Spatial And Temporal Distributions Of Cloud Over Northwest Of China

Cloud as an important indicator of the weather and climate, plays a very important role in the radiative energy budget of the Earth’s climate system and atmospheric water vapor cycle, The changes in the macro feature (such as cloud cover, cloud height, cloud thickness, cloud water path, etc.)could have an impact on climate change. In this paper, using cloud cover, cloud water path, cloud top temperature from the ISCCP (International Satellite Cloud Climatology Project) satellite products from1990to2009, combined with the ground-base observations of temperature, precipitation, relative humidity, the cloud spatial distribution and variation in northwest China were studied. The main conclusions are as follows.The general trend of Cloud Water Path over Northwest was rising in20years with rapid fluctuations.Its spatial distribution has obvious difference in geography. Yearly averaged Cloud Water Path is increased in most parts of the Northwest. The first six eigenvectors of EOF cumulative variance contribute to87.87%, among them the first three characteristic vectors show the consistency of Cloud Water Path over20years, on average, the west negative "orthodox" and "negative" north south of different characteristics. There are overlap of multiple time scale variation of Cloud Water Path in Northwest, two of them are particularly significant within four years and seven years.The averaged total cloud amount northwest in20years was57.1%.There is a significant differences in different region in this area. The total monthly average cloud amount changed between42%and68%. The isoline of high clouds amount in east-west direction, have significant north-south differences. Cloud amount in the seasonal difference is not large, relatively high value area and relatively low basic remains the same; Cloud distribution in high clouds amount are similar, but the north greater than the south. Low cloud amount monthly changes are significantly, and in the cloud on interstate change was small, throughout the year at about24%.There is in the rate of about0.04%·a-1drop in total cloud amount. High clouds amount increased on average of the20years, the increasing rate is of0.07%·a-1.In the cloud, in contrast to the high clouds amount change trend, at the rate of0.04%·a-1.Low clouds, frequent fluctuations in the overall trend has a weak increase trend.In the whole northwest region, cloud top temperature below the southern border of northern Xinjiang, mountainous area is lower than the desert. Midwest cloud top temperature for reducing trend in Xinjiang, the biggest reduction in the China-kazakhstan border of northern Xinjiang, the overall reduction in amplitude of northern Xinjiang is greater than the southern Xinjiang. Other regions are increased in northwest China, and have more than one high value center. Relative to genting temperature can reflect the characteristics of interannual variability cloud top temperature, the change related to latitude.The correlation between the temperature and ratio of humidity at6sites in the northwest is very good. Except to the Yushu and Menyuan station, the correlation between the cloud water path and air temperature and humidity was not significant. The correlation between the total cloud amount, air temperature and humidity is better than that. In Urumqi and Dunhuang there is relatively high correlation between temperature and cloud top temperature, while in the remaining four sites the correlation between the humidity and cloud top temperature are more significantly.