“非bogus初值”热带气旋数值预报及其性能

“NON-BOGUSSING" INITIALIZATION FOR TROPICAL CYCLONE NUMERICAL PREDICTION AND ITS FEATURES

从高分辨模式特点及精细预报的需要出发 ,尝试了用”非bogus初值”开展热带气旋精细数值预报的方案。即直接采用四维同化形成的热带气旋 (TC)初值 ,而不再加入“人造台风”(BOGUS)信息 ,以图避免人为理想结构带来的虚假信息 ,对热带气旋路径、强度、结构等有更为精细和准确的预报。用 2 0 0 1年所有影响华南的TC实例 ,对方案的可行性进行了分析。结果表明 ,本方案可以较好地预报TC的生成 ;路径预报准确率较高 ,对疑难路径及局地效应反映较为细致 ,路径预报误差随时效增大不显著 ;强度趋势预报指示意义强 ,准确率较高 ;尤其是能很好地反映TC的云、雨、风等的非对称结构、螺旋结构等特征的时空演化 ,对TC中尺度结构的刻画能力和预报可用性较强。显示了方案的优越性和发展潜力 ,也意味着”非bogus初值”方案应该作为未来TC数值预报发展的一个主要技术方向。分析表明目前条件下本方案还存在一些不足之处 ,主要表现在因初始信息的不足 ,当在TC过弱、初生或远离大陆等情况下 ,常会出现初始场中TC位置和强度与实况偏差过大 。

For the demand of fine prediction and based on the features of high resolution models, the “non bogussing' initialization was tested to make fine prediction of tropical cyclones (TC), i.e., the initial fields from 4 dimensional assimilation was adopted, without adding the TC bogussing, to avoid illusive information induced from idealized TC structure, and to acquire finer or more accurate prediction to the track, intensity and structure of TCs. The feasibility of the scheme was evaluated by using all TC cases which affected the South China in 2001. The results show that the scheme has a better capability to predict the genesis of TCs, and higher accuracy for track prediction, with prediction errors unremarkably increasing with integral time, and especially reflects better the complicated track and local effects. While it shows a higher skill for TC intensity prediction in terms of intensity change. In addition, it reflects well the asymmetric and spiral structures of cloud, rainfall and winds for the TCs, showing well practicability. All of these revealed the advantages and developing potentials of the scheme, which implies that “non bogussing' initialization should be one of the main approaches for the TC numerical prediction techniques in the future. However, at the current condition, the scheme possesses some insufficiencies. The main problem is that due to the lack of observational information, larger errors may often occur in the initial TC position or intensity, which may cause larger prediction errors, when the TC is too weak, newly arising or far away from the mainland.