调整后的涡旋当作一个强迫项逐渐加入到模式预报过程中,通过模式自身调整来得到一个协调性较好的台风初始结构,从而改善模式对台风的预报性能。对“山竹”台风的多次预报结果表明:(1)台风初始化对于台风路径误差影响较小,对于强度预报改进则比较明显。特别是在台风生成初期,台风初始化技术能够有效地增强全球模式分析场中的涡旋强度,并解决预报过程中强度较弱的问题。(2)根据预先给定的三维风场,IAU技术能通过模式自身预报过程对其他变量进行调整,从而得到一个热力和动力协调的初始涡旋结构。相对于仅对初始风场的调整,它对24 h之后的路径和强度预报误差会有更进一步的改善。(3)对IAU中的松弛时间进行参数敏感性试验,发现该变量取3—6 h效果较好。

     

    Abstract: The main difficulty in typhoon initialization lies in how to generate variables that are consistent with the prescribed wind field based on limited observational data (such as the location of typhoon center,the minimum pressure,the maximum wind speed,and the size of typhoon). In this study,the IAU (Incremental Analysis Updates) is introduced into typhoon initialization scheme to solve this problem. The background vortex perturbation is relocated and adjusted first according to observations,other variables are then generated by the model through a strong 6 h nudging to the prescribed wind field. Multiple forecast experiments for typhoon Mangkhut indicate that:(1) The influence of typhoon initialization proposed in the present study on the track forecast is weak,while the forecast of intensity is significantly improved. Especially in the generation stage,the intensity of the typhoon is strengthened after initialization process and becomes more consistent with observation. (2) The IAU technology can make adjustment on other variables according to the prescribed wind field,and produce a more thermally and dynamically consistent vortex structure. The forecast of typhoon track and intensity is further improved after the IAU technology is implemented. (3) Sensitive experiments indicate that the relaxing time of 3-6 h can yield the best result.

     

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