【作者】 丁晓东；

【导师】 黄建平；

【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】 云作为地气系统水循环与辐射收支平衡的重要调节因子,能影响全球气候。与此同时,气候变化的反馈作用又直接导致云系特征的改变,这种反馈效应在干旱半干旱地区尤为突出。研究表明,云对全球能量平衡及水循环系统的影响不仅取决于其微物理特性,同时与云宏观特性的变化密切相关。而作为云系宏观特性重要的组成部分,云类型及云的垂直结构一直以来都是云气候学研究的热点。不同的云类型间宏观及微观特性差异显著,能够对地-气系统产生明显甚至完全相反的辐射效应。而云的垂直结构则能通过影响地表及大气层顶的辐射效应及大气加热率廓线进而影响到大气环流与气候系统。因此,要深入了解云在地气系统中所扮演的角色,进一步改进我们对未来气候变化的认识,就必须对云的这些特性进行有效的观测、反演和研究。基于这些考虑,本文对云的宏观特性,尤其是云类型分布及云的垂直结构特征进行了全球及区域性的研究,主要结论如下：本文首次利用2012年发布的最新卫星遥感云分类资料分析了全球四年不同云类型的变化特征。分析发现,全球平均总云分数为74.9%。层云/层积云和卷云是分布最为广泛的主导云类型,其中卷云主要分布在中低纬度带及北半球干旱半干旱地区。绝大部分洋面地区尤其中低纬附近的东部洋面地区以层云/层积云为主导；云系海陆差异最大地区位于南北纬30。附近,赤道和低纬地区中高云陆地多于洋面,低云洋面多于陆地。各种云类型昼夜差异最大的是卷云和层云/层积云。卷云赤道地区夜间云分数较白天高15%左右；层云/层积云的昼夜差异具有显著的海陆区别。中低纬地区深对流云存在显著的年际变化特征,卷云变化特征与之相似,但变化区域更为广泛。全球干旱半干旱地区主导云类型以卷云分布最为广泛,其次是高层云与高积云。其中北半球以卷云和高层云为主,南半球以卷云和高积云为主。干旱半干旱地区云分数较全球平均状态少5%-30%。差异最显著的是中低纬度Hadley环流下沉支区域,差异最小区域位于北半球高纬度地区。值得注意的是夏季东亚干旱半干旱地区总云分数显著偏多,其中卷云、高层云等均高于同纬度陆地平均值。对于各个地区云系季节变化特性方面：卷云、高积云两者的季节变化趋势较为一致,而高层云、层云/层积云变化趋势较一致。本文还对我国西北典型区域不同云类型的垂直分布、液态云水含量及有效粒子半径的特征做了相关研究。西北三个典型区域的云分数中,天山地区最大为73.4%,祁连山和黄土高原较为相似,分别为65.2%,62.8%。层状云冬春季较多,积状云夏季占主导地位,且积状云季节变化较层状云显著。祁连山和天山地区云层发展的相对高度较低且一般集中于1.5-6km之间,黄土高原地区云层能延伸到9-12km。云液态水含量随相对高度增加有显著的递减趋势,峰值一般位于近地层,最大值为夏季低层的天山和祁连山地区,平均值达0.47mg/m3。另外,本文从观测上验证了液态降水云和非降水云有效粒子半径在垂直分布上的差异：降水云有效粒子半径在低层随高度具有显著的递减趋势；非降水云则存在较弱的上升趋势。总之,本文的研究揭示了各地区云系的基本特征与一般规律并讨论了我国西北典型干干半干旱地区云系的垂直结构及云水含量的变化特征,这些特征将会对我国干旱半干旱地区相关研究提供有益参考。更多还原

【Abstract】 Clouds play in modulating the radiative energy flow within the Earth-atmosphere system and are strongly linked to the hydrological cycle. Cloud feedbacks in the Cli-mate System in turn influence the cloud characteristics. It’s pointed out that cloud can affect the energy balance of hydrological cycle. Different cloud-climate feedback mechanisms in climate models are inconsistent with each other. Cloud characteristic is one of the most uncertain factors of climate change research. Precipitation in arid and semi-arid regions depends on both the microphysical and macrophysical characteris-tics of cloud. For better understanding how cloud distribution affects the earth-atmosphere system and global climate change, powerful observation and effec-tive inversion of cloud characteristics become increasingly indispensable.The latest satellite data released in2012are used to analyze the variation of dif-ferent cloud types. It is found that the global total cloud fractions are74.9%. Global dominant cloud types are analyzed in each region, of which cirrus and stratocumulus are the most widely distributed ones. Cirrus is mainly located in equatorial regions, low latitudes and the arid and semi-arid regions of the Northern Hemisphere. While stratocumulus covers most ocean areas especially the eastern part of the ocean in low latitudes. For latitudinal distribution, the cloud fraction of cirrus, altostratus and alto-cumulus over the land is higher than that over the ocean in equatorial regions and low latitudes; the cloud fraction of stratocumulus and cumulus shows the opposite result. What’s more, cirrus and stratocumulus have significant diurnal variation. Significant interannual variations of cirrus and deep convective cloud are found in low-latitude regions.In arid and semi-arid areas, the dominant cloud types include cirrus, altostratus and altocumulus. Meanwhile, dominant cloud types differ in each region. Cloud frac-tion in arid and semi-arid areas is less than the global one by5%-30%. The most significant difference appears in the low-latitude where Hadley circulation sinks. The seasonal variations of altocumulus and cirrus are consistent with each other, so it is the same with altostratus and stratocumulus. But both trends differ slightly from re-gion to region.In addition, the combined CLOUDSAT and CALIPSO data are employed to an-alyze macro and micro vertical characteristics of different cloud types over North-western China from2007to2008. The Northwestern China has been divided into three typical regions in this study. The results show that there are more total cloud fractions in the Qilian and the Tianshan than the Loess Plateau; over these regions cumuliform clouds are more in summer and Stratiform clouds more in winter. And the Cloud vertical probability distribution function also analyzed, the peak region appears at2-6km, and cloud liquid water content shows significant seasonal variations and a decreasing trend with altitude. The maximum value is0.47mg/m3in summer in Tianshan region, which appears near the ground. The average effective particle radius of liquid cloud is8-16μm. With altitude increasing, the effective particle radius pre-sents a significant decreasing trend for precipitation clouds, while a weak increasing trend for non-precipitation clouds.In a word, by analyzing the global cloud distribution and comparing the differ-ences of cloud fraction between different arid and semi-arid regions, the basic cloud statistics and characteristics come clear. Furthermore, by focusing on the vertical structure of cloud water content, some preliminary discussions about artificial rainfall in semi-arid region of Northwest China may benefit government’s decision-making and related researches.更多还原