The Dynamics and Energetics of Small-Scale Atmospheric Vortices

边界层涡旋，包括相对知名的尘暴，通常采取良性柱状大气涡旋的形式。人们对它的了解不如它的近亲龙卷风，但最近的证据表明，它可能比最初想象的更普遍，并且可能是边界层结构和相互作用的重要控制因素。本文对边界层涡旋，特别是沙尘暴涡旋的形成和维持进行了动力学研究。这项研究将主要是理论和数值模拟研究，但可能包括有限的观测数据采集和分析，特别是来自移动多普勒雷达的数据。和它们规模更大的亲戚一样，关于尘卷风的主要科学问题是它们自转的来源。单一的答案可能不存在。在某些情况下，可以发现垂直涡度的环境源是一种环境特征，或者它可能是局部产生的。在没有水平切变的情况下，沙尘暴中的垂直涡度可能是由水平涡度的倾斜形成的，要么是表层平均切变的倾斜，要么是局地产生的倾斜。在没有其他环境源的情况下，已存在的对流细胞及其相互作用已被证明是垂直和水平涡度的来源。这项研究将考虑所有这些可能性，但主要重点是最后一种可能性，部分原因是它在几个实验室实验和实地项目中几乎无法解释。通过抑制消散和扩散，高度螺旋形的尘卷风可以将近地表空气输送到比非旋转热气流更高的大气中。因此，它们在确定混合层的高度、控制或改变热量、动量和颗粒输运方面可能是重要的，甚至是主要的。这些能量和输运性质也将在本研究中考虑。本研究的目的总结如下：1。寻找和比较在水平或垂直风切变存在或不存在的情况下对流热气流获得旋转并成为准垂直柱状涡的机制；2. 研究与这种涡旋维持有关的能量学；3. 为了评价和比较旋转和非旋转边界层热力对热、动量和粒子的垂直输送，本研究将确定边界层涡旋形成和维持的一些必要条件。研究结果可能对龙卷风的形成机制有所启发。关于边界层涡旋在热量、动量、化学物质和微粒的输送中所起作用的知识，可能会对污染研究、危险废物管理和深对流开始的预测产生影响。＊＊＊

9727150 Lilly The boundary layer vortex, which includes the relatively well-known dust devil, generally takes the form of a benign columnar atmospheric vortex. It is less well understood than its more dramatic cousin, the tornado, but recent evidence suggests that it may be more common than originally thought and may be important as a controlling factor of boundary layer structure and interactions. An investigation is proposed of the dynamics of the initiation and maintenance of boundary layer vortices, in particular, the dust devil vortex. This research will be primarily a theoretical and numerical simulation study, but may include limited acquisition and analysis of observational data, especially from mobile Doppler radar. As with their larger scale relatives, the principal scientific question regarding dust devils is their source of rotation. A single answer probably doesn't exist. An ambient source of vertical vorticity may be found, in some cases, as an environmental feature, or it may be generated locally. In the absence of horizontal shear, the vertical vorticity in a dust devil might form from tilting of horizontal vorticity, either that of the mean shear in the surface layer or again by local generation. In absence of other environmental sources, pre-existing convective cells and their mutual interactions have been evidenced as sources of both vertical and horizontal vorticity. The study will consider all these possibilities, but the primary focus is on the last, due partly to its mostly unexplained appearance in several laboratory experiments and field projects. By inhibiting dissipation and diffusion, highly helical dust devils may transport near-surface air higher into the atmosphere than can non-rotating thermals. Thus they may be important or even dominant in establishing the height of the mixed layer, controlling or modifying heat, momentum and particulate transports. These energetic and transport properties of rotating ther mals will also be considered in this study. The objectives of the proposed research are summarized as the following: 1. To seek and compare mechanisms by which convective thermals acquire rotation and become quasi-vertical columnar vortices in either the presence or absence of horizontal or vertical wind shear; 2. To examine the energetics associated with the maintenance of such vortices; 3. To evaluate and compare the vertical transports of heat, momentum and particulates by rotating and non-rotating boundary layer thermals From this study, some necessary conditions for the formation and maintenance of boundary layer vortices will be determined. Results may shed some light on the formation mechanisms of tornadoes. Knowledge gained of the role that boundary layer vortices play in transports of heat, momentum, chemicals and particulates may have impact on /pollution studies, hazardous waste management, and the prediction of initiation of deep convection. ***