Subseasonal Predictability of the July 2021 Extreme Rainfall Event Over Henan China in S2S Operational Models
Subseasonal Predictability of the July 2021 Extreme Rainfall Event Over Henan China in S2S Operational Models
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DOI：
10.1029/2022jd037879
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发表时间：
2023-02
期刊：
影响因子：
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通讯作者：
Yuhan Yan;Congwen Zhu;Boqi Liu
中科院分区：
文献类型：
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作者：
Yuhan Yan;Congwen Zhu;Boqi Liu
2021年7月17日至23日，河南省郑州市发生了创纪录的洪涝灾害中国，造成数百人死亡和巨大的经济损失。在这里，我们评估了这次极端降雨事件的可预测性和热带气旋(TCS)的影响，使用亚季节到季节性(S2S)业务模式。在月尺度上，大多数在6月下旬启动的模式较好地预测了7月份中国降水异常的北湿南干格局，并伴随着西北太平洋副热带高压的西伸和南亚高压的东伸。在周时间尺度上，只有4个模式提前1周捕捉到了降水极值的位置、概率和突然加强，这主要是由于它们对中纬度WNPSH变率的合理预测。然而，S2S模型仍然低估了这一事件的超级极端。预报的偏差来自于台风IN-FA的可预报性较差，以及它对极端降雨事件的每日演变的影响，甚至在预报提前几天内也是如此。与观测结果相比，热带扰动的预报偏差改变了环境季风气流，导致IN-FA形成前的极端降水预警。IN-FA形成后，台风移动速度的预测偏差扭曲了台风的位置，错误地预测了水汽辐合中心，低估了它们对这次暴雨过程的远程影响。
A record‐breaking flooding event occurred in Zhengzhou, Henan Province of China during 17–23 July 2021, causing hundreds of deaths and vast economic losses. Here, we evaluated the predictability of this extreme rainfall event and the impacts of tropical cyclones (TCs) using subseasonal‐to‐seasonal (S2S) operational models. On the monthly timescale, most models initialized in late June reasonably predicted the wet‐in‐north and dry‐in‐south patterns of anomalous rainfall over China in July, accompanied by the well‐predicted westward extension of the western North Pacific subtropical high (WNPSH) and eastward stretching of the South Asian High. On the weekly timescale, only four models captured the location, probability, and sudden intensification of the rainfall extremes in advance of 1 week, largely due to their reasonable prediction of WNPSH variability in mid‐latitudes. However, the S2S models still underestimated the super extremeness of this event. The prediction discrepancies came from the poor predictability of Typhoon IN‐FA and its impact on the daily evolution of the extreme rainfall event, even within a few days forecast lead. Compared with the observation, the prediction bias of tropical disturbance changed the environmental monsoon airflow to induce the earlier warning of rainfall extremes prior to the formation of IN‐FA. After the formation of IN‐FA, the prediction bias of the typhoon's moving speed distorted the typhoon location, which incorrectly predicted the moisture convergence center and underestimated their remote impacts on this heavy rainfall event.