Atmospheric Frontal Dynamics

大多数冬季温带地区的恶劣天气都与冷锋有关。南下暖空气和北上冷空气之间的这些过渡带代表了天气预报的重点。大多数气象服务机构使用的模式通常对这些天气系统产生准确的预报，但当它们出现错误时，部分可能与发生在低于数值模式在空间和时间上的分辨率的尺度上的运动有关。减少数值预报模型误差的一种方法是开展研究计划，以观察小尺度、高频运动，并利用这些信息通过以物理现实的方式对其影响进行参数化来引入次网格尺度效应。拟议的调查利用了从国家科学基金会部分资助的两个观测方案获得的观测结果：风暴规模业务研究气象学-锋面实验系统试验(STORM-FEST，1992)和MICROFRONTS，1995。用声波风速计和热线风速计积累了从几十公里到毫米尺度的锋面观测。一个主要目标是记录地球边界层中锋面附近的湍流动能的耗散。MICROFRONTS的数据达到了这个目的，这些数据将被用来验证与耗散过程相关的各种理论的准确性。在空间和时间上的湍流耗散过程的知识是必要的，以提供更真实的边界层耗散参数，用于预报和研究模式。第二个目标与改进经典理论模型有关，该模型为额叶收缩过程提供了物理解释，即所谓的额叶发生。这个模型忽略了在暴风雨期间观察到的锋生事件的某些特征：周期约为17小时的惯性振荡。这些振荡对锋生和伴随运动的影响将包括在理论发展中。这些解没有考虑当锋面在边界层内时变得重要的耗散过程。根据以前的研究，将耗散过程混合到理论模型中，要么粗略地处理这种影响，要么根本不处理，这是本研究的长期目标。

Most winter time severe weather in temperate latitudes is associated with cold fronts. These transition zones between warm air to the south and cold air to the north represent the focus of weather forecasts. The models used by most weather services often produce accurate forecasts of these weather systems, but errors, when they occur, may in part be associated with motions that occur on scales that are less than the resolution, in space and time, of the numerical models. One way to alleviate errors in numerical forecasting models is to carry out research programs to observe small-scale, high-frequency motions and to use this information to introduce sub-grid scale effects by parameterizing their effects in a physically realistic manner. The proposed investigation makes use of observations obtained from two observational programs that have been supported, in part, by the National Science Foundation: the Stormscale Operational Research Meteorology-Fronts Experiment Systems Test (STORM-FEST, 1992) and MICROFRONTS, 1995. Observations on the scale of fronts from tens of kilometers down to millimeter scale were accumulated by means of both sonic and hot-wire anemometers. A principal objective is to document the dissipation of turbulent kinetic energy near frontal surfaces in the Earth's boundary layer. The data from MICROFRONTS serves this purpose, and these data will be used to verify the accuracy of various theories associated with dissipative processes. Knowledge of turbulent dissipative processes, in both space and time, is necessary to provide more realistic parameterizations of boundary layer dissipation for use in forecast and research models. A second objective is associated with the improvement of a classical theoretical model that provides a physical explanation of the frontal contraction process, so-called frontogenesis. This model neglects certain features that have been observed in a frontogenesis event that occurred during STORM-FEST: inertial oscillations with periods of about 17 hours. The effect of these oscillations on frontogenesis and the accompanying motions will be included in a theoretical development. The solutions do not take account of dissipative processes that become important when the front is within the boundary layer. The blending of dissipative processes, as determined by the former investigation, into theoretical models that either handle such effects crudely or not at all, is a long-range goal of this research.***