Predictability of the 7·20 extreme rainstorm in Zhengzhou in stochastic kinetic-energy backscatter ensembles

IF 6 2区 地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY
Min Yang, Peilong Yu, Lifeng Zhang, Xiaobing Pan, Quanjia Zhong, Yunying Li
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Abstract

The scale-dependent predictability of the devastating 7·20 extreme rainstorm in Zhengzhou, China in 2021 was investigated via ensemble experiments, which were perturbed on different scales using the stochastic kinetic-energy backscatter (SKEB) scheme in the WRF model, with the innermost domain having a 3-km grid spacing. The daily rainfall (RAIN24h) and the cloudburst during 1600–1700 LST (RAIN1h) were considered. Results demonstrated that with larger perturbation scales, the ensemble spread for the rainfall maximum widens and rainfall forecasts become closer to the observations. In ensembles with mesoscale or convective-scale perturbations, RAIN1h loses predictability at scales smaller than 20 km and RAIN24h is predictable for all scales. Whereas in ensembles with synoptic-scale perturbations, the largest scale of predictability loss extends to 60 km for both RAIN1h and RAIN24h. Moreover, the average positional error in forecasting the heaviest rainfall for RAIN24h (RAIN1h) was 400 km (50–60) km. The southerly low-level jet near Zhengzhou was assumed to be directly responsible for the forecast uncertainty of RAIN1h. The rapid intensification in low-level cyclonic vorticity, mid-level divergence, and upward motion concomitant with the jet dynamically facilitated the cloudburst. Further analysis of the divergent, rotational and vertical kinetic spectra and the corresponding error spectra showed that the error kinetic energy at smaller scales grows faster than that at larger scales and saturates more quickly in all experiments. Larger-scale perturbations not only boost larger-scale error growth but are also conducive to error growth at all scales through a downscale cascade, which indicates that improving the accuracy of larger-scale flow forecast may discernibly contributes to the forecast of cloudburst intensity and position.

随机动能反向散射集合中郑州 7-20 特大暴雨的可预测性
通过集合试验研究了 2021 年中国郑州破坏性 7-20 特大暴雨的尺度可预报性,试验采用 WRF 模式中的随机动能反向散射(SKEB)方案对不同尺度进行扰动,最内层域的网格间距为 3 公里。考虑了日降雨量(RAIN24h)和 1600-1700 LST 期间的云爆(RAIN1h)。结果表明,随着扰动尺度的增大,降雨量最大值的集合差值也随之增大,降雨量预报也更接近于观测值。在具有中尺度或对流尺度扰动的集合中,RAIN1h 在小于 20 千米的尺度上失去了可预测性,而 RAIN24h 在所有尺度上都具有可预测性。而在有切变尺度扰动的集合中,RAIN1h 和 RAIN24h 可预测性损失的最大尺度都达到了 60 千米。此外,RAIN24h(RAIN1h)预报最强降雨的平均位置误差为 400 千米(50-60)千米。郑州附近的偏南低空喷流被认为是 RAIN1h 预报不确定性的直接原因。低层气旋涡度的快速增强、中层辐散以及与喷流同时出现的上升运动在动力学上促进了云爆。对发散、旋转和垂直动能谱以及相应误差谱的进一步分析表明,在所有实验中,较小尺度的误差动能比较大尺度的误差动能增长更快,饱和也更快。较大尺度的扰动不仅促进了较大尺度误差的增长,而且还通过下尺度级联效应促进了所有尺度误差的增长,这表明提高较大尺度气流预报的精度可能明显有助于云爆强度和位置的预报。
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来源期刊
Science China Earth Sciences
Science China Earth Sciences GEOSCIENCES, MULTIDISCIPLINARY-
CiteScore
9.60
自引率
5.30%
发文量
135
审稿时长
3-8 weeks
期刊介绍: Science China Earth Sciences, an academic journal cosponsored by the Chinese Academy of Sciences and the National Natural Science Foundation of China, and published by Science China Press, is committed to publishing high-quality, original results in both basic and applied research.
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