Analysis Of Precipitation Distribution Over Xinjiang And The Dynamic Characteristics Of Meso And Micro Scale Precipitation

Xinjiang lack of water resources is located in the temperate continental arid climate zone and the temporal and spatial distribution of precipitation here is extremely uneven due to the complicated topography. In this paper, the spatial distribution characteristic of perceptible water vapor and precipitation amount in this area as well as the regulation of their variations depending on time were firstly investigated via EOF (Empirical Orthogonal Function) decomposition method with the application of NCEP daily reanalysis data with spatial resolution of2.5°×2.5°and temporal resolution of six hours per day during the period from1961to2013and PREC/L precipitation data with spatial resolution of1°×1°from1948to1948. Moreover with the knowledge of the fact that precipitation events mainly occur in summer and in the mountain in this region, the effect of the Tianshan mountains complex terrain on the evolution of heavy rainfall was thus analyzed with the simulation of a heavy rain process occurred in the mid section of the eastern Tianshan mountains in the summer of2011via the WRF (Weather Research and Forecasting Model) meso-scale numerical model and furthermore the reason of the temporal and spatial distribution of the precipitation was preliminarily discussed. Results indicated that:(1) the spatial and temporal distribution characteristics of perceptible water vapor:the temporal variability of atmospheric perceptible water in Xinjiang was small; the high value area mainly located in the Tarim basin and Junggar Basin, while the low value area mainly located in mountain regions; the amount of perceptible water is largest in summer, smallest in winter and modest in spring and autumn; the first EOF decomposition modes of four seasons present accordant variations over whole Xinjiang area, while as to the distribution feature on time scales, the modes in winter and spring could be classified to the same type and those in summer and autumn another class.(2) the spatial and temporal distribution characteristic of precipitation amount and variability: the precipitation amount over Xinjiang was small in general and that with obvious seasonal characteristics i.e. the precipitation mainly concentrated in summer and the smallest contribution of winter precipitation to annual rainfall was also investigated; the spatial distribution of precipitation amount was uneven with a reduction from northwest to southeast and that from mountain area to the basin and precipitation mainly concentrated in Ili valley, the Tianshan mountain and the Altay mountains; the EOF decomposition results of the precipitation indicated that the precipitationon spatial and temporal scales in summer and autumn were greater than those in winter and spring; a transition from dry to wet since the late1980s over Xinjiang was found but this shift was caused by an increase of precipitation in southern Xinjiang area in summer while by precipitation increasing of northern Xinjiang in winter and spring.(3) the daily variation characteristics of precipitation:the peak time of precipitation intensity and that of rainfall frequency were almost the same; the peak time of precipitation frequency appears in the middle of the night in summer and autumn while the day in winter and spring; in flood season, precipitation in the west side of the northern Tianshan mountains occurred mainly in the middle of the night, in the east side of the northern Tianshan mountains occurred mainly in the day.(4) the characteristics of local heavy rainfalkthe process of heavy precipitation in summer was the results of combined action of high and low-level jet and topographic forcing;the case study indicated that the main mechanism of the precipitation process were1)a low-level jet stream (LLJS) induced by the large-scale pattern maintained a convectively unstable environment;2) advected moist air masses at very low levels,and3)topographic convection by Tianshan mountain.