太行山东麓强对流风暴下山的演变过程与环境大气特征的关系

The relationship between the evolution of severe storms from mountains to North China Plain and the atmospheric environmental characteristics

  • 摘要: 本文基于2011—2020年暖季期间太行山东麓568个从山区到平原的强对流风暴(MTPSS)样本,利用ERA5资料和观测探空数据,研究太行山东麓对流风暴下山的演变与东麓平原地区的环境大气特征之间的关系。结果表明,相较于华北暖季平均态(WSA),大的不稳定能量、显著深厚的湿层和大的850 hPa与500 hPa的假相当位温差环境有利于出现MTPSS事件,加之WSA较大的下沉对流有效位能(DCAPE)值和显著中层干层,表明MTPSS事件环境特征与华北雷暴大风环境特征相似。由Q矢量散度衡量的天气尺度系统强迫统计表明,天气尺度强迫越强,MTPSS成功下山概率越高。不同强迫类型下,主导MTPSS演变的环境因子不同:强强迫(SF)下风垂直切变等动力因子占主导,弱强迫(WF)下CAPE等热力因子占主导。如果不区分天气尺度系统强迫类型,成功下山事件和未成功下山事件的环境参量值差异不显著,区分天气尺度系统强迫后,SF的环境要素差异显著,WF亦有一定的区分度。SF下,成功下山事件的环境特征为大的水平风垂直切变、显著中层干层和高DCAPE值,表明具有强下沉气流的有组织风暴下山影响平原地区概率高;WF下,成功下山事件假相当位温差值较大,水汽含量高,表明湿下击暴流的环境有利于对流风暴下山影响平原地区。

     

    Abstract: 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 to the east of the Taihang Mountains, 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.

     

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