ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Archive > Volume 49 Issue 8 > 2023,49(8):932-945. DOI:10.7519/j.issn.1000-0526.2023.061201 Prev Next
Evolution Characteristics of Two Down-to-Hill Thunderstorms at the Northern Foot of Qinling Mountains
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Abstract:
On 26 July 2018 (shortly for “7·26”) and 29 July 2018 (shortly for “7·29”), the gust front formed by the cold outflow caused severe convective weather in the Guanzhong Plain, but their intensities, moving speeds and impact ranges were quite different. The difference characteristics and main reasons of the two down-to-hill thunderstorms are analyzed by using the ERA5 reanalysis data and multiple observation data. The results show that the “7·26” thunderstorm was highly organized, with a long lifespan and the maximum temperature change of 16℃·h-1 within the cold pool, thus resulting in a wide range of short-time severe rainfall and thunderstorm gale. By contrast, the “7·29” storm was dominated by isolated thunderstorm cells, and the maximum temperature change of the cold pool was 8℃·h-1, which only caused the localized short-time severe rainfall along the Qinling Mountains. The “7·26” thunderstorm occurred on the northwest side of the subtropical high, the warm advection development of the middle and low layers increased the unstable energy, the upwelling movement in Guanzhong Plain and the uplift effect of the topography of Beishan provided favorable dynamic conditions for the development of thunderstorms after they moved in. However, the “7·29” storm occurred on the south side of the subtropical high and the downdraft in Guanzhong Plain was not conducive to the development of convection after the storms move in. The moving direction of the “7·26” gust front was opposite to the wind direction in the bounary layer, but parallel to the average wind direction of the storm bearing layer, which was beneficial to the convection vertical development. The low-level vertical wind shear strengthened gradually, increasing synchronously with the strength of cold pool in the course of convection development. The movement direction of the “7·29” gust front was the same as the wind direction of the boundary layer, the low-level convergence was weak, and the 0-3 km wind vector difference was always less than 5 m·s-1 during the whole process, which was not conducive to the development of convection.The special terrain affected the movement direction and intensity of the cold pool. The strong southwest outflow during the “7·26” process made the cold pool move forward along the southern boundary of the plain in a narrow strip from southwest to northeast, the cold pool was concentrated and moved fast, and the strong convergence triggered the development of new convection. During the “7·29” process, the cold pool spread in the terrain transition area of the loess tableland, and the outflow of southeast wind and southwest wind split the convection. The intensity of the cold pool was constantly weakened, which was not favourable for the development of new convection.
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