新疆夏季对流性降水时空分布特征及成因分析

The Temporal and Spatial Characteristics of Convective Precipitation in Xinjiang among the Summer and Causes Analysis

利用1979—2016年ERA-Interim再分析数据对新疆地区夏季对流性降水的时空分布特征及环流成因开展了研究。结果表明:(1)新疆夏季降水主要集中在山区,对流性降水占总降水的比例在50%上下,在大部分盆地地区,对流性降水占比达70%以上;(2)对流性降水EOF第一模态表现为塔里木盆地西侧山区和伊犁及天山北麓的反相位变化,这种分布在21世纪00年代以前存在5年和10年左右的周期,而从1995年开始出现突变。而大范围降水塔里木盆地南侧山区和天山区域是同相位的空间型分布;(3)水汽条件和层结不稳定条件的差异共同作用导致了塔里木盆地西侧和伊犁两个地区夏季对流性降水反相位的变化。

In order to study the temporal and spatial distribution characteristics of convective precipitation and the causes of circulation in the Xinjiang area in summer,the ERA-Interim reanalysis data are utilized in this article,including precipitation products such as convective precipitation,large-scale precipitation and total precipitation,and meteorological variables such as geopotential height,relative humidity,specific humidity,temperature and winds.The results of the analysis indicate that:(1)On the characteristics of average precipitation in summer,average total precipitation and the proportion of convective precipitation show spatial distribution with the terrain.The accumulated total summer precipitation in Kunlun and Tianshan Mountains is above 200 mm on average,but for basin region it is below 40 mm.The proportion of convective precipitation in most basin region is more than 70%,while it is less than 50%for Kunlun Mountains and 50%~60%for Tianshan Mountains.(2)The Emprical orthogonal function(EOF)method is used to analyse the temporal and spatial distribution of convective precipitation in summer.The first mode from EOF analysis shows that there are a positive phase in the western moutainous area of Tarim basin and a negative phase in Ili region and the northern part of Tianshan Mountains,which indicates that the main spatial-temporal characteristic of the above two regions is anti-phase change.The time coefficients of this pattern show 5a and 10a main period before 2000s.Since 1995,there has been a sudden change,convective precipitation decreases in the west of Tarim Basin,while increases in Ili region and the northern foot of Tianshan Mountains.And this pattern is different from the first mode of large-scale precipitation which shows the same phase in the southern Tarim Basin and Tianshan Mountains.(3)On the analysis based on the anomalies of whole layer water vapour fluxes,precipitable water and geopotential heights fields,it is found that the blocking system in Eurasian mid-high latitude are stronger in typical low years of convective precipitation PC1 compared with the high years.The northern part of Xinjiang lies between the Ural Trough and the Baikal Lake high pressure,which weakens the northward water vapor transport in Xinjiang and leads to less water vapor transport across and around the Tianshan Mountains to the southern basin of Xinjiang,and more water vapor accumulates in the northern part of Tianshan Mountains.Under the background of this large-scale circulation,the vertical warming range of the lower layer in Ili region is larger and wetter than that in the western tarim basin,which makes the former's stratification instability condition stronger.The difference in both the water vapor condition and the stratification unstable condition leads to the change of the opposite phases of the convective precipitation in that two regions.