Diagnosis of Three-Dimensional Ageostrophic Circulations in Upper-Level Jet-Front Systems

在对流层上部急流附近经常存在锋面或近不连续的风和温度。众所周知，这些锋面周围的垂直环流在中纬度气旋和降水系统的发展中起到了作用；然而，这种动态联系还没有完全被理解。由于高空锋面的水平和垂直尺度分别为100公里和1公里，小于探空站的平均间距，因此一直难以从探空网中提取有关锋面环流的大量信息。此外，由于锋面附近的力不处于地转平衡，简单的模型不能处理非线性复杂性，原始方程模型模拟使理解动力学变得困难。在这项资助下，凯瑟教授将把一系列近似诊断模型应用于锋面环流研究，近似水平是准地转、地转动量和平衡；原始方程模型的模拟将被视为近似模型的极限形式。这项工作的结果应该揭示高层锋面动力学的特征及其与对流层低层气旋发展的联系。

Fronts or near-discontinuities in wind and temperature frequently exist near the jet streams in the upper troposphre. It is well know that the vertical circulation around these fronts play a role in the development of midlatitude cyclones and precipitation systems; however, the dynamic link is not fully understood. Because the horizontal and vertical scales of an upper-level front, 100 km and 1 km respectively, are smaller than the average spacing of the radiosonde stations, it has always been difficult to extract much information on the frontal circulation from the radiosonde network. Also because the forces near a front are not in geostrophic balance, simple models cannot address nonlinear complexity, and primitive equation model simulations make the understanding of dynamics difficult. Under this grant Professor Keyser will apply a hierarchy of approximated diagnostic models to the study of frontal circulations, the levels of approximation being quasi-geostrophic, geostrophic momentum, and balance; simulations from primitive equation models will be treated as the limiting form of the approximated models. The results from this work should reveal the characteristics of the upper-level frontal dynamics as well as its link to the development of cyclones in lower troposphere.