Disaster-causes of a cold wave snowstorm in the north slope of middle Tianshan Mountains
Based on the conventionally observational data and NCEP l°× 1° 6-hour interval reanalysis data,one snowstorm event occurred at Urumqi in the middle Tianshan Mountain,Xinjiang,China on April 2011 is comprehensively analyzed.The water vapor,upper-lower jet conditions and temperature conditions are diagnosed.The results indicate that under the stable circulation background,the enhanced 500 hPa West-Siberia trough was extended to 35°N that makes activity cold and warm air together in the low level.The atmospheric baroclinicity enhanced the Quasi-stationary front in the Tianshan maintained for a long time,resulting in the two branch frontal zones converged north-southward with a strong front control and continuing snowy weather in the north slope of Middle Tianshan Mountain.The deep moisture layer and the sustained water vapor convergence together provided plentiful water for the snowstorm;the configuration of high and low jet and development of positive vortex from lower layer to the middle of troposphere were beneficial to upper-level divergence,lower-level warm-wet air convergence and persistent increase in vertical ascending motion,which provide dynamic condition for the snowstorm.The strong storm area corresponded well to the moist potential vorticity.It is showed that the stable confrontation condition of warm and cold advection and wedging of cold air are one of the important reasons that causes snowstorm continuing and increasing,while the low-level cold air advection plays the key role for maintaining lower air temperature during the whole snowfall period.As the height of the 0 ℃-level bright zone atmospheric layer is lower than that of the 950 hPa,the character of precipitation will change from rain to snow.Furthermore,the diagnosis showed that it is the surface air temperature decreases to near freezing point rapidly that let the precipitation transit from rain to snow.
国家科技期刊平台
NSTL
万方数据
维普
