Collaborative Research: An Observational, Modeling, and Climatological Study of Sierra Rotors

本研究的重点是研究山波诱导转子在背风的内华达州。 旋翼是强烈的低层水平涡旋，它沿沿着平行于山峰下游的轴线形成。 虽然它们对航空非常危险，但对这种现象的定量观察和理论研究很少。 因此，对转子结构和转子动力学的理解相对不完整，预测转子的能力显示出很少的技能。本研究将使用观察和数值模拟进行。 观测数据将在欧文斯山谷及其上游收集，欧文斯山谷位于内华达州南部山脉的正东部。 内华达州南部山脉的东坡是美国本土最高、最陡的准线性地形屏障。 吹过内华达州山脉的西风经常在欧文斯山谷上空产生大振幅的山波和强转子。本项目的两个主要目标是：（1）建立转子行为的定量特征，包括转子引起的山波事件的位置和频率分布，以及（2）评估当前业务中尺度模式能够可靠地预报转子出现的程度。 第一个主要目标将通过一个小型的实地实验来实现，包括在欧文斯山谷安装一系列自动气象站和风廓线仪，并发射无线电探空仪对上游气流进行采样。 支持第二个目标的数值模拟工作旨在确定模型预测中的缺陷是否（通过与观测数据的比较显示）是由于大的代表性不足，本文的研究成果将为进一步提高我国海洋预报能力提供依据。适用于陡峭地形的数值模型。 这种改进的结果之一将是更好地预报山区的严重航空危险。

This research is focused on a study of mountain-wave induced rotors in the lee of the Sierra Nevada. Rotors are intense low-level horizontal vortices that form along an axis parallel to and downstream of a mountain crest. While they are known to be very hazardous to aviation, there have been few quantitative observational and theoretical studies of this phenomenon. As a result, understanding of rotor structure and rotor dynamics is relatively incomplete, and the ability to forecast rotors shows little skill.This study will be conducted using observations and numerical simulations. The observations will be collected in and upstream of the Owens Valley, which lies directly to the east of the southern Sierra Nevada. The eastern slopes of the southern Sierra Nevada are the tallest, steepest quasi-linear topographic barrier in the contiguous United States. The westerly winds that blow across the Sierra Nevada frequently generate large-amplitude mountain waves and strong rotors over the Owens Valley.Two major objectives of this project are to: (1) establish quantitative characteristics of the rotor behavior including the location and the frequency distribution of the rotor-inducing mountain-wave events, and (2) evaluate the extent to which current operational mesoscale models can reliably forecast the occurrence of rotors. The first major objective will be accomplished with a small field experiment involving the installation of an array of automatic weather stations and wind profilers in the Owens Valley and radiosonde launches to sample the upstream flow. The numerical modeling effort in support of the second objective is designed to determine whether deficiencies in the model forecasts (as revealed by comparison with the observational data) are due to an inadequate representation of the large-scale flow striking the mountains or to difficulties in the detailed computation of the mountain waves and rotors themselves.The results of this project will serve as a basis or improving the forecasting capability of numerical models applied to steep topography. One consequence of such improvement would be to provide better forecasts of severe aviation hazards in mountainous terrain.