中文摘要：

国际卫星云气候计划（ISCCP）已经积累了20多年的持续云观测资料,提供了迄今为止最具权威的全球尺度云量信息,为全面认识全球尺度云气候特征提供了有利条件。利用长期稳定的ISCCP D2云量资料,文中系统地分析了全球尺度总云量以及高、中、低云云量的空间分布特征。结果表明,全球总云量均值为66.5（单位：%）,其中洋面71.6,陆面55.9。全球云量分布极不均衡,且海陆差异显著,洋面局部云量最高可达90,而包括南极大陆在内的所有陆面区域多为云量低值中心。高云和低云全球分布形式存在明显差异,其中陆面以高云为主,洋面低云相对较多。低云集中分布于太平洋东南部和东北部的近海岸地区以及南半球洋面,热带辐合带、南太平洋辐合带等大尺度强对流活动区内高云数量占优势。特别,在气候平均态上分离低云和高云区,并结合对NCEP再分析资料所提供环流背景场的分析,研究发现两类云所对应的垂直和水平风场具有明显的差异。高云区从低空到对流层顶为一致的强下降运动,低云区的中高层被上升气流所控制但近地面一般存在弱的上升运动。反映在水平辐散场上,两类云对应的辐散度在垂直方向上变化趋势相反,其中低云对应的典型背景场为低层辐散高空辐合。进一步考虑水汽因素,600与850hPa水汽通量散度差对低云（负差异）和高云（正差异）的云量空间分布有较好的指示意义。

英文摘要：

The International Satellite Cloud Climatology Project（ISCCP） has so far accumulated cloud observations for over two decades,presenting the advantage to ascertain climatological characteristics of global clouds.This study focuses on the geographical patterns of high,middle,low and total cloud amount（CA）,along with their seasonal variations on global scale. The total CA is found to be quite uneven,with local maximum higher than 90 and evident gradient near coastlines.The mean total CA（unit：%） is 71.6 and 55.9,over ocean and land,respectively,with a global mean of about 66.5.The zonal mean shows that the Southern midlatitudes have the maximum and Northern subtropics are covered by the minimum CA.The averaged CA over the poles is near 69,but with larger uncertainty.The oceanic CA is slightly higher during spring and summer, while it is almost changeless over land.Low-clouds mostly occur over the southeastern Pacific and northeastern Pacific near the western coast of America.The Intertropical Convergence Zone（ITCZ） and South Pacific Convergence Zone（SPCZ） are covered by quite more high-clouds,due largely to strong active convection in these areas.The areas predominated by low-clouds or high-clouds are separated for further analysis of their respective circulation features with the result that these two category clouds are corresponding to the distinctly different vertical and horizontal wind field from each other.High-clouds are associated with strong updrafts from surface to the tropopause,while low-clouds are accompanied by combination of middle-upper downdraughts with a weak boundary-layer ascending motion.The vertical variation of divergence in the low-cloud areas is just converse to that in the high-cloud areas.Similar result is found for the vertical profiles of vapor divergence,from which the difference of vapor divergence between the two levels in the lower troposhere is shown to be instructive for the spatial pattern of low-clouds as well as high-clouds.