“21·7”河南暴雨环境场及云的宏微观特征

Environmental Conditions and Cloud Macro and Micro Features of "21·7" Extreme Heavy Rainfall in Henan Province

  • 摘要: 利用FY-4A静止气象卫星、FY-3D极轨气象卫星资料和ERA5再分析资料,深入分析“21·7”河南暴雨环境场及云宏微观特征,首次利用FY-4A观测研究此次事件对流云微物理特征。结果表明:“21·7”河南暴雨是一次极端强降水事件,河南省位于大陆高压和副热带高压之间的鞍型场内,有利于其上空低涡云系的发展和维持。2021年7月20日两股水汽输送交汇于河南中北部,为郑州极端降水提供了有利条件。20日14:00—16:00(北京时,下同)郑州长时间位于对流云团冷云区边界亮温梯度大值区,该时段对流发展旺盛;12:00—14:00云光学厚度跃增,且在15:00仍维持较大值,表明该时段云中液态粒子大量合并,液态水含量丰富,光学厚度峰值出现时间先于降水量峰值出现时间,FY-4A云光学厚度跃增且维持较大值对强降水出现时间及量级有重要的预警意义。对流云粒子有效半径(re)随温度(T)的增长曲线(T-re关系)表明:20日16:00河南上空的雨胚形成区最为深厚,云中不同高度的re整体维持在20~25 μm,表明云中上升气流较强,有利于地面强降水发生。

     

    Abstract: Meteorological satellites can provide more details of cloud, which can be used to analyze the development process of convective cloud in the rainstorm events. To investigate the "21·7" extreme heavy rainfall in Henan Province, satellite cloud image characteristics, the development and evolution process of precipitation clouds, macro structure and microphysical features are deeply analyzed by FY-4A satellite data, FY-3D satellite data, and ERA5 reanalysis data. Particularly, FY-4A satellite data are used to study the cloud microphysical features of this event for the first time. The boundary position and intensity of the water vapor dark area of continental high are relatively stable from 18 July to 22 July in 2021, and the subtropical high continues to extend westward. The stable saddle field is conductive to the long-term development and maintenance of the low vortex cloud system over Henan Province. Two streams of water vapor locate at the north central part of Henan Province, which is favorable for the occurrence of rainstorm at Zhengzhou on 20 July. The reorganization and adjustment of the convective system are due to the consolidation and development of several convective clouds over Henan Province on 20 July. From 1400 BT to 1600 BT, the boundary of cold cloud is over Zhengzhou, where the brightness temperature gradient value is large, indicating that the convection is in its development stage. Furthermore, the cloud optical thickness increases from 1200 BT to 1400 BT, and still maintains a large value at 1500 BT. It indicates that this period is critical for a large number of liquid particles to merge. The time when the cloud optical thickness reaches peak value is prior to that of the precipitation. The increasing trend and value of cloud optical thickness have great significance for the magnitude and occurrence time of heavy rainfall. The relations between cloud top temperature and particle effective radius(T-re relations) are analyzed by FY-4A data. The results show that the rain zone over Henan Province is the deepest at 1600 BT 20 July, and the effective radius of cloud particles at different heights maintain at 20-25 μm. It indicates that the updraft in the cloud is strong, which is conductive to the occurrence of heavy rainfall.

     

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