Dynamics of the midlatitude atmosphere

在与气象学家的直接合作下，这个研究项目应用流体力学的现代数学方法来提高我们对中纬度地区（包括北美）大气天气的基本物理过程的认识。提出的工作集中在大气的两个特征上，这两个特征在我们的理论理解中存在重要的空白：对流层涡旋（高压和低压单体）的动力学，以及重力波的产生和稳定性。a)气象学家都知道，我们在北美经历的大尺度天气系统起源于对流层顶的小尺度涡度。对流层顶是一个高约10公里的过渡区，标志着大气天气产生层的顶部。这些小规模的扰动通过涡旋合并的湍流过程演变成大规模的天气结构。该研究项目旨在开发计算模型，以具体了解对流层顶涡旋的生命周期。b)重力波是大气的运动，速度更快，而且通常比控制大陆天气模式的运动规模小得多。作为一种局地现象，重力波的表现可以直接体验为“晴空乱流”，或者负责引发高寒地区降水的垂直运动。作为一种全球现象，这些波可以作为能量级联到小尺度湍流的途径，这是大气中混合和耗散的主要机制。研究人员最近在理论上发现了大尺度山波的不稳定性，并通过专门的计算机模型进一步研究了它们在大气湍流动力学中的作用。

In direct collaboration with meteorologists, this program of research applies modern mathematical methods of fluid mechanics to improve our knowledge of the basic physical processes that govern atmospheric weather in the midlatitudes (which includes North America).  The proposed work focusses on two features of the atmosphere for which there exist important gaps in our theoretical understanding: the dynamics of tropospheric vortices (high- and low-pressure cells), and the generation and stability of gravity waves. a)  It is well known to meteorologists that the large-scale weather systems we experience in North America have their origins as small-scale vorticity on the tropopause --- a transition zone about 10km high which marks the top of the weather producing layer of the atmosphere.  These small-scale disturbances evolve into large-scale weather structures via a turbulent process of vortex mergers.  This program of research seeks to develop computational models to specifically understand this lifecycle of vortices on the tropopause. b)  Gravity waves are motions of the atmosphere which are faster, and typically of much smaller scale than those governing the continental weather pattern.  As a local phenomenon, the manifestations of gravity waves are directly experienced as "clear air turbulence", or are responsible for vertical motions that trigger precipitation in alpine regions.  As a global phenomenon, these waves can serve as a pathway for energy to cascade to small-scale turbulence, which is the primary mechanism for mixing and dissipation in the atmosphere.  A recent theoretical discovery, by the researchers, of the instability of large-scale mountain waves are further investigated by specialized computer models to ascertain their role in the turbulent dynamics of the atmosphere.