瞬时扰动法在佛山一次台风龙卷的环境背景分析和模式预报中的应用

The Applying of Temporal Climatology Method in the Analysis of both Environmental Background and Model Forecasting for a Typhonic Tornado in Foshan

  • 摘要: 结合欧洲中期天气预报中心(ECMWF)ERA5再分析数据与S2D模式输出产品,利用瞬时扰动法先提取了2018年9月17日台风“山竹”在佛山地区诱发的台前龙卷前期“扰动天气系统”,接着评估了业务模式对此过程前期扰动天气系统的预报能力。结果表明:龙卷易发生于负高度扰动轴线和冷暖气团对比零线的重合之处;龙卷是在台风登陆之后高空扰动暖气团和近地面负高度扰动明显减弱阶段发生的,此时近地面有扰动冷气团开始发展;佛山在龙卷发生前1 h转受近地面的较强的东南风和偏南风扰动辐合影响,而中高层大气受冷平流扰动影响,大气层结变得不稳定;负高度扰动和正湿涡度扰动有利于台风龙卷母体风暴发生发展,但会抑制下沉气流扰动的出现,而正湿散度扰动增大引起的下沉气流扰动增强;业务模式起报时间为最新时次的预报结果对全部扰动场的综合预报能力是最好的,预报提前量有12 h。

     

    Abstract: Basing on the ERA5 reanalysis data and S2D model output of European Centre for Medium-Range Weather (ECMWF), this paper extracts the tornado-related anomalous systems, occurring in Foshan in September 17, 2018 induced by the typhoon ‘mangkhut’, by using temporal climatology method and evaluates the operational forecasting model. The conclusions are listed below. Firstly, this tornado was more likely located at the overlap between axis of negative anomalous height and zero line of anomalous temperature. Secondly, this tornado occurred during the decay stage of both the positive anomalous temperature in the higher and negative anomalous height in the lower, accompanying with a development of negative anomalous temperature.Thirdly, The inf luence of prevailing wind in Foshan, before this tornado arised, shifted to the convergence between the anomalous southeaster and southerly wind near the ground and the mid-level atmosphere above was affected by negative anomalous advection, resulting in a unstable atmospheric stratif ication. Fourthly, negative anomalous height and positive anomalous moist vorticity were in favor of strengthening of tornadic parent storm and suppressing the downdraft, while positive anomalous moist divergence can enhance the downdraft. Lastly, the capacity of forecast of operational forecasting model, for all fields generally, is the best when the initial forecast time is latest, which can predict this tornado in advance of 12 hours.

     

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