Structure of Environmental Turbulence and its Relation to Turbulent Elementary Vortices

通过高分辨率数值模拟，阐明了大气中龙卷风、极低压等大尺度元涡的结构和生成机制。由超级单体风暴产生的龙卷风被证明是沿着阵风锋发展的，在阵风锋处，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和潜热释放发展起来的。当斜压性较小时，发展出类似台风的近轴对称涡旋。当斜压性较大时，伴随着逗点云型的中尺度低压发展。通过浴缸涡的实验研究表明，切向速度的径向分布与底部边界层的特性密切相关，从而解释了大气涡旋中各种各样的速度分布，并从理论上和数值试验上研究了在密度层结和地球自转的β效应作用下湍流的统计特性。结果表明，密度分层倾向于抑制莱茵效应，产生纬向平均流。最后，通过实验室和数值模拟研究了CO2通过海-气界面的湍流输运过程。结果表明，输运过程主要由大尺度的基本涡--表面更新涡所控制，交换系数与表面更新涡产生频率的平方根成正比

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