【作者】 卢昕；

【导师】 龚威； 毛飞跃；

【作者基本信息】 武汉大学 ， 摄影测量与遥感， 2022， 博士

【摘要】 气溶胶作为地球大气系统的重要组成部分,通过辐射效应来影响地-气系统的辐射和能量平衡,包括直接辐射效应和间接辐射效应两类。其中直接辐射效应是指气溶胶颗粒通过散射和吸收辐射,直接改变气候系统的辐射平衡;而间接辐射效应是指气溶胶作为云凝结核或冰核,通过改变云水含量、云光学特性以及生命期等,对地-气系统产生间接辐射影响。由于当前相关研究主要是基于被动光学卫星观测的柱积分信息,在垂直方向上对气溶胶含量和云水汽分布进行理想假设后开展的,导致气溶胶辐射效应评估具有很大的不确定性,成为全球气候变化研究中的最不确定性因素。因此,准确认识气溶胶和云的垂直分布特征,并阐明其在气溶胶辐射效应中的影响是当前亟待解决的科学问题。基于此,本论文充分发挥星载激光雷达在大尺度气溶胶和云垂向剖面观测上的优势,并联合多模式分析,对气溶胶和云的垂直不均匀性及其在气溶胶辐射效应中的影响开展深入研究。通过详细分析气溶胶的垂直分布特征,深入认识气溶胶的不同垂直分布在其直接辐射效应评估中的影响;同时发展新型的顾及云垂直分布不均匀性的云参数（云底高和云绝热率）反演算法,并将其用于气溶胶间接辐射效应的评估工作,为降低当前全球气候变化评估的不确定性提供参考。本论文的主要工作和发现如下:（1）重污染区气溶胶的垂直分布和传输特性研究。准确认识气溶胶的垂直分布特征是精确评估气溶胶直接辐射效应的关键。基于此,本研究利用十余年的CALIPSO星载激光雷达观测数据和后向轨迹追踪模型,对气溶胶种类多样、垂直分布状态复杂的中国东部气溶胶的三维宏-微观物理特性、光学特性及其来源进行了复合分析。结果表明,不同类型气溶胶的几何、光学和物理参数的空间位置和垂直分布存在显著差异,来源路径也明显不同;人为气溶胶在该区域占据主导地位,约占气溶胶总量的69%,主要分布在近地表（2公里以内）,而且气溶胶颗粒很小,接近于球形。（2）高空抬升气溶胶在气溶胶直接辐射效应中的影响评估。鉴于气溶胶在垂直方向上的不均匀性,以及高空气溶胶的强辐射效应,本研究基于CALIPSO卫星数据,并联合其他多个分析数据和模型,对重污染区中国东部高空抬升气溶胶在直接辐射效应中的影响进行了评估,量化了不同垂直分布气溶胶对辐射平衡的影响。结果显示,中国东部的抬升气溶胶层主要分布在2公里以上,甚至可以扩散至4-5公里;来自本地传输的人为污染在抬升气溶胶中占了主导作用（60%）;并导致中国东部地表入射太阳短波辐射减少了3.4 W/m²,大气稳定度平均增强0.39 K。（3）基于星载激光雷达CALIPSO的云底高反演算法研究。云垂直信息缺乏导致当前卫星云底高反演算法存在很大的局限性。针对该问题,本研究利用CALIPSO星载激光雷达垂直特征掩模产品发展了一个基于统计排序和阈值筛选策略的、不依赖绝热假设的云底高反演算法。并将样本校验方法引入到算法发展当中,通过逐步修正误差项的影响,实现了云底高的高精度反演,标准偏差仅为116米。最后获取了全球云几何参数数据集,并据此分析了云底高和几何厚度的年均、季节、昼夜和海陆分布特征。（4）卫星云绝热率反演及其在气溶胶间接辐射效应中的影响评估。云绝热率是气溶胶间接辐射效应评估的关键参数,但是由于当前高精度卫星反演云底高数据的缺失,关于云绝热率的卫星反演仍存在空白,导致气溶胶间接效应评估的高不确定性。针对此问题,本研究基于前述发展的高精度云底高反演算法及数据集,提出了一种不依赖绝热假设的卫星云绝热率反演算法,打破了云绝热率必须通过飞机观测的瓶颈,获得了全球海洋云绝热率数据集（全球平均云绝热率为0.36）,并创建了云绝热率随云内高度变化的参数方程(f_ad=-0.24?H+0.51;f_ad为云绝热率,?H为距离云底高)。同时进一步评估了云绝热率在气溶胶间接辐射效应中的影响。结果表明,当前基于绝热假设进行的云参数（云分数、云反照率和云辐射强迫）对云滴数浓度的敏感性研究存在明显高估（所有云层平均高估约10%）,而且云越厚这种高估现象越显著（厚度在600米以上的云层平均高估约25%）。更多还原

【Abstract】 Atmospheric aerosols are solid or liquid particles that are dispersed in the atmosphere.Aerosols affect the radiation and energy balance of the Earth-atmosphere system through radiation effects,which are divided into two categories:direct radiation effects of aerosols and indirect radiation effects of aerosols.The direct radiative effect of aerosols means that aerosol particles directly change the radiation balance by scattering and absorbing radiation,while the indirect radiative effect means that aerosol particles,as cloud condensation nuclei or ice nuclei,have indirect radiative effects on the climate system by changing the lifetime and optical properties of clouds.Since the current studies are mainly based on column-integrated information from passive optical satellite observations,they are carried out after making ideal assumptions about aerosol content and cloud water content distribution vertically,which leads to the large uncertainties in the assessment of direct and indirect radiative effects of aerosols and becomes the most uncertain factor in global climate change.Therefore,the accurate understanding of the vertical distribution characteristics of aerosols and clouds and the elucidation of their effects on the direct and indirect radiative effects of aerosols are urgent scientific problems to be solved.Thus,by combining multi-model analysis,this study utilizes the advantages of satellite-based lidar in large-scale aerosol and cloud vertical observation,to conduct an in-depth study on the vertical inhomogeneities of aerosols and clouds and their effects on the direct and indirect radiative effects of aerosols.By analyzing the vertical distribution characteristics of aerosols,we gain insight into the influence of different vertical distributions of aerosols in the assessment of their direct radiative effects.At the same time,we develop a novel retrieval algorithm of cloud parameters（cloud base height and cloud adiabatic fraction）considering the inhomogeneity of vertical distribution of clouds and use it in the assessment of indirect radiative effects of aerosols to provide a reference for reducing the uncertainty of the current global climate change assessment.The main contents and contributions are as follows.（1）Vertical distribution and transport properties of aerosols in the heavily polluted region.An accurate understanding of the vertical distribution characteristics of aerosols is the key to accurately assess the direct radiative effects of aerosols.Thus,based on ten years of CALIPSO observations and the backward trajectory tracking model,this study provides a composite analysis of the three-dimensional macro-microscopic physical properties,optical properties and their sources of aerosols in Eastern China,where aerosol types are diverse and vertical distribution are complex.Significant differences exist in the spatial and vertical distribution of geometric,optical,and physical parameters of aerosols.Their sources are also obviously different;anthropogenic aerosols dominate in this region,accounting for about 69%of all aerosols,mainly distributed near the surface（within 2 km）,and the aerosol particles are smaller and more spherical.（2）Assessment of the influence of elevated aerosols in the direct radiative effect.Given the inhomogeneity of aerosols in the vertical direction and the strong radiative effect of elevated aerosols,this study evaluates the influence of high-level elevated aerosols in the direct radiative effect in Eastern China based on CALIPSO observations and combined with several other analytical data and models to quantify the influence of different vertically distributed aerosols on the radiative balance.The results show that the elevated aerosols in Eastern China are mainly distributed above 2 km and can even spread to 4-5 km;anthropogenic pollution from local-transport plays a dominant role in elevated aerosols（60%）;elevated aerosols lead to a reduction of 3.4 W/m² in incident solar short-wave radiation at the surface and an average enhancement of atmospheric stability of 0.39 K in Eastern China.（3）Cloud base height retrieval based on CALIPSO.The lack of cloud vertical information leads to the great limitation of the current satellite-retrieved cloud base height.To address this problem,this study develops a cloud base height retrieval algorithm based on statistical ranking and threshold screening strategies without relying on adiabatic assumptions using CALIPSO lidar Vertical Feature Mask products.The sample calibration method is also introduced into the algorithm development,and by gradually correcting the influence of the error term,a high accuracy retrieval of the cloud base height is achieved with a standard deviation of only 116 m.Finally,the global cloud geometric data set is obtained,and the annual average,seasonal,diurnal,and land-sea distribution characteristics of cloud base height and geometric thickness are analyzed accordingly.（4）Cloud adiabatic fraction retrieval based on satellite observations and its impact on aerosol indirect radiative effects.Cloud adiabatic fraction is a key parameter for aerosol indirect effect assessment,but there is still a gap in the satellite retrieval of cloud adiabatic fraction due to the lack of high-precision satellite retrieval of cloud base height,which leads to high uncertainty in aerosol indirect effect assessment.To address this problem,this study proposes an adiabatic hypothesis-independent,satellite cloud adiabatic fraction retrieval algorithm based on the above-developed high-precision cloud base height retrieval algorithm and dataset,breaks the bottleneck that cloud adiabatic fraction must be observed by aircraft,obtains the global ocean cloud adiabatic fraction dataset,and innovatively establishes a parametric equation for cloud adiabatic fraction with the height(f_ad=-0.24?H+0.51;f_adis adiabatic fraction,?H is the height above cloud base).The effect of cloud adiabatic fraction in the aerosol indirect radiative effect is also further evaluated.The results show that the sensitivity of cloud parameters（cloud fraction,cloud albedo,and cloud radiative effect）to cloud droplet number concentration based on the adiabatic assumption is significantly overestimated（by about 10%on average）,and this overestimation becomes more significant the thicker the cloud is（average overestimation of thick clouds with geometric thickness above600 m is about 25%）.更多还原