黄土高原地区云垂直结构的激光雷达遥感研究

Study of Vertical Distribution of Cloud over Loess Plateau Based on a Ground-based Lidar System

获知云垂直分布的信息对全球气候变化和人工增雨作业具有重要研究意义。利用兰州大学半干旱气候与环境观测站(SACOL)地基双波段偏振激光雷达于2009年12月至2011年11月的观测资料统计了云底/云顶高度、云几何厚度和单层云、多层云在不同季节的垂直分布情况,并对所有高度范围云和6 km以上云的色比和退偏比分布进行分析。结果表明,SACOL站地区春夏秋季节分布在0～2 km的低云所占比例超过34.9%,不透明云出现的频率高达33.5%以上;而冬季主要以4～6 km的云分布居多(35.1%)且不透明云较少(7.8%);所有高度云的色比呈单峰分布且峰值集中在1.8～2.6范围内;所有高度云的退偏比呈双峰结构,结合6 km以上云退偏比的单峰结构可将0.2～0.25区间的退偏比值作为区分水相云和冰相云的判断依据。此外,边界层的发展对云垂直结构的影响使边界层云的云底高度随边界层高度的升高而升高。

Knowledge of vertical structure of cloud is very important for studying globe climate change and rainfall enhancement. Sea- sonal variation of vertical distribution of cloud geometrical properties, such as cloud base and cloud top height, cloud geometrical thick- ness, single -layer and multi - layer, color ratio and depolarization ratio of cloud were analyzed based on continuous lidar measure- ments from December 2009 to November 2011 at the Semi - Arid Climate and Environment Observatory of Lanzhou University （SACOL）. The results show that the cloud appears more than 34.9% below 2 km in spring, summer and autumn, and the frequency of the opaque cloud is up to above 33.5%, but there is more cloud （35.1%） above 4 -6 km in winter with a small amount of opaque cloud （7.8%）. Unimodal distribution was found for color ratio and the peak value concentrated at the range of 1.8 -2.6 for all cloud. But the depolarization ratio showed a bimodal distribution, furthermore, the depolarization ratio between 0. 2 and 0.25 can be used to distinguish ice cloud from water cloud for ground - based lidar in similar field of view. The height of convective boundary layer has an impact on the vertical structure of cloud, the base height of boundary cloud increases with the height of boundary layer.