Structure of Environmental Turbulence and its Relation to Turbulent Elementary Vortices

环境湍流的结构及其与湍流基本涡的关系

基本信息

批准号：
12125201
负责人：
NIINO Hiroshi
金额：
$ 43.97万
依托单位：
Ocean Research Institute, The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research on Priority Areas
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2002
项目状态：
已结题

项目摘要

The structure and generation mechanism of large-scale elementary vortices such as tornadoes and polar lows in the atmosphere are clarified by high-resolution numerical simulations. A tornado spawned by a supercell storm is shown to develop along a gust front where verticity associated with the horizontal shear is concentrated and is further stretched by the storm updraft. Polar lows are shown to develop through baroclinic instability and latent heat release. When the baroclinicity is small a nearly axisymmetric vortex similar to a typhoon develops. When the baroclinicity is large, on the other hand, a meso-scale low accompanied with a comma-shaped cloud pattern develops. A laboratory experiment on a bathtub vortex show that the radial profile of the tangential velocity depends significantly on the characteristics of the botton boundary layer, which explains a wide variety of velocity distribution in atmospheric vorticesAlso studied are statistical characteristics of turbulence under the effect of density stratification and earth's rotation with the beta-effect by a theoretical consideration and a numerical experiment. It is shown that the density stratification tends to suppress the Rhines effect to generate zonal mean flows. A self-similar solution for a decaying divergent rotating turbulence was foundFinally, turbulent transport processes of carbon dioxide through the air-sea interface are studied by laboratory and numerical experiments. It is found that the transport is dominated by large-scale elementary vortices called surface renewal vortices and the exchange coefficient is proportional to a square root of the generation frequency of the surface renewal vortices

通过高分辨率数值模拟阐明了大气中龙卷风和极低压等大规模基本涡旋的结构和产生机制。超级单体风暴产生的龙卷风沿着阵风锋发展，其中与水平切变相关的垂直度集中，并被风暴上升气流进一步拉伸。极地低压是通过斜压不稳定性和潜热释放而形成的。当斜压较小时，会形成类似于台风的近轴对称涡旋。另一方面，当斜压较大时，会出现伴随逗号状云纹的中尺度低压。浴盆涡室内实验表明，切向速度的径向分布很大程度上取决于底部边界层的特征，这解释了大气涡旋中的各种速度分布。还研究了密度分层作用下湍流的统计特征通过理论考虑和数值实验，研究了具有β效应的地球自转。结果表明，密度分层往往会抑制莱茵效应，从而产生纬向平均流。找到了衰减发散旋转湍流的自相似解。最后，通过实验室和数值实验研究了二氧化碳通过海气界面的湍流输送过程。研究发现，传输以称为表面更新涡的大尺度基本涡为主，交换系数与表面更新涡产生频率的平方根成正比。