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基于多源资料的东北冷涡降水垂直结构分析

Analysis of the Vertical Structure of the Northeast China Cold Vortex Precipitation Based on Multisource Data

  • 摘要: 为进一步研究东北冷涡云系降水的垂直结构,本文利用布设在辽宁省阜新蒙古族自治县国家级地面观测站内的微雨雷达和激光雨滴谱仪等设备,对2020年以来阜蒙县的三次东北冷涡降水天气过程的微物理特征进行分析。结果表明:在层云稳定性降水主导的个例中,微雨雷达和雨滴谱仪测得的雨滴谱吻合程度较高,而在对流性降水较多的个例中,微雨雷达与雨滴谱仪观测的平均雨滴谱仅在中等粒子段(1~2.5 mm)表现出较好的一致性;在层云性降水阶段,较小的冰晶粒子更快的通过零度层开始融化,小液滴在零度层下方累积,出现数浓度的极值,在该极值下方,较大的冰晶粒子经历了更长的融化距离,成为较大雨滴。同时,小云滴的累积进一步促进了大云滴的收集及碰并效应的发生,利于大雨滴的形成,在零度层下方出现一个雨滴谱谱宽的极值,表现为垂直方向的雨滴谱的“凸起”,“凸起”的发生到下落发生在2~3分钟之内。垂直方向雨滴谱的拓宽在地面能否带来明显的雨强的明显增大,要取决于近地层大气中水汽含量,在辽西地区即表现为,干旱的春季,大气相对湿度较低,融化层的存在对于地面雨滴谱的拓宽无明显帮助,但在水汽相对充沛的夏季,“凸起”的下移一定程度上导致了近地层雨滴谱拓宽及雨强的增大;相对其他地区,辽西地区降水粒子数浓度偏小,但层云性降水和对流性降水的平均数浓度差别不大,质量加权直径的差异导致了雨强的差异。

     

    Abstract: Herein, to further study the vertical structure of the northeast cold vortex cloud system precipitation, the microphysical characteristics of three northeast China cold vortex precipitation events in Fuxin since 2020 are analyzed using a Micro rain radar (MRR) and laser disdrometer deployed at the national ground observation station of Fuxin Mongol Autonomous County, Liaoning Province. Results show that the raindrop size distributions (RSDs) measured by the MRR and disdrometer have high consistency in cases dominated by stable precipitation of stratus clouds and that the average RSDs only show high agreement in the medium particle size range (1–2.5 mm) in cases with a higher proportion of convective precipitation. During stratiform precipitation, the smaller ice crystal particles begin to melt faster through the 0°C layer, the small liquid droplets accumulate below the 0°C layer, and the extreme value of the droplet concentration appears. Conversely, the larger ice crystal particles experience a longer melting distance and become larger raindrops. Moreover, the accumulation of small liquid droplets below the 0 C layer further promotes the collection and collision of large droplets, which is conducive to the formation of larger raindrops. Furthermore, an extreme value of the width of RSD appears below the melting layer, manifesting as a “bulge” whose entire lifecycle, from the onset of its formation to decay, occurs within a 2–3 minute timeframe.. Whether the broadening of RSD in the vertical direction can considerably increase rainfall intensity on the ground depends on the water vapor content in the near-surface atmosphere. In the dry spring of western Liaoning, the relative humidity of the atmosphere is low, and the existing of melting layer has no obvious help for broadening the ground RSD. However, in summer, when the water vapor is relatively abundant, the downward movement of the “bulge” to a certain extent leads to the widening of the near-ground RSD and an increase in rain intensity. Compared with the number concentration of rain droplets in other regions, that in western Liaoning is smaller. Still, the average concentrations of stratus and convective precipitation are not considerably different; moreover, the difference in mass-weighted diameter of rain droplets leads to a difference in rain intensity.

     

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