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强对流天气概念模型在江西“3·4”极端大风预报中的应用

Application of severe convection weather conceptual model to forecast of an extreme gale event occurred in Jiangxi on 4 March 2018

  • 摘要: 对强对流天气12 h以上的潜势预报尤其是分类预报,目前仍是天气预报业务中的难点。2018年3月4日江西遭遇一次极端雷暴大风天气过程(简称"3·4"江西雷暴大风过程),虽然江西省气象台3月2日对外发布了区域性雷暴大风、冰雹等强对流天气预报,但对其极端性和开始影响江西的时间等事先估计不足。利用主流数值预报模式产品,对照强对流概念模型条件,对"3·4"江西雷暴大风过程的实时预报思路、经验和不足进行了总结分析与反思。结果表明:(1)该过程天气形势符合我国槽前暖平流强迫类强对流概念模型,其有利的环境条件为500 hPa有大经向度高空低槽东移,且槽前有干冷舌;低层有异常强盛的西南急流及脉动,其脉动加强特征与我国南方西南急流通常在早上加强的日变化特征完全不同;同时低层湿舌明显增强,与500 hPa形势对应,形成上干冷、下暖湿环境条件。(2)地面低压倒槽异常发展,超低空急流上有风向或风速辐合时,导致地面暖区辐合线生成,是判断强对流午后先在强西南气流的暖区中形成的重要判据之一。(3)3月4日江南地区850 hPa与500 hPa温差(T850-500)、对流有效位能(CAPE)等多个不稳定指数异常偏强,均明显高出其气候平均态。(4)深刻理解强对流概念模型、准确把握气象要素和物理量平均值态与异常、细致分析有别于其日变化的急流变化特征,是做好此类罕见致灾性雷暴大风潜势预报的关键着眼点。

     

    Abstract: The severe convective weather potential forecast, especially classification forecast of more than 12 hours in future is still one of the most difficult problems in forecasting operation at present. Jiangxi province encountered an extremely thunderstorm gale event (hereinafter referred to as the "3·4" gale event) on 4 March 2018. Although a forecast for severe convective weathers like regional thunderstorm gale and hail was issued by Jiangxi Meteorological Observatory on 2 March 2018, it was underestimated for the extreme intensity and beginning time of influencing Jiangxi. Based on numerical prediction models like ECMWF and comparing with the severe convective concept model, we have made a rethink for real-time forecast ideas, experiences and shortages of the "3·4" gale event. The results are as follows. (1) The synoptic situation of the "3·4" gale event meets the concept severe convective model of low-level prior-trough warm advection forcing type in China; it occurs under eastward movement of low trough with large degree of meridionality at 500 hPa and dry and cold tongue in front of trough. There exists an abnormally strong southwest jet pulsating in the low-level, whose strengthen is mostly different from that of southwest jet in south China in the morning in general. In addition, the significantly strengthening of wet tongue in the low-level is in coherence with the synoptic situation at 500 hPa, which causes the configuration of dry and cold air in the high and warm and humid air in the low level. (2) When the wind direction or velocity convergence occurs in the ultra-lower-level jet after surface low pressure with a warm inverted trough develops intensively, surface convergence line forms in the warm sector, which is an important criterion for severe convection weather occurred in warm sector of inverted trough. (3) Several instability indices, such as the temperature difference (T850-500) between 850 hPa and 500 hPa and CAPE, are significantly strong; they are higher than their climatological mean. (4) There are three key points to better forecast the extreme disaster-causing thunderstorm gale events, i.e. completely understanding the concept model of severe convection prediction, accurately grasping the averaged and abnormal values of the meteorological elements, and carefully analyzing the southwest jet pulse apart from its diurnal variation.

     

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