Diurnal Evolution and Structure of Long-Lived Mesoscale Convective Vortices along the Mei-Yu Front over the East China Plains
Diurnal Evolution and Structure of Long-Lived Mesoscale Convective Vortices along the Mei-Yu Front over the East China Plains
复制标题
华东平原梅雨锋长寿命中尺度对流涡旋的日演化与结构
DOI：
10.1175/jas-d-17-0197.1
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发表时间：
2018
影响因子：
3.1
通讯作者：
Sun Jianhua
中科院分区：
文献类型：
--
作者：
Zhang Yuanchun;Zhang Fuqing;Davis Christopher A;Sun Jianhua
通过30天半理想化模拟的综合分析，研究了华东平原典型夏季梅雨锋沿线的长期向东传播的中尺度对流涡旋（MCV）的结构和日演化。通过对 2007 年 7 月 1 日至 10 日期间重复出现的 MCV 事件进行分析，模拟使用的横向边界条件仅随时间变化。因此，在模拟过程中，对流和涡度的行为每天都遵循紧密重复的昼夜周期。在四川盆地增强涡度异常向东延伸的协助下，初期MCV于早晨在华中山脉紧邻的背风面（东部）上空形成（第一阶段）。从当地下午到傍晚，随着MCV在平原上移动，山地-平原螺线管白天向下分支的对流减弱。这使得涡流的上层和下层部分部分解耦，并使对流转移到表面涡流的东南偏东侧（第 2 阶段）。日落之后，由于辐射强迫和增强的低空急流的结合造成的湿润和不稳定，低空 MCV 中心上方的对流立即重新活跃。这将 MCV 强化至成熟（第 3 阶段）。成熟的MCV最终演变成闭塞性亚天气气旋，在第二天早上沿华东沿海平原低层涡中心所有区域产生强对流，然后移向近海（第四阶段）。
The structure and diurnal evolution of long-lived, eastward-propagating mesoscale convective vortices (MCVs) along typical summertime mei-yu fronts over the east China plains are investigated through composite analysis of a 30-day semi-idealized simulation. The simulation uses lateral boundary conditions that vary only diurnally in time using analyses of recurring MCV events during 1–10 July 2007. Hence, the behavior of convection and vorticity follows a closely repeating diurnal cycle for each day during the simulation. Assisted by the eastward extension of enhanced vorticity anomalies from the Sichuan basin, the incipient MCV forms in the morning hours over the immediate lee (east) of the central China mountain ranges (stage 1). From local afternoon to early evening, as the MCV moves over the plains, convection weakens in the daytime downward branch of the mountain–plains solenoid. This allows the upper-level and lower-level portions of the vortex to partially decouple, and for convection to shift to the east-southeast side of the surface vortex (stage 2). Immediately after sunset, convection reinvigorates above the low-level MCV center as a result of moistening and destabilization from a combination of radiative forcing and an intensified low-level jet. This intensifies the MCV to maturity (stage 3). The mature MCV eventually evolves into an occluding subsynoptic cyclone with strong convection across all sectors of the low-level vorticity center during the subsequent day’s morning hours along the east China coastal plains before it moves offshore (stage 4).