Atmospheric environmental conditions for the down-slope severe convective storms from the eastern foothills of Taihang mountains to the North China plain

To improve the understanding of the atmospheric environmental characteristics of severe storms from the Taihang mountains to the North China plain, the environmental elements of 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. 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 850 hPa and 500 hPa, 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 the 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 an environment with larger vertical wind shear, pronounced mid-tropospheric dryness, and higher DCAPE values, most MTPSS successfully propagate to 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.