摘要
摘要:利用WRF模式对2016年5月2日华东地区的一次飑线过程进行数值模拟，通过开展5组不同初始云凝结核数浓度的数值试验，讨论了污染对飑线发展的影响，并用Q矢量散度进行分析，结果表明：轻度污染下飑线线状结构最完整，强对流组织形式最紧密，而污染过重或过轻均导致飑线强对流组织分散甚至断裂；轻、中度污染对飑线降水有增强作用，而污染程度过重或过轻均对降水有限制作用；从清洁大气加深到轻度污染，强回波区宽度增大，强回波的高度升高，回波强度增强，随着污染继续加深，强回波区宽度减小，强回波的高度降低，回波强度减弱；轻度污染时，垂直速度、涡度和散度的强度较强；飑前低压在轻度污染时强度最强，雷暴高压、尾流低压和冷池则是随着污染加深而逐步减弱，但重度污染时，雷暴高压、尾流低压和冷池又增强；随着污染加深，对流云区不稳定性先增强后减弱，轻度污染下不稳定性最强；除了雪粒子外，其他水凝物粒子混合比含量均在轻度污染下达到最大值，而雪粒子混合比含量的最大值是在重度污染下出现的；推导了非地转非静力平衡的Q矢量散度方程，理论分析和计算结果均表明Q矢量辐合区对应上升运动，辐散区对应下沉运动。在较清洁和轻度污染的情况下，Q矢量散度高值区最强。
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Abstract:The weather research and forecasting (WRF) model was used to simulate a squall line that occurred in East China on 2 May 2016. Through numerical experiments involving five different initial cloud condensation nuclei (CCN) concentrations, the influence of pollution on the development of the squall line was studied, and the Q vector divergence was used. The results show that under mild pollution, the linear structure of the squall line was the most complete and the strong convective structure was the most compact. Excessively heavy or too light pollution led to the dispersion and even rupture of the strong convective structure of the squall line. Moreover, light and moderate pollution levels corresponded with the strongest precipitation, while too heavy or too light pollution had a limiting effect on precipitation. With increase in the pollution level, from a clean atmosphere to light pollution, the width of the strong echo region increased, the height of the strong echo increased, and the echo intensity increased. However, with further increase in the pollution level, the width of the strong echo region decreased, the height of the strong echo decreased, and the echo intensity decreased. In the case of mild pollution, the vertical velocity, vorticity, and divergence were stronger. The intensity was the strongest under pollution; the high pressure of thunderstorm, low pressure of wake, and strength of cold pool gradually weakened as the pollution deepened, but under heavy pollution, the high pressure of thunderstorm, low pressure of the wake, and strength of cold pool were enhanced. As the pollution deepened, the instability of the flow cloud area first increased and then weakened. Under mild pollution, the instability was the strongest. Except for the snow particles, the mixing ratio of other water condensate particles reached the maximum under mild pollution, while the mixing ratio of the snow particles reached the maximum under severe pollution. The Q vector divergence equation of non-geostatic non-static equilibrium was derived. The theoretical analysis and calculation results show that the Q vector convergence area corresponds to the ascending motion, and the divergent area corresponds to the sinking motion. In the case of relatively clean and light pollution, the Q vector divergence is the strongest.



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