Structure and developing mechanism of micro-scale phenomena associated with cumulonimbus clouds

积雨云微尺度现象的结构和发展机制

基本信息

批准号：
15340154
负责人：
NIINO Hiroshi
金额：
$ 10.43万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2005
项目状态：
已结题

项目摘要

A supercell storm and an associated major tornado were successfully reproduced in a semi-compressible non-hydrostatic meso-scale numerical model having a calculation domain of 66.4km × 66.4km × 15.1km, horizontal mesh size of 70m and 45 vertical levels. The storm was initiated by imposing a thermal bubble in a horizontally uniform environment that was adopted from the upper-air sounding on 20 May 1977 near Del City, Oklahoma in the United States. After 50 min from its initiation, a meso-low is formed at 2km above the ground level (AGL) as a result of the interaction between the storm updraft and the vertical shear of the horizontal flow. The upward pressure gradient accelerates the updraft below 2km AGL and produces a mesocyclone at 1.2km AGL by 60 min through tilting of horizontal vorticity and subsequent stretching. The rotation field lowers the pressure near the mesocyclone center, which further accelerates the updraft to reach 40m/s near 1km AGL. On the other hand, a gust front where rain-cooled air flowing out from a precipitating region and a warm moist environmental inflow meet is formed near the ground. The gust front is accompanied by vertical vorticity due to horizontal shear. When the strong updraft in the low-level mesocyclone comes right above the gust front, the vertical vorticity is stretched to form a tornado. A supercell tornado therefore is found to develop qualitatively in the similar way to a landspout which often develops along a meso-scale front where both convergence and horizontal shear are strong.

在计算域为66.4km×66.4km×15.1km、水平网格尺寸为70m、垂直层数为45的半可压缩非静水力中尺度数值模型中成功再现了超级单体风暴和相关的大型龙卷风。是通过在水平均匀环境中施加热气泡而发起的，该环境是 1977 年 5 月 20 日在美国俄克拉荷马州德尔城附近从高空探测中采用的开始后 50 分钟，由于风暴上升气流与水平流垂直切变的相互作用，在地面以上 2 公里处形成中低压，向上的压力梯度加速了上升气流。低于 2 公里 AGL，并通过水平涡度倾斜和随后的拉伸在 60 分钟内产生 1.2 公里 AGL 的中气旋，旋转场降低了中气旋中心附近的压力，从而进一步降低了中气旋中心的压力。在1km AGL附近，上升气流加速至40m/s。另一方面，从降水区流出的雨水冷却空气与温暖潮湿的环境流入物在地面附近形成阵风锋。水平切变产生的垂直涡度当低空中气旋的强烈上升气流到达阵风锋正上方时，垂直涡度被拉伸形成龙卷风 A。因此，人们发现超级单体龙卷风的发展方式与陆龙卷类似，陆龙卷通常沿着中尺度锋面发展，其中辐合和水平切变都很强。