一次大气河背景下华北地区暴雨的诊断分析

利用2018年5月15—16日的ERA5再分析资料和观测资料,对大气河背景下一次华北地区暴雨过程的天气形势、大气河在暴雨过程中的作用及其在暴雨前后的演变特征以及结构特征进行了诊断分析。结果表明此次降水过程的直接影响系统是位于华北地区的高空槽、低空切变线、地面冷锋和高低空急流,这些系统使得华北地区低层辐合高层辐散,带来强烈的垂直上升运动。在有利的天气形势背景下,暴雨过程中有源于南海的大气河,经我国东南地区向华北地区延伸,核心水汽通量较强,持续时间较长,湿层十分深厚,低层高湿高能并有风速的大值区。大气河的强盛发展促使了强降水的发生,大气河逐渐减弱消散时,降水趋于结束。通过大气河的输送作用,将热带地区的暖湿水汽直接输送到华北地区,为此次暴雨的产生和维持提供了良好的水汽条件。大气河遇到泰沂山脉被迫抬升,触发强降水,地形抬升作用是此次暴雨的重要抬升机制。

Diagnostic analysis on a heavy rainfall associated with the atmospheric river in North China

Based on the ERA5 reanalysis data and observation data, the weather background of a rainstorm process occurred in North China, the role of atmospheric river during the rainstorm and its evolution characteristics and structural features before and after the rainstorm on 15-16 May,2018 were analyzed. Results show that the direct influencing systems of this precipitation process are upper trough, low-level shear line, surface cold front and high-low level jet stream in North China. Those systems cause convergence in the lower layer and divergence in the higher layer in North China, bringing intense vertical upward movement. Under advantageous synoptic background, an atmospheric river from South China Sea extends to North China through Southeast China with characteristics of strong core water vapor flux, long duration, deep wet area,the warm moist in lower layerand high wind speed area during the rainstorm.The strong development of the atmosphere river promotes the occurrence of heavy precipitation. When the atmosphere river weakens and dissipates, the precipitation tends to end. Warm and moist air from the tropics is transported directly to North China by the atmospheric river, which provids good water vapor conditions for the generation and maintenance of the rainstorm. Atmospheric river is forced to lift when meeting the Taiyi Mountains and triggered heavy precipitation. Therefore, orographic lifting is the important lifting mechanism of this rainstorm.