Abstract
A squall line that occurred in south China on 31 March 2014 was simulated with the Weather Research and Forecasting model. The microphysical processes had an important influence on the dynamic and thermodynamic structure of the squall line. The process of water vapor condensation (PCC+) provided heat for the ascending movement inside the squall line. The forward movement of the heating area of PCC+ was an important reason for the squall line’s tilting. The convergence of the outflow of the cold pool and the warm and wet air constantly triggered new convection cells in the front of the cold pool, which made the squall line propagate forwards. The cooling process of graupel melting into rain corresponded closely with the rear inflow jet. During the mature period of the squall line, the effect of cooling strengthened the rear inflow jet. This promoted low-layer inflow and a convective ascending motion, thus further promoting the development of the squall line system. During the decay period, the strong backflow center of the stratospheric region cut off the forward inflow of the middle and low layer towards the high layer, and cooperated with the cold pool to cut off the warm and wet air transport of the low layer, making the system decline gradually.
Highlights
Squall lines are mesoscale convective systems typically characterized by their sudden emergence, fast speed of movement, and rapid evolution
Since the squall line occurred in an area of strong wind shear, which itself was caused by the superp osition of a strong jet and relatively cold air at the top and warm and wet air at the bottom, we produced a regional-mean Skew-T diagram to analyze the atmospheric stratification during the squall line process (Figure 3)
The Dynamic and Thermodynamic Structure and Microphysical Characteristics of the Squall Line. Since this squall line case in South China occurred in the background of the humidity of the East Asian Monsoon and a strong development of the northeast cold vortex, the characteristics of its dynamic, thermodynamic and microphysical structure are unique with respect to their spatial and temporal distribution
Summary
Squall lines are mesoscale convective systems typically characterized by their sudden emergence, fast speed of movement, and rapid evolution. Biggerstaff et al (1991) [12] and Braun et al (1994, 1997) [13,14] suggested that melting and evaporative cooling of precipitation particles have an important influence on the formation and organizational structure of squall lines These processes can trigger and maintain the downdraft of mesoscale convective systems [15,16]. Guo et al (2003) [17] proposed that the drag and melting of ice-phase particles and the evaporation of raindrops produce a negative buoyancy effect, which can generate a strong downburst When this strong downdraft becomes divergent near the ground, it instantly causes local severe winds. The observed radar reflectivity whose resolution is 1km is got from National Meteorological Information Center
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