雨雾、雪雾共生天气气象要素分析

利用多通道微波辐射计、边界层风廓线仪及自动/人工气象站等观测资料, 分析了2007年秋冬季北京地区雨雾和雪雾两次共生天气形成与维持过程中地面和高空气象要素伴随降雨、 降雪过程的变化。结果显示:(1) 高湿和小风是雨雾、雪雾生成并造成地面低能见度的主要气象条件。大雾形成与维持过程中, 地面水平能见度与相对湿度的反相关关系非常显著。能见度越低时, 雾的含水量也越高。 (2) 较弱的降雨和降雪可以促使雾含水量减少, 提高能见度, 但降雨或降雪蒸发增湿又利于雾的维持。 (3) 雨雾在降雨过程中高层气温经历大幅增降, 除可能受天气系统影响外, 与云层中水汽凝结释放的大量潜热和含水量大幅度增加也有关系。雪雾在降雪过程中高层温度总体随着时间趋于降低且变化幅度较小。 (4) 在降雨、降雪过程中雨雾和雪雾低层一直存在水汽饱和层, 且饱和层的顶部随降雨和降雪强度的加大而抬升, 厚度不断加大, 造成地面水平能见度进一步下降。结合催化剂人工消雾与共生雾降水 (降雨或降雪) 相似的原理, 个例分析结果初步表明较弱的降雨或降雪过程对消除暖雾、冷雾的影响有限, 对改善地面水平能见度并不显著, 这对人工消雾技术研究具有一定的启发作用。

Analysis of Meteorological Elements in Rain/Snow-Mixed Fogs

Data analysis from the multi-channel microwave radiometer, boundary layer wind profiler, and auto/artificial weather station observation in Beijing region, displays those changes of surface and upper-level meteorological elements accompanied with raining or snowing processes during the formation and maintenance of two rain/snow mixed events that occurred in the autumn and the winter of 2007, respectively. The results indicate that high humidity and light wind are the main meteorological conditions in favor of fog occurrence and causing low visibility too. During the fog formation and maintenance there is a distinct inverse correlation between the horizontal visibility and surface relative humidity. The lower the visibility is, the more abundant liquid water the fog contains. Lighter rain or snow could diminish the water content and then increase the visibility within the fog. On the other hand, rain or snow evaporates and subsequently the humidification will further benefit the maintenance of the fog. In the rain-mixed fog, a significant increase/decline of the upper air temperature during the rain process is related to the released latent heat of water vapor condensation and substantial increase of water content besides the possible influence of weather systems. While in the snow-mixed fog, the upper air temperature generally declines with the time in a quite small change range. A vapor-saturated layer during the raining or snowing processes is always observed in the low layer in both the fog cases. As precipitating gets stronger, the top of the saturated layer rises higher and the layer also gets thicker, with surface horizontal visibility reduced. In regard to alike mechanism between fog dispersal and precipitation stimulation, these cases results reveal that weaker rain or snow processes have only limited effects on the dissipation of warm fogs or cold fogs, in another word, it is less conducive to increasing the surface horizontal visibility. The analysis offers some enlightenment on the effects and techniques of fog dispersal with seeding agent.