Unraveling the Genesis of the 7.20 Zhengzhou Rainstorm: An Analysis with a Focus on Severe Convective Rain Cell Evolution
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摘要: 2021年7月20日，河南省在异常偏北的西太平洋副热带高压、发展加强的台风“烟花”以及西南季风的共同影响下产生了暴雨，造成了严重的生命财产损失，其中郑州市受灾最为严重。基于Himawari-8卫星云顶亮温数据，利用迭代对流云团追踪算法，对此次暴雨过程的强对流云团进行识别与追踪，探究暴雨发生的原因。结果表明，造成此次暴雨过程的强对流云团于7月20日10∶10在河南省北部生成，受太行山和嵩山的阻挡以及台风西侧东南水汽持续输送在移动过程中不断发展加强，生命周期长达9.3 h。郑州暴雨开始于对流云团最强盛时刻，而暴雨维持期间，强对流云团面积逐渐减小、云顶亮温持续升高，不稳定能量的释放和降水的拖曳作用促进了云团的减弱，云团迅速消亡，降水停止。上述研究表明在水汽持续输送和地形阻挡影响下，强对流云团发展加强和长时间盘踞是造成郑州特大暴雨的直接原因。Abstract: Under the joint influence of the relatively stronger and more northerly western Pacific subtropical high, intensified Typhoon In-Fa and the southwest monsoon, a heavy rainstorm struck Henan Province, China, on July 20, 2021. The rainstorm event caused severe casualties and economic losses in many cities, with Zhengzhou being the worst-hit region. Based on the cloud-top brightness temperature data of the Himawari-8 satellite, this study used the iterative convective rain cell tracking algorithm to identify and track the main convective rain cells of the rainstorm event and explored the causes of the rainstorm. The results show that the severe convective rain cells formed at 10:10 on July 20 in northern Henan Province and maintained for 9.3 hours, continuously strengthened by the blocking effect of Taihang Mountains and Songshan Mountain and supplied by the water vapor in southeasterlies. The rainstorm began at the strongest stage of the convective rain cells. During the rainstorm, the size of the severe convective rain cells gradually decreased, and the cloud-top brightness temperature kept rising. The precipitation gradually weakened because the released instability energy and the dragging flow caused the rain cells to weaken. The research shows that the development and long-stay of severe convective Rain Cell, driven by continuous water vapor transport and topographic blocking, was the direct cause of the heavy rainstorm that struck Zhengzhou on July 20, 2021.
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图 1 2021年7月20日(北京时间，下同)河南地区降水强度分布(a、b，填色，单位: mm·h-1)及云顶亮温分布(c、d，填色，单位: K)
黑色实线表示河南省省界及市界。
图 2 第一模态左场(a)、第一模态左场时间序列(b)、第一模态右场(c)、第一模态右场时间序列(d)
降水为SVD左场，云顶亮温为SVD右场。b、d中横坐标为2021年7月20日00时—21日00时。
图 3 2021年7月19—20日河南地区云顶亮温分布(填色，单位: K)
红色边框表示IRT算法识别的云团边界，数字表示云团编号，黑色实线表示河南省省界及市界，*标注郑州位置。
图 4 2021年7月19日08时(a)和20日14时(c) 500 hPa高度场(黑色等高线，单位: gpm)、风场(矢量箭头)和925 hPa水汽通量散度(填色，单位: g·cm-2·hPa-1·s-1)，2021年7月19日08时(b)和20日14时(d) 850 hPa的比湿(填色，单位：g·kg-1)和风场(矢量箭头)
蓝色实线表示河南省省界。
图 6 2021年7月20日河南区域云团识别图(a)和云团轨迹(b)
a中填色为云顶亮温(右侧色标，单位: K)和高程(下侧色标，单位: m)，红色边框表示IRT算法识别的云团边界，数字表示云团编号。b为a中编号1的云团轨迹，圆形表示不同时刻的对流云团，填色表示云团的平均云顶亮温(单位: K)，数字标记云团的追踪时次，起始时刻为2021年7月20日10:10，时间步长为10 min。
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