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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.

在一个半可压缩非静力中尺度数值模式中，成功地再现了一次超单体风暴及其伴生的大龙卷风。该模式的计算区域为66.4 km×66.4 km×15.1 km，水平网格尺寸为70m，垂直层数为45层。这场风暴是由1977年5月20日美国俄克拉何马州德尔城附近的高空探测采用的水平均匀环境中施加的热泡引发的。在风暴上升气流和水平气流垂直切变的相互作用下，50min后，在距地面2公里处形成了一个中低压。上升的气压梯度通过水平涡度的倾斜和随后的伸展，使上升气流在2kmagl以下加速，并在1.2kmagl处产生了60min的中气旋。转动场降低了中气旋中心附近的气压，进一步加速了上升气流，使上升气流在1公里高度附近达到40m/S。另一方面，在地面附近形成了阵风锋面，从降水区流出的雨冷空气与温暖潮湿的环境气流相遇。阵风锋面伴随着水平切变产生的垂直涡度。当低层中气旋的强上升气流来到阵风锋面正上方时，垂直涡度被拉伸，形成龙卷风。因此，研究发现，超级单体龙卷风在质量上的发展方式与登陆龙卷风的方式相似，后者通常沿着中尺度锋面发展，那里的辐合和水平切变都很强。