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

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-r_e 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.