西北半干旱区激光雷达探测卷云几何特征和光学厚度

Lidar observations of spatial and temporal variations of cirrus clouds over semi-arid areas in Northwest

为了研究中国西北半干旱区卷云几何特征和光学特性的时空分布特征,利用兰州大学半干旱气候与环境观测站(SACOL,35°57′N,104°8′E)的微脉冲激光雷达(MPL-4B)探测卷云过程,分析讨论了卷云的结构、光学性质及其时间变化特征,结果表明,卷云高度分布范围为7～10 km,卷云经历了薄-厚-薄的过程,平均厚度为(2.0±0.5)km。卷云环境温度在-51℃～-39℃范围之内。卷云的光学厚度在0.084～1.649之间,光学厚度随几何厚度的增加而增大,平均光学厚度为0.651±0.403。卷云激光雷达比为(17±17)sr。薄卷云的激光雷达比要比厚卷云的大。光学厚度小于0.3的光学薄卷云出现高度在8.6 km以上,环境温度低于-45℃,几何厚度小于1.8 km,雷达比分布在5～69 sr。

In order to understand the spatial and temporal variations of cirrus over semi-arid areas in North- west of China, macrophysical and optical characteristics of cirrus clouds were observed by micro pulse lidar （MPL-4B） over Semi-Arid Climate and Environment Observatory of Lanzhou University （SACOL, 35°57′N,104°8′E）. The structures and optical properties of the cirrus clouds as well as their spatial and temporal variations were discussed and analyzed. The results show that cirrus clouds change from thin to thick, observed ranging from 7 to 10 km, with a mean thickness of （2.0 ± 0.5） km. During this period, the samples have temperature between -51℃ and -39℃. The cloud optical depth increases and then decreases with increasing geometrical depth, ranging from 0.084 to 1.649, with a mean value of 0.651 ± 0.403. Lidar ratio of cirrus clouds is （17 ~ 17） sr and it＇s found that lidar ratio of optically thin cirrus is larger than that of thick cirrus. Thin cirrus clouds with ambient temperature below -45℃ occurr above 8.6 km and its thickness is lower than 1.8 km. The lidar ratio of thin cirrus is between 5 and 69 sr.