【作者】 王瑾；

【导师】 张镭；

【作者基本信息】 兰州大学 ， 大气物理学与大气环境， 2013， 硕士

【摘要】 卷云不仅通过其地气系统辐射收支效应从而对气候变化产生强烈地影响,而且在大气水循环以及对流层和平流层水汽交换中也扮演了重要的角色,但是西北半干旱地区缺乏对卷云的地基观测。利用兰州大学半干旱气候与环境观测站(SACOL,35.95°N,104.14°E)微脉冲激光雷达对中国西北半干旱中纬度地区卷云的几何和光学特征进行了观测分析,并利用辐射传输模式模拟研究了卷云的辐射效应。(1)利用微脉冲激光雷达(MPL-4B)和微波辐射计2007年4月至11月的观测数据统计分析了该地卷云特征,阐述了卷云宏观特征例如卷云高度,环境温度和几何厚度,以及云光学特征例如光学厚度,消光系数和激光雷达比。结果表明,卷云出现高度为5.8-12.7km,平均高度为9.0±1.0km。卷云几何厚度和光学厚度平均值分别为2.0±0.6km和0.394±0.267,光学厚度随几何厚度的增加呈线性增加。SACOL上空卷云主要由薄卷云和不透光卷云组成,其中不透光卷云主要出现在8-10km。卷云雷达比分布在5到70sr,平均值为22±16sr,考虑多次散射的雷达比平均值为26±16sr。薄卷云的激光雷达比大于不透光卷云的雷达比。激光雷达比随卷云光学厚度的增大呈指数减小的趋势,最大值出现在0.058-0.3之间。激光雷达比随卷云高度的增加先增加后减小,激光雷达比最大值出现在11-12km。(2)利用MPL-4B探测2007年6月1日一次卷云过程,分析讨论了卷云的结构、光学性质及其时间变化特征,并利用SBDART模式模拟研究了此次卷云过程对TOA和地面的辐射强迫特征。结果表明,卷云高度分布范围为7-10km,卷云经历了薄一厚一薄的过程,平均厚度为2.0±0.5kmm。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174±17sr。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8.6km以上,环境温度低于-45℃,几何厚度小于1.5km,雷达比分布在5-69sr。无论在TOA还是地面处,卷云短波辐射强迫均为负值,长波辐射强迫均为正值,即云短波辐射强迫对地气系统产生冷却效应,而云长波辐射强迫对地气系统产生增暖效应。无论是短波辐射强迫还是长波辐射强迫,都与卷云过程光学厚度的变化一致,当光学厚度增加,辐射强迫越大,降温/增温作用越强。当光学厚度在16：00达到最大时,云的短波和长波辐射强迫绝对值在TOA处最大值分别为51.9和59.8W/m2,在地面处最大值分别为53.8和12.8W/m2。冷却效应主要是由于卷云对短波辐射起削弱作用,削弱程度随着光学厚度的增加而增大。而增暖效应是由于光学厚度越大的卷云发射的长波辐射越多引起的。当只改变模式中云的光学厚度时发现,云短波和长波辐射强迫均与光学厚度呈线性相关,辐射强迫都随着光学厚度的增加线性增大。当光学厚度增大时,地气系统的增温速度要快于地面。对于光学厚度相同,云底高度高于8.0kmm的冰云来说,云短波辐射强迫出现“突变”,这主要是由冰晶粒子的形状,分布以及冰晶的取向引起的。更多还原

【Abstract】 Cirrus clouds play an important part in modulating regional and global climate via two complex processes, albedo effect and greenhouse effect. Additionally, cirrus clouds are crucial to the hydrological cycle of the atmosphere and to stratosphere-troposphere exchange (STE) processes for water vapor. However, the semi-arid area of northwest China is still lacking in lidar observations of cirrus clouds. Therefore, to understand the morphology and effects of cirrus clouds in this region, this study was designed to determine the statistical characteristics of cirrus clouds by using ground-based micro pulse lidar (MPL-4B) measurements at the Semi-Arid Climate Observatory and Laboratory (SACOL,35.95°N,104.1°E) of Lanzhou University in northwest China. And the radiation effect of cirrus was simulated by radiative transfer model.(1) Macrophysical and optical characteristics of cirrus clouds were investigated at SACOL using micro pulse lidar data and profiling radiometer measurements. Analysis of the measurements allowed the determination of macrophysical properties such as cirrus cloud height, ambient temperature, and geometrical depth, and optical characteristics were determined in terms of optical depth, extinction coefficient, and lidar ratio. Cirrus clouds were generally observed at heights ranging from5.8to12.7km, with a mean of9.0±1.0km. The mean cloud geometrical depth and optical depth were found to be2.0±0.6km and0.350±0.311, respectively. Optical depth increased linearly with increasing geometrical depth. The results derived from lidar signals showed that cirrus over SACOL consisted of thin cirrus and opaque cirrus which occurred frequently in the height of8-10-km. The lidar ratio varied from5to70sr, with a mean value of26±16sr, after taking into account multiple scattering effects. The mean lidar ratio of thin cirrus was greater than that of opaque cirrus. The maximum lidar ratio appeared between0.058and0.3when plotted against optical depth. The lidar ratio increased exponentially as the optical depth increased. The maximum lidar ratio fell between11and12km when plotted against cloud mid-height. The lidar ratio first increased and then decreased with increasing mid-height.(2) In order to understand the spatial and temporal variations of cirrus. The structures and optical properties of the cirrus clouds as well as their spatial and temporal variations are discussed and analyzed. Our results show that cirrus clouds change from thin to thick, observed ranging from7to10km, with a mean thickness of2.0±0.5km. During this period, the samples have temperature between -51and-39℃. The cloud optical depth increases and then decreases with increasing geometrical depth, ranging from0.084to1.649, with a mean value of0.651±0.403. Lidar ratio of cirrus clouds is17±17sr and we have found that lidar ratio of optically thin cirrus is more than that of thick cirrus. Thin cirrus clouds with ambient temperature below-45℃occurr above8.6km and its thickness is lower than1.5km. The lidar ratio of thin cirrus is between5and69sr.The cirrus shortwave radiative forcing is negative while the long-wave radiative forcing is positive no matter in TOA or on the ground, which is cloud shortwave radiative forcing has a cooling effect and long-wave radiative forcing has a warming effect to earth-atmosphere system. Both shortwave radiative forcing and long-wave radiative forcing are consistent with the changes of optical thickness of the cirrus process, when the optical thickness increases, the greater the radiative forcing, cooling./warming is stronger. When the optical thickness reaches its maximum at16:00, the absolute value of the maximum cloud shortwave and longwave radiative forcing at TOA are51.9and59.8W/m2, on the ground, the values are53.8and12.8W/n2.The cooling effect is mainly due to the cirrus weakened short-wave radiation, weaken degree increases with increasing optical thickness. Warming effect is due to the greater optical thickness, the more long-wave radiation emitted by the cirrus. When change the optical thickness of the cloud in model only, the cloud shortwave and longwave radiative forcing was linearly correlated with the optical thickness, the radiative forcing increases as the optical thickness increases linearly. When the optical thickness increases, the warming speed of the earth-atmosphere system is faster than ground. For the ice cloud with the same optical thickness and the height of the cloud base is higher than8.0km, cloud shortwave radiative forcing appears "mutation" This is mainly caused by the shape of the ice particles, distribution and orientation of ice crystals.更多还原