Mesoscale Airflow over Mountains: Modeling and Observational Analysis

山脉上空的中尺度气流：建模和观测分析

• 批准号: 0137335
• 负责人: Dale Durran
• 金额: $ 49.37万
• 依托单位: University of Washington
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-05-01 至 2006-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0137335&HistoricalAwards=false
• 关键词: Mesoscale; Airflow; over; Mountains; Modeling

Mountains exert a profound influence on the weather and climate. This research is aimed at investigating two important ways in which mountain-induced circulations directly impact human activities: strong surface winds and violent low-level rotors.Strong surface winds may be generated by the interaction of the larger-scale flow with the topography through two different mechanisms, gap winds and downslope winds. Significant weather hazards and extensive property damage can occur during extreme gap-wind and downslope-wind events. Gap winds are produced when air is forced through gaps in a mountain barrier. The winds above mountain top level need not have a component perpendicular to the ridge line while the gap winds are blowing. Downslope winds, on the other hand, only occur if there is a significant cross-mountain wind component at ridge-top level. Downslope winds attain their high velocities as the flow descends from the mountain crest. In some cases there may be synergistic interactions between the gap flow through a mountain pass and downslope winds on the slopes adjacent to the pass. A goal of this research is to better understand the dynamics of gap winds, to determine those conditions under which a given large-scale flow is more suitable for the generation of gap winds or downslope winds, and to ultimately improve the forecasting of high wind events in mountainous regions.Airflow over long ridges often produces low-level vortices with horizontal axes parallel to the ridge line. These horizontal vortices, known as rotors, pose a serious hazard to commercial, military and civilian aviation. The rotor flow is often very turbulent. Some aircraft have reported undergoing extreme rolling motions (with roll angles approaching 90 degrees), and some aircraft have been lost under conditions when strong rotors were believed to have been present. Recent work by the Principal Investigator and collaborators has identified the basic source of rotation within a typical rotor. Just as the tornadoes contain embedded regions of high vorticity (suction vortices), terrain induced rotors also appear to contain localized regions of very high vorticity. At present, almost nothing is known about the maximum strength or the dynamics of these subrotors, yet they may pose the most danger to aircraft. A goal of this proposal is to develop a better understanding of the probable strength, frequency of occurrence, and the dynamics of these subrotors.Successful completion of this research can potentially lead to better forecasts of mountain-induced severe wind hazards.

山脉对天气和气候有着深远的影响。 本研究旨在调查山地引起的环流直接影响人类活动的两种重要方式：强地面风和猛烈的低空转子。强地面风可能是由较大尺度的气流与地形相互作用通过两种不同的机制产生的，即间隙风和下坡风。 在极端的间隙风和下坡风事件期间，可能会发生严重的天气危害和广泛的财产损失。 当空气被迫穿过山体屏障的缝隙时，就会产生缝隙风。 当间隙风吹时，山顶以上的风不需要具有垂直于山脊线的分量。 另一方面，只有在山脊顶部存在显着的跨山风分量时，才会出现下坡风。 当水流从山顶下降时，下坡风的速度会达到很高。 在某些情况下，穿过山口的间隙流与山口附近斜坡上的下坡风之间可能存在协同相互作用。 这项研究的目的是更好地了解间隙风的动力学，确定给定的大尺度气流更适合产生间隙风或下坡风的条件，并最终改善山区大风事件的预报。长山脊上的气流通常会产生水平轴平行于山脊线的低空涡旋。 这些水平涡流被称为旋翼，对商业、军用和民用航空构成严重危害。 转子流通常非常湍流。 据报道，一些飞机经历了极端的横滚运动（横滚角接近 90 度），并且一些飞机在据信存在强力旋翼的情况下失踪。 首席研究员和合作者最近的工作已经确定了典型转子内旋转的基本来源。 正如龙卷风包含嵌入的高涡度区域（吸力涡流）一样，地形引起的转子似乎也包含局部的高涡度区域。 目前，人们对这些副旋翼的最大强度或动力学几乎一无所知，但它们可能对飞机构成最大的危险。 该提案的目标是更好地了解这些副旋翼的可能强度、发生频率和动力学。成功完成这项研究可能会更好地预测山区引发的强风灾害。