关键词: 下击暴流, 精细化资料, 低空风切变, 热力不稳定, 动量下传

Abstract:

The cause of a continuous downburst weather occurring in southwestern Anhui Province on 2 May 2016 was analyzed based on Doppler radar data, lightning positioning data, ground observation data and field investigation. The results showed that the storms causing two micro downbursts were actually the same supercell. The radar echoes during the strong stage showed a hooking distribution and declining structure. The downburst was resulted from the dragging force of liquid or solid particles at the initial stage, and derived from the thermal instability, momentum downward in middle level of troposphere and compensatory airflow at the middle and late stage. The negative buoyancy between the water matter and environment increased, which was an important factor causing the downburst, and the direction of prevailing wind in middle level of troposphere causing momentum downward decided the trend direction of ground wind of micro downburst. It’s worth noting that the supercell had not only the highest reflectivity factor nuclei with 6 km above, but also the fastest falling speed with 3 km around or above within a volume-scanning time interval (6 minutes). At the same time, the 6-minute accumulative precipitation reached 4 mm and above, which heralded the possible occurrence of downburst.

Key words: downburst, refined data, low-level wind shear, thermal instability, momentum downward