Abstract:Based on conventional meteorological data, ECMWF ERA-Interim 0.125°×0.125° analysis data,FY-2G satellite images and doppler radar data, the mesoscale characteristics and precipitation causes in the extremely rainfall process occurred in Luohe on 18-19 August was analyzed. Results show that: (1) The process occurred in the favorable configuration of 200 hPa jet diversion area, 500 hPa trough and the subtropical high, jet shear in the middle and lower layers and surface low-pressure trough. (2)The sounding showed that there was a high convective potential over Luohe, which helped the convective rain clusters newborn and development. Saturated humidity, thick warm cloud heights and weak wind shear were beneficial to storm clouds. High CAPE values, high specific humidity and high precipitation efficiency all were important reasons for the extremely rain clusters. (3) While the convective cloud moved eastward with the southwest airflow in front of the trough, the other one in the lower shear line moved southward, opposite merging into MβCS, which was different from the previous merging cloud clusters in the region and was conducive to the enhancement of storm clouds. The continuous train effect and backward propagation of low-mass and high-efficiency mesoscale convective monomers lead to long-term maintenance of strong echo and the development of extreme precipitation. (4) The surface convergence line with the strong convergence center acted the triggering force, which superimposed on the weather-scale shear line, lead to the maintenance of mesoscale rain clusters. The cold pool outflow interacts with the southeast and the eastward wind on the north of the junction, making the horizontal temperature gradient to increase to form front of the cold pool front. On one hand, it helped organizational development of mesoscale rain clusters and backward propagation of convective monomers. On the other hand, the new convection was triggered downstream of the precipitation area and the cold pool continued to increase. (5)The wind field in the whole layer was weak and the low-level airflow propagation speed was more than the guiding airflow. The reverse angle was large between them, resulting in the large deviation from the direction of the guiding airflow. At the same time, the deceleration effect caused the mesoscale system moving slowly, which was conducive to extreme precipitation.