全球数值模式中的台风初始化Ⅱ: 业务应用

The initialization of t ropical cyclones in the NMC global model Part Ⅱ: Implementation.

  • 摘要: 中国国家气象中心基于全球数值模式、采用人造bogus涡旋初始化方案建立起来 的台风数值预报业务系统是独立于全球资料分析同化—预报循环过程来运行的。实际上,台风涡旋是全球数值预报中一个重要的、密不可分的中尺度系统,台风的正确描述会对周围的 大尺度形势预报产生积极正面的影响,而这种影响反过来也会反馈到大尺度环流对台风移向移速的变化上,陈旧的台风初始化方案和不合理的台风数值预报业务系统流程已经严重阻碍了中国台风数值预报业务水平的进一步发展。最近,中国国家气象中心利用新开发的台风初始化方案、基于全球数值模式建立了新一代的台风数值预报业务系统,相比于旧系统而言,新系统巧妙地将台风初始化过程与全球资料分析同化—预报循环系统融合在了一起,这使得改进目前台风路径数值预报效果成为可能。应用新的台风数值预报系统,文中对2006年生成于西北太平洋23个不同类型的台风进行了连续数值试验,统计分析表明,新系统在改进台风路径 预报效果上有了不俗的表现,相比于业务使用的人造bogus涡旋方案而言,120 h预报时效 内的平均路径误差有了十几公里到上百公里的下降。该系统在2007年台风季节投入了实时试验运行,并取得了令人惊喜的预报效果。

     

    Abstract: Currently, the TC numerical prediction system at National Meteorological Center (NMC) of China is based on a global model using the initialization scheme of in serting a bogus vortex into the analysis field. Because the structure of the bog us vortex is not dynamically and physically consistent with the global model, the TC prediction system has always been run independent of the global analysis forecast cycle since it was put into operation. In fact, TC circulation is one of the important components of largescale analysis. An accurate description of initial TC structure will produce a positive effect on forecasting of large-scale circulation. In return, the large-scale circulation can steer TC's moveme nt and speed correctly at each forecast time. Obviously, the TC prediction syste m with the bogus vortex scheme is so antiquated that it cannot provide better fo recasts of TC track for operational use. Recently, a new TC numerical prediction system has been developed using a new TC initialization scheme based on the glo bal analysisforecast cycle in order to increase the skill of TC track forecasts. While the bogus vortex initialization of the old operational prediction syste m is carried out after data analysis, the TC initialization of the new system is accomplished before data analysis. It is significant that a few observations related to TC are not rejected during the quality check of the data assimilat ion, because the background field in which TC has been initialized is more consi stent with observational data. The new TC numerical prediction system for TC for ecasts over the western North Pacific was established at NMC in late 2006. To e valuate the impact of the new scheme on TC track predictions, 23 different TCs d uring the 2006 TC season were examined, which enables us to identify the case to case variability in the forecast results. It was found that the new scheme produced more accurate TC track forecass compared with the old bogus scheme. Statistical analysis shows a decrease in the average track error by 11%-23% in th e 12 to 120 h forecast time periods for the 2006 typhoon season. The new TC nume rical prediction system was applied to operational forecast parallel tests in th e 2007 typhoon season and it showed improved performance in TC track forecasts. The system was scheduled to be into operation in place of the old TC system in 2008.

     

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