基于条件非线性最优扰动的目标观测中瞄准区不同引导性变量的影响试验研究

Experimental studies of the impacts of the different guidances of targeting areas on the targeting observations based on the CNOP method

基于GRAPES区域业务预报模式,采用一种快速算法计算出来的条件非线性最优扰动对实际台风个例麦莎(No.0509)开展了目标观测研究,应用数值模式,进行一系列的敏感性试验,讨论了与目标观测设计相关的一些问题,包括确定瞄准区时使用不同的引导性变量对目标观测效果的影响、及瞄准区范围变化对预报效果的影响。文中分别以提高麦莎在检验区(20.125°—35.3125°N,116.8125°—129.75°E)内的24 h海平面气压预报和24 h累积降水量预报为目的,基于条件非线性最优扰动使用了3种不同的引导性变量寻找敏感区(又称瞄准区),对这些敏感区的分布特点和有效性进行了比较和讨论。试验结果表明,在使用的3种引导性变量中,用不同的引导性变量识别的敏感区是有差别的,总体上说,文中使用的3种引导性变量识别的瞄准区对提高预报都是有效的,特别是第2和第3种的效果更好些,且两者识别的瞄准区常显示出类似的特点。文中进一步针对检验区内24 h累积降水量预报误差问题,将前面确定的瞄准区范围扩大相同的幅度,讨论瞄准区范围变化对改进预报的影响。试验结果表明,增加瞄准格点数,有可能使预报效果得到改善,但是试验结果同时也暗示了单纯靠扩大瞄准区的范围未必一定能减小预报误差,这与不同的引导性变量对瞄准区范围大小的敏感性不同有关。

The conditional nonlinear optimal perturbations （CNOPs） obtained by a fast algorithm are applied to the targeting observations of Typhoon Matsa （2（}05） based on the Global/Regional Assimilation and PrEdiction System （GRAPES）, an op- erational regional prediction model. Through a series of sensitivity experiments, several issues on targeting strategy design are discussed, including the effectivity of different guidance to determine the sensitive area （or targeting area） and the impact of the size of targeting area on the improvement of 24-hour forecast. Three guidances are used when employing the CNOP for finding the targeting area to improve the 24-hour sea lever pressure prediction and 24-hour accumulated rainfall prediction in the verifi- cation region （i. e. 116. 8125^--129.75~E, 20. 125^--35. 3125~N）. The distribution and effectivity of these targeting areas are compared with each other with the results that the sensitive areas identified by the three guidances used in this study are differ- ent from each other. All the sensitive areas determined by these guidances are effective in that the improvement of the 24-hour forecast is reached. The last two guidances are more effective and able to identify more similar sensitive areas than the first one. Further, when the size of targeting areas is enlarged twice it is noticed that the 24-hour accumulated rainfall prediction is not necessarily improved since although an initial condition improvement in a larger size of targeting area may sometimes result in a better prediction skill, it is not always true, depending on the sensitivity of the guidance to the size of targeting area.