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一次飑线过程中冷池影响下的地面大风演变机理

Evolution Mechanisms of Surface Winds under the Influence of Cold Pools during a Squall Line Process

  • 摘要: 冷池作为飑线系统的关键边界层特征,其强度演变与大风的生成机制密切相关。为深入探究飑线冷池引发大风的演变机制,本文基于实况数据和WRF(The Weather Research and Forecasting Model)模式,对2022年7月26日江苏地区一次飑线过程进行数值模拟,并通过扰动蒸发过程参数设计冷池强度敏感性试验,系统研究了冷池影响下的大风演变机理。结果表明,实况中大范围冷池边界对应近地面10 m最大风速大值区。敏感性试验通过增大CONSTB参数可显著增强雨滴蒸发冷却效应,使冷池范围扩大,冷池边界平均降温4 °C,对应近地面最大风速增加2.74 m/s。冷池边界温差扩大,气压梯度攀升,冷池密度流增强,阵风锋也加强,使得地面风速增大;同时,强冷池对应更剧烈的下沉运动和低层负动力垂直加速度,强烈的下沉气流使得高层大气水平动量下传,导致近地面大风的产生和加强。

     

    Abstract: As a key boundary-layer feature of squall line systems, the evolution of cold pool intensity is closely related to the generation mechanisms of strong winds. To further investigate the evolutionary mechanisms of strong winds triggered by squall line cold pools, this study conducted a numerical simulation of a squall line event over Jiangsu on July 26, 2022, based on observational data and the WRF (Weather Research and Forecasting) model. Sensitivity experiments were designed by adjusting evaporation process parameters to systematically examine the mechanisms of wind evolution under the influence of cold pools. Results show that, in observations, extensive cold pool boundaries correspond to areas of maximum 10 m wind speed near the surface. Sensitivity experiments revealed that increasing the CONSTB parameter significantly enhances raindrop evaporative cooling, expanding the cold pool’s coverage, causing an average temperature decrease of approximately 4 °C near the cold pool boundary, and an increase of 2.74 m/s in the maximum near-surface wind speed. The temperature gradient at the cold pool boundary widens, leading to an increased pressure gradient and strengthened density current. Consequently, the gust front intensifies, resulting in higher surface wind speeds. Meanwhile, stronger cold pools correspond to more pronounced downdrafts and negative dynamical vertical acceleration in the lower layers. The intense downdrafts facilitate the downward transport of horizontal momentum from upper levels, generating and enhancing strong winds near the surface.

     

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