Preprints
https://doi.org/10.5194/egusphere-2024-707
https://doi.org/10.5194/egusphere-2024-707
15 Mar 2024
 | 15 Mar 2024
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Revisiting the evolution of downhill thunderstorms over Beijing: A new perspective from radar wind profiler mesonet

Xiaoran Guo, Jianping Guo, Tianmeng Chen, Ning Li, Fan Zhang, and Yuping Sun

Abstract. Downhill thunderstorms frequently occur in Beijing during the rainy seasons, leading to substantial precipitation. The accurate intensity prediction of these events remains a challenge, partly attributed to insufficient observational studies that unveil the thermodynamic and dynamic structures along the vertical direction. This study provides a comprehensive methodology for identifying both enhanced and dissipated downhill thunderstorms. In addition, a radar wind profiler (RWP) mesonet has been built in Beijing to characterize the pre-storm environment downstream to the thunderstorms at the mountain foot. This involves deriving vertical distributions of high-resolution horizontal divergence and vertical motion from the horizontal wind profiles measured by the RWP mesonet. A case of enhanced downhill thunderstorm on 28 September 2018 is carried out, which support the idea that the enhanced southerly flow and corresponding convergence detected by the RWP mesonet could favorably support the development of thunderstorms in the afternoon. The results also indicate that low-level convergence is an effective signal in accounting for convective maintenance. Statistical analysis based on radar reflectivity from April to September 2018–2021 have shown that a total of 63 thunderstorm events tend to be enhanced after moving into downhill and urban areas, accounting for about 66 % of the total number of downhill thunderstorm events. A critical region for intensified thunderstorms lies on the downslope side of the mountains west to Beijing. The evolution of the downhill storm is associated with the dynamic conditions over the plain compared to its initial morphology. The lifting induced by stronger westerly winds and vertical shear in the low and midlevel troposphere exerts a critical influence on the enhancement of convection. The findings underscore the significant role of RWP network in elucidating the evolution of downhill storm.

Xiaoran Guo, Jianping Guo, Tianmeng Chen, Ning Li, Fan Zhang, and Yuping Sun

Status: open (until 03 May 2024)

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  • RC1: 'Comment on egusphere-2024-707', Anonymous Referee #1, 22 Mar 2024 reply
Xiaoran Guo, Jianping Guo, Tianmeng Chen, Ning Li, Fan Zhang, and Yuping Sun
Xiaoran Guo, Jianping Guo, Tianmeng Chen, Ning Li, Fan Zhang, and Yuping Sun

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Short summary
The prediction of downhill thunderstorm (DS) remains elusive due to the lack of profiling observations. Here we propose a novel objective method to identify the DS event and its evolutions, based on which enhance and dissipated DS are discriminated. The radar wind profiler (RWP) mesonet in Beijing is used to derive areal divergence and vertical velocity, which are used to explore the DS ambient environment. These dynamic variables from RWP help explain the spatio-temporal evolution of DS.