双台风“玛娃(2005)”和“古超(2005)”移动路径与强度的伴随敏感性分析

The adoint-derived sensitivity analysis of the motion and intensity of the binary typhoons:Mawar(2005) and Guchol(2005)

本文利用WRF模式及其伴随模式研究了2005年发生在西北太平洋的一对双台风玛娃和古超的移动路径与强度的伴随敏感性特征,一方面探讨了环境场对双台风的影响,另一方面也讨论了双台风之间的相互影响过程的差异.首先,利用双台风初始化技术准确地模拟了双台风的演变过程,并以此模拟结果为背景场计算了台风的中心扰动气压和引导气流的伴随敏感性.研究结果表明:伴随敏感性不但能反映环境场对双台风的影响,还能指示双台风之间相互影响过程的差异.从台风强度的敏感性来看,影响台风强度变化的高影响区均位于台风中心附近,弱台风古超的强度敏感性的量级要大于强台风玛娃的强度敏感性,表明双台风中较弱的那个更容易受到外部环境变化的影响.台风引导气流的敏感性分布也存在较大差异,强台风玛娃的移动主要受到其西北侧的高空槽,其自身环流以及台风古超的影响,而弱台风古超的引导气流的敏感性主要位于其自身环流附近以及双台风之间的区域.最后,通过在理想试验中增加初始时刻高空槽的强度以及弱台风古超的强度,证实了台风玛娃的移动路径的变化与伴随敏感性的分析一致.

In this study,the weather research and forecasting(WRF)model and its adjoint model were employed to explore the binary interaction and environmental impact on a binary typhoon case:Mawar and Guchol occurred in the western North Pacific in 2005.First,a dynamical initialization scheme for binary vortices was used to improve the numerical simulation,and then this simulation was used as the background for the adjoint model calculcation.Two response functions,the typhoon central surface perturbation pressure and the steering vector,wereselected to represent the intensity and motion of typhoons,and the adjoint-derived sensitivity steering vector(ADSSV)was also calculated.The results showed the adjoint-derived sensitivity can indicate both the environmental impact on the two typhoons and the binary interaction between them.Large discrepancy existed between the amplitudes and spatial distribution of the intensity sensitivities of the two typhoons,the weaker typhoon had stronger sensitivities,indicating that the weaker typhoon was more sensitive to the initial perturbations.The distribution of ADSSV indicated that the motion of typhoon Mawar was the results of comprehensive action by the trough in the west,typhoon Guchol and itself,whereas,the ADSSV of typhoon Guchol mainly located at the vicinity of its central circulation.At last,through changing the initial intensity of the typhoon Guchol and the upper trough,the variations typhoon Mawar′s motion were consistent with the indications by the adjoint sensitivity analysis.