2021年11月初北方极端寒潮雨雪过程及成因分析

Analysis of the characteristics and causes of the extreme rain and snow in Northern China in early November 2021

摘要:

利用多源实况和预报资料，对2021年11月5-8日我国寒潮带来的极端雨雪过程特征及成因进行全面分析，结果发现：此次过程雨雪累计量和强度在北方初冬均历史罕见，且过程持续时间长，积雪深度厚；多地降水量、降雪量和积雪深度达到或突破11月历史极值。极端强降水由异常偏强的大气斜压环境下的高空辐散、中层辐合抬升和低层近地面锋生耦合形成的持续深厚的上升运动，低空偏南急流叠加西太平洋热带扰动北侧偏东急流输送异常强盛的水汽，局部大气不稳定对流及地面气旋移动缓慢等多个因素共同造成，过程动力和水汽条件均明显大于其他雨雪过程。强降水中心的形成有区域差异，华北地区南部和黄淮地区北部、东北地区南部的强降水中心产生主要原因是大尺度动力抬升、丰沛水汽输送和不稳定对流，而内蒙古东南部强降水中心主要由大尺度降水环流形势长时间稳定维持造成。数值模式对极端降水预报有较好的预报能力，但存在一定偏差，因此过程形成原因和阈值分析对提高预报员对类似极端过程的预报有一定参考意义。

Abstract:

The characteristics and causes of the extreme rain and snow brought by strong cold wave in China from November 5 to 8, 2021 are comprehensively analyzed by using multi-source observations and forecast data. The results show that: the accumulated amount and intensity of rain and snow in Northern China were both historical rare in the early winter, meanwhile the rain and snow lasted for much a long time, with rather thick snow depth in Northeast China, the total precipitation, snowfall and snow depth in many stations reached or exceeded its historical extreme value in November. The extreme rain and snow were caused by several combined factors, one was the continuous and profound updraft coupled by high-level divergence, mid-level convergence and low-level frontogenesis under unusually strong atmospheric barocline environment, another was the unusually strong water vapor transported by the low-level southerly jet and the easterly jet near northern part of the Western Pacific tropical disturbance, the other ones were the local atmospheric unstable convection and the slow movement of surface cyclones. The dynamics and water vapor conditions are obviously stronger than most heavy rain and snow processes in Northern China. Regional differences were founded in the formation of heavy precipitation centers, the strong rain and snow centers in the southern part of North China, the northern part of Huanghuai region and the southern part of Northeast China were caused by a combination of large-scale dynamic uplift, abundant water vapor transport and unstable convection, while heavy snow centers in the southeast part of Inner Mongolia were mainly caused by long-term stable and large-scale precipitation synoptic circulation. The numerical models provided a good forecasting ability for extreme rain and snow, while the forecast deviations still existed. Therefore, this analysis of the formation causes and threshold values of the heavy rain and snow can partly give some guidance to improve the future similar forecasts in some coming extreme precipitation in Northern China.