| 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. |
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