The Relationship between the Evolution of Severe storms from Mountains to North China Plain and the Atmospheric Environmental Characteristics

In order to improve the understanding of the relationship between the evolution of severe storms from the mountains to the plain (MTPSS) and the atmospheric environmental characteristics of the plain area east of the Taihang Mountains, the environmental elements of the 568 samples of MTPSS in the eastern foothills of the Taihang Mountains during the warm seasons from 2011 to 2020 are investigated. The study is based on ERA5 reanalysis data and radiosonde observations. The results suggest that MTPSS events in North China are closely associated with significantly enhanced environmental instability, a more substantial moisture layer, and a greater pseudo-equivalent potential temperature gradient between 850hPa and 500hPa, all of which markedly surpass the warm season average (WSA) in North China. Additionally, the common environmental conditions during WSA and MTPSS events are characterized by higher downdraft convective available potential energy (DCAPE) and marked mid-tropospheric dryness, indicating that the environmental characteristics of MTPSS events are similar to those of thunderstorm high winds in North China. Statistical analysis of synoptic-scale system forcing, assessed by Q-vector divergence, reveals that intensified synoptic-scale forcing increases the likelihood of MTPSS events successfully moving down from the mountains. The dominant environmental factors influencing MTPSS evolution differ with the intensity of the forcing: dynamic factors such as wind vertical shear prevail under strong forcing (SF), while thermodynamic factors, such as CAPE, dominate under weak forcing (WF). When synoptic-scale forcing types are not distinguished, no significant differences in environmental parameters between downhill and non-downhill events are observed. However, the differentiation of forcing types reveals significant environmental differences under SF. In environments with larger vertical wind shear, pronounced mid-tropospheric dryness, and higher DCAPE values, most MTPSS successfully propagate into the plain, indicating that organized storms with robust downdrafts are more likely to reach the plain. Under WF, downhill events exhibit larger pseudo-equivalent potential temperature differences and higher low-level moisture content compared to non-downhill events, suggesting that MTPSS are more likely to move down and influence the plain in an environment conducive to the formation of wet downbursts.