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

在对流层上层的急流附近，风和温度的锋或近不连续性经常存在。众所周知，这些锋面周围的垂直环流对中纬度气旋和降水系统的发展起着重要作用；然而，这种动态联系并没有被完全理解。由于高空锋的水平尺度和垂直尺度（分别为100 km和1 km）小于探空台站的平均间距，从探空台网中提取锋面环流的大量信息一直很困难。此外，由于锋面附近的力不处于地转平衡状态，简单的模型无法解决非线性复杂性，原始的方程模型模拟使动力学的理解变得困难。在这笔资助下，Keyser教授将应用一系列近似诊断模型来研究锋面环流，近似水平为准地转、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。这一工作的结果将揭示对流层低层气旋发展的高层锋面动力学特征及其联系。

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.