新疆三大山区云的垂直分布特征初探

A Preliminary Study of Vertical Distribution of Clouds over Three Major Mountains in Xingjiang

云高不仅可以为飞机播云高度提供参考,还是研究云水资源和天气气候的重要参数。新疆山区的面积约占其总面积的40%,山区降水是其河川径流的主要来源,承载着新疆年平均总降水量的84.3%。但是山区云观测资料严重缺乏,给云的定量研究造成了很大困难。本文利用美国宇航局(NASA)卫星CloudSat的云廓线雷达(CPR)2007年1月-2008年12月的2B CLDCLASS资料,对比分析了阿尔泰山、天山和昆仑山的高、中、低云云顶和云底高度的季节和年变化特征。结果表明,三大山区中,高云、中云和低云的平均云顶和云底高度以昆仑山区为最高,天山山区次之,阿尔泰山区最低,且三大山区的高云云顶高度差别不是很大,但低云差别较大;三大山区云顶和云底高度存在不同程度的季节和年变化,其中昆仑山区变化幅度最大,低云的季节变化幅度相对于高云和中云较小;对于各山区同一种云来说,云顶和云底高度夏季达到最高,冬季降到最低;从频数来看,阿尔泰山区的云顶和云底高度主要出现在5～9km、天山山区在5～10km,昆仑山区主要出现在6～10km范围内。

Lack of water resources has been an increasingly serious constraint for societal and economic development of Xinjiang, which is located in arid and semi-arid inland areas in northwestern China and covers an area of 1,664,900 km2. Mountainous areas cover 40 % of Xinjiang. Precipitation over the mountains is the original source of rivers, contributing 84.3% to the yearly average precipitation of Xinjiang. Precipitation enhancement is considered an important way to complement traditional water resources exploration by the government and meteorological societies in recent years. Clouds play a significant role in the operation of precipitation enhancement. Cloud water resources over mountainous areas are relatively rich. Studies on vertical distribution of the clouds seem to be inadequate due to limited ground-based observations. In this study, the main regions of interest are the Tianshan, Kunlun, and Altai mountainous regions. Cloud height can reflect the development of convection in clouds, the types of clouds, and their ability to produce precipitation, thereby being important for enhancing precipitation operation, cloud water resources, and weather and climate research. Using 2B CLDCLASS data from January 2007 to December 2008 observed by the cloud profile radar （CPR） onboard the NASA＇ s CloudSat satellite, seasonal and annual variations in cloud top height and cloud base height of high, middle, and low level clouds over the Altay, Tianshan, and Kunlun mountainous regions in Xinjiang were examined. Results show that among the three mountain ranges, the highest average cloud top height and cloud base height of high, middle, and low level clouds appear in the Kunlun Mountains, followed by the Tianshan Mountains; the Altay Mountains show the lowest heights. There are slight differences among the cloud top heights of high level clouds but among those of low level clouds the differences are relatively obvious over the three mountain ranges. Seasonal and annual changes in cloud top and base heights over those three mountainous regions vary greatly, with showing the maximum amplitude over the Kunlun Mountains. Compared with high and middle level clouds, seasonal and annual changes in low level clouds are relatively small. For the same category of clouds for each mountainous region, cloud top height and cloud base height were found to peak in summer and be lowest in winter. According to the analysis of occurrence, the cloud top height and cloud base height are mainly within 9-10 km over the Altay Mountains, 5-10 km over the Tianshan Mountains, and 6-10 km over the Kunlun Mountains.