Based on thunderstorm gales data in recent 40 years and the conventional and new monitoring data in recent 18 years in Shanxi Province, the spatial and temporal distribution of thunderstorm gales in Shanxi Province are analyzed firstly, and then the weather types, characteristic physical quantity thresholds and conceptual models of thunderstorm gales are studied by using the methods of cluster analysis and mesoscale weather analysis. The results show that the average number of thunderstorm gale days in Shanxi had the regional distribution characteristics with more in the north and less in the south, more in mountainous areas and less in plain, and more in western mountainous areas and less in eastern mountainous areas. The extreme thunderstorm gales mainly occurred in the north of Shanxi and Lüliang mountainous regions. The annual thunderstorm gales days in the western mountainous area showed an increasing trend, while there were no changes or decreasing trends in other areas. The thunderstorm gales mainly occurred from May to August, accounting for 75% of the total days of thunderstorm gales in the whole year, and thunderstorm gales occurred most frequently at 16:00 and 21:00 (Beijing Time) in a day. The flow patterns of thunderstorm gales in Shanxi are mainly divided into six types, which are forward-tilting trough, backward-tilting trough, transverse trough, subtropical high and low-level warm shear line, subtropical high and low-level cold shear line, and northwest air flow. The K index threshold of all patterns from April to May was significantly lower than that from June to September, while the temperature difference between 850 hPa and 500 hPa was obviously higher than that from June to September. When each pattern meets the characteristic physical quantity thresholds of each month, it can trigger the strong thunderstorm gale weather in Shanxi, while the flow pattern configuration of forward-tilting trough has the highest percentage of triggering extreme thunderstorm gales. Over the same period, the K indices of the patterns of backward-tilting trough, subtropical high and low-level warm shear line, subtropical high and low-level cold shear line are significantly higher than those of the patterns of forward-tilting trough and northwest air flow, while the Si index of the forward-tilting trough is obviously higher than that of other patterns, which indicated that the dynamic instability condition of the forward-tilting trough triggering thunderstorm gale is better than the thermal instability condition. The CAPE and 0 ℃ layer height thresholds of the patterns of subtropical high and low-level warm and cold shear lines are significantly higher and the thresholds of T-T_d and cloud top black body temperature in the lower layer are significantly lower than those of the other four patterns. Whether hail is accompanied by thunderstorm gale process can be accurately judged by 0 ℃ layer height threshold of each month.

Based on daily precipitation data from 1960 to 2019 and hourly precipitation data in September 2019 from 109 meteorological stations in Shanxi Province and reanalysis data from European Centre of Medium-Range Weather Forecasts, the anomaly characteristics of the extremely regional rainstorm in central and southern Shanxi from 10 to 11 September 2019 and its causes were analyzed. The results are as follows: (1) The precipitation process affected a large area and lasted a long time, extreme daily precipitation events occurred at 46 stations, the daily precipitation of 11 stations exceeded the historical extreme value in September. (2) The water vapor, thermal and dynamic conditions in the middle and lower troposphere were better than the average state of regional rainstorm processes in the middle and south region of Shanxi since 1980, absolute values of normalized anomaly (|N|) of different physical quantities were higher than 2.5 and the upper quartile of historical data, especially for the water vapor and thermal conditions anomaly. (3) The subtropical high was anomalously strong and moved northward and westward, which led to abnormally strong water vapor and energy transport in mid-low troposphere, water vapor input in the western and southern boundaries of central and southern Shanxi Province played an important role in occurrence and development of extreme precipitation. (4) There was the potential instability in the inclined warm-moist southwesterly, warm shear line on 700 hPa and surface cold front initiated the convection, “train effect” produced due to echo moving continuously through heavy rain area. The stabilized shear line and abnormally cold wedge in lower troposphere provided sustained dynamic condition, abnormally plentiful vapor and its convergence maintained sustainably, which was the main causes of the extreme regional rainstorm, and the large range of physical quantities anomaly was the main influence factor of it.

Based on the infrared and water vapor cloud images of Himawari-8 satellite, the visible cloud images of FY-2E satellite, the composite reflectivity factor mosaic maps of Doppler radar, the observation data of conventional weather stations and automatic weather stations and radionsonde data, the cloud image characteristics and maintaining mechanism of the squall line process in Shanxi Province on 21 September 2017 were analyzed. The results are as follows: (1) The squall line weather process was caused by the large-scale Mongolia cold vortex weather system. The surface cold front moved eastward to the unstable potential area, which triggered the formation of the squall line system. The transformation of system configuration structure in high and low level of troposphere and the formation of mesoscale cyclone and convergence line from the outflow cold air of surface mesoscale high pressure and environmental wind field were the development and maintenance mechanisms of the squall line. The convective cloud clusters merged and developed between the surface cold front and 850 hPa shear line, and the development of surface mesoscale high and low pressure increased the pressure gradient, which led to the enhancement of the squall line, and further caused surface gale during the passage of the squall line. (2) At the initial stage, the squall line was formed in the large gradient area behind the low cloud-top brightness temperature region, the rough texture area of cloud-top, the wet side of the dry and wet boundary, and the position of cold cloud cover slightly moved in front of the squall line. At the development stage, the echo of the squall line strengthened in low cloud-top brightness temperature region, and it moved along the moving direction of the low value center of brightness temperature. At the mature stage, the radar echo of the squall line coincided with the low value region of cloud-top brightness temperature. (3) The arcus cloud line, the up rushing cloud-top and the shadows on one side of convective cloud belt were the early signs of the development and enhancement of convective cloud clusters.