一次黄河气旋新生过程中湿斜压不稳定机制的数值模拟研究  

Numerical Simulation Study of Moist Baroclinic Instability Mechanism during a Yellow River Cyclogenesis Event

作　　者：李驰钦 鲁蓉 张万诚[4] 金小霞[1,2] 高守亭 LI Chiqin;LU Rong;ZHANG Wancheng;JIN Xiaoxia;GAO Shouting(Jiangsu Meteorological Observatory,Nanjing 210041,Jiangsu,China;Key Laboratory of Transportation Meteorology,CMA,Nanjing 210041,Jiangsu,China;Nanjing Meteorological Bureau,Nanjing 210019,Jiangsu,China;Yunnan Meteorological Research Institute,Kunmin g 650034,Yunnan,China;Key Laboratory of Cloud-Precipitation Physics and Severe Storms,Institute of Atmospheric Physics,Chinese Academy of Sciences,Beijing 100029,China)

机构地区：[1]江苏省气象台,江苏南京210041 [2]中国气象局交通气象重点开放实验室,江苏南京210041 [3]南京市气象局,江苏南京210019 [4]云南省气象科学研究所,云南昆明650034 [5]中国科学院大气物理研究所云降水物理与强风暴重点实验室,北京100029

出　　处：《高原气象》2024年第3期635-654,共20页Plateau Meteorology

基　　金：国家自然科学基金面上项目(42075013);中国气象局复盘总结专项(FPZJ2023-049,FPZJ2024-047);江苏省气象局面上项目(KM202302);北极阁开放研究基金重点项目(NJCAR2018ZD02)。

摘　　要：作为温带气旋形成的主要机制,湿斜压不稳定在气旋动热力学研究中占据中心地位,其可进一步分为干斜压不稳定、湿不稳定、非绝热Rossby波和Type C气旋新生(对流层顶干侵入)四类。2016年7月18日黄河气旋快速生成后东移进入华北造成“7·20”特大暴雨,相比气旋成熟期,其初生阶段的动热力机制尚不清楚。本文利用ERA5再分析资料与WRF模式,对该气旋新生过程的湿斜压不稳定机制进行了数值模拟研究。模拟结果指出,对流层中低层呈非绝热Rossby波形态,即系统东移发展主要由垂直运动-非绝热效应的循环所推动,其中波动触发和传播所依赖的垂直运动更多由涡度平流提供;高层位涡汇与非地转风延缓了对流层顶干侵入位涡的东移,维持了高低层相位差,最终在干侵入前部发展出贯穿对流层的位涡柱。利用非线性片段位涡反演,分别从初始场中移除非平衡分量、对流层顶干侵入位涡、低层非绝热源位涡,设计了若干敏感性试验,结合广义垂直运动方程分析可得:本次过程斜压波必须在充足水汽条件下与非绝热过程耦合才能强烈发展,关闭潜热气旋新生将被抑制,干斜压不稳定无法解释本次过程;初始非平衡场的去除不影响本次斜压不稳定性质但将延后系统发展时间,受湿度条件和中尺度环流结构限制,低层非平衡风的活跃区域主要由干斜压动力学控制;该个例近地面位温梯度小,仅依赖低层初始位涡难以有效组织起非绝热Rossby波东传,同时有别于Type C气旋新生,高层位涡异常也不足以激发起强大的中低层非绝热加热。于本次黄河气旋新生而言,一方面要求初始低层位涡异常具有一定强度,以抵消高层干侵入前部伴随的冷却下沉对其的抑制;另一方面也需要高层位涡异常通过垂直渗透以涡度平流形式加强低层位涡东侧上升运动,在高低层初始相位差合适情况下,持续促使非�As the main mechanism of extratropical cyclogenesis,moist baroclinic instability plays a central role in the study of cyclone thermodynamics,which can be further divided into four categories:dry baroclinic instability,moist instability,diabatic Rossby wave and Type C cyclogenesis(tropopause intrusion).The'7·20'heavy rainstorm was caused by the eastward movement of a Yellow River cyclone into North China after its rapid formation on July 18,2016.Compared with the mature stage of the cyclone,the mechanism of the initial stage is still unclear.This article uses ERA5 reanalysis data and WRF model to study the moist baroclinic instability of the cyclogenesis event numerically.The results show that mid-lower troposphere presented diabatic Rossby wave pattern,that is,the eastward movement of the system was mainly driven by the cycle of vertical motion and diabatic effect.The vertical motion on which the wave relied was more provided by vorticity advection.The PV sink and the ageostrophic wind in the upper layer delayed the eastward movement of the tropopause intrusion PV,maintaining the phase difference between upper and lower layers.Finally,a PV column formed throughout the troposphere in front of dry intrusion.Using piecewise PV inversion,several sensitivity runs are designed to remove unbalanced circulation,tropopause dry intrusion PV and lower-level diabatic-produced PV from the initial field,respectively.Combined with the analysis of generalized omega equation,it shows that the baroclinic wave in this process must be coupled with the diabatic process with the help of sufficient water vapor to develop strongly.The cyclogenesis was suppressed when the latent heat was turned off.Dry baroclinic instability cannot explain this process.The removal of initial unbalanced field did not affect the baroclinic instability but will delay development of the system.Limited by humidity and mesoscale circulation structure,the active area of lower-level unbalanced flow was controlled by dry baroclinic dynamics.In this case,the grad

关 键 词：湿斜压不稳定 气旋新生 暴雨 位涡反演 广义垂直运动方程 

分 类 号：P447[天文地球—大气科学及气象学]