乌鲁木齐一次极端暴雪事件中尺度分析

Mesoscale Analysis of an Extreme Blizzard in Urumqi

利用常规资料、NCEP/GFS(0.5°×0.5°)再分析资料,结合EC细网格(0.25°×0.25°)客观分析及乌鲁木齐风廓线雷达等资料,分析了乌鲁木齐2014年12月8日极端暴雪中尺度成因及演变特点。结果表明:暴雪是在低空西北急流与中高层西南急流叠加并维持的有利环流背景下,由700hPa至地面的风切变、风速辐合、地面冷锋及地形强迫抬升等中小尺度系统共同作用造成的。降雪前期乌鲁木齐近地层有较强的逆温、风场扰动及低层东南急流,干暖盖起到了储蓄和积累能量的作用,而强降雪时冷暖空气在山前交汇,促进了斜压不稳定增长。低空西北急流对乌鲁木齐强降雪起到动力触发作用,地形强迫抬升使迎风坡维持强的垂直上升运动和中β尺度次级环流圈,低层强水汽辐合的维持为暴雪提供了充足的水汽,乌鲁木齐特殊地形对暴雪增幅作用明显。风廓线雷达资料表明降雪前后低层东南风与西北风切变明显,强降雪时段雷达探测高度达到最高,低层较强偏北风与C2n大值区相对应,水平风向风速的垂直变化对暴雪短临预报有很好的参考价值。

Using the data of conventional observation and NCEP/GFS（0.5°×0.5°）,in combination with objective analysis of EC fine-mesh（0.25°×0.25°）data and the wind profile radar data of Urumqi,the mesoscale causes and the evolution characteristics of the extreme blizzard on 8December 2014 in Urumqi are analyzed.The results show that under the background of superposing and maintaining of the northwestern low-level jet and the southern west high-level jet,the blizzard was produced by the interaction of meso-and small-scale systems such as the shear and convergence system of the wind from700 hPa to the surface,surface cold front,orographic uplift,and so on.There were significant inversion,wind disturbance,and the southeast low-level jet in the surface layer over Urumqi before the snow.The warm dry lid played a role of storing and accumulating energy.While snowing,the cold and warm air met in front of the mountains,prompting the increase of baroclinic instability.The northwest low-level jet dynamically worked as a dynamic trigger in the snowstorm.The surface orographic uplift helps maintain the strongly ascending motion and mesoscale-βsecondary circulations.Also,the maintenance of the powerful low-level water vapor convergence provided sufficient water vapor for the blizzard.Meanwhile,the special orography of Urumqi obviously contributed to the blizzard growth.On the wind profile radar,there was a clear shear of the southeast and northwest winds in the low-level layer before and after the snow,the sounding height reached the highest,and the stronger northerly low-level wind corresponded to the high value of C2 nwhen snowing heavily.For the short-term forecast of the blizzard,the horizontal wind and C2 nhave great reference value.