Environmental Characteristics of Regional Rainstorms under Different Circulation Backgrounds in Longdong, Gansu Province

To improve the forecast service of regional rainstorms in Longdong, the circulation characteristics of regional rainstorms in the region from 2010 to 2020 are analyzed by using conventional meteorological observation data, NCEP/NCAR reanalysis data, and Fengyun-2 (FY-2) satellite data. In addition, synoptic types and their differences are also studied. The results show that the regional rainstorms in Longdong can be divided into five types: Subtropical high type (which can be further divided into subtropical high type Ⅰ and subtropical high type Ⅱ), east-high west-low type, eastward-moving low trough type, low vortex type and northwest airflow type. Among them, the subtropical high type occurs most frequently, while the northwest airflow type occurs least frequently. The circulation patterns of all types show the presence of lifting triggering systems such as shear lines in the middle and lower levels, low-level jet streams or significant southerly winds, and surface convergence lines or cold fronts. The water vapor conditions are the most favorable for the subtropical high type and the east-high west-low type, whereas they are relatively poor under the low vortex type and the northwest airflow type. The dynamic conditions are the strongest for the low vortex type, while the weakest for the subtropical high type. The subtropical high type exhibits the strongest convective instability, while the eastward-moving low trough type and the east-high west-low type show relatively weaker convective instability. The northwest airflow type features the strongest vertical temperature differential advection. Cloud clusters associated with the subtropical high type are generally well-developed, with low cloud-top temperatures and strong convective precipitation. In contrast, cloud systems under the east-high west-low type show large variations, with strong convective activity in midsummer. For the eastward-moving low trough type, the cloud-top black body temperature (TBB) is relatively high, and convection is comparatively weak. Cloud systems under the low vortex type are mostly vortex- or comma-shaped, with large variations in convective intensity. The northwest airflow type mostly occurs in cloud-sparse regions or stratiform cloud regions, occasionally accompanied by scattered convective cloud clusters, and its average minimum TBB is the highest among all types.