Mesoscale Airflow Over Mountains: Orographic Drag and Upstream Convective Initiation

山脉上空的中尺度气流：地形阻力和上游对流引发

• 批准号: 0836316
• 负责人: Dale Durran
• 金额: $ 61.75万
• 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: 2008
• 资助国家: 美国
• 起止时间: 2008-12-01 至 2012-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0836316&HistoricalAwards=false
• 关键词: Mesoscale; Airflow; Over; Mountains; Orographic

Mountains exert a profound influence on the weather and climate. This project will investigate two important aspects of the interaction between mountains and the atmosphere. The first will be to examine how the drag exerted by mountains on an air stream is distributed among different vertical levels in the atmosphere and how that drag feeds back on the larger scale flow. The second effort will examine the circumstances in which low-level blocking can trigger deep convective thunderstorms upstream of a mountain and how the resulting convection evolves in the presence of the mountain and a time-varying large-scale flow. Intellectual Merit: When an air stream encounters a mountain barrier, mountain waves may be set up above and downstream of the barrier and the low-level flow may be blocked and diverted around the flanks of the mountain. These disturbances are too small in scale to be resolved in global weather and climate models, but they produce an important drag on the large-scale flow that must be parameterized. This project will attempt to place such parameterizations on a firmer theoretical footing and also determine the large-scale responses to orographic drag through the analysis of high-resolution numerical simulations. Similar high-resolution simulations will be conducted to examine the conditions under which a moist air stream blocked by a mountain can undergo sufficient low-level destabilization and lifting to trigger deep convection upstream of the mountain itself. The resulting thunderstorms are inherently non-steady, and we will examine their onset and decay in time varying large-scale flows. Such upstream convective triggering is thought to be a significant factor in regulating the distribution of precipitation in the south Asian monsoon. The Principal Investigator also will examine the influence of thermally driven circulations on the generation of these convective events. Broader Impacts: The research and professional development of two graduate students will be supported. Results should help improve the parameterization of low-level gravity wave drag in large-scale models essential for global weather forecasting and much climate research. Global climate models suggest there will be shifts in winds and moisture fluxes in response to global warming, but the resolution of those models is too coarse to allow them to directly simulate changes in the convection. Therefore, understanding the role played by mountains in triggering deep convection, both in the south Asian monsoon and in other regions, will be helpful in the management of water resources as the climate warms.

山对天气和气候产生了深远的影响。该项目将研究山脉与大气之间相互作用的两个重要方面。第一个是检查山脉在空气流上施加的阻力如何分布在大气中的不同垂直水平之间，以及该阻力如何以更大的流量为单位。第二次努力将研究低水平阻塞可以引发山上上游的深对流雷暴的情况，以及在山的存在以及随时间变化的大规模流动的情况下，所产生的对流如何演变。 知识分子的优点：当空气流遇到山区屏障时，山脉可能会在障碍物的上方和下游设置，并且低级流程可能会被阻塞并转移到山的侧面。 这些干扰的规模太小，无法在全球天气和气候模型中解决，但是它们会对必须进行参数化的大规模流动产生重要的阻力。 该项目将尝试将这种参数化放置在更牢固的理论基础上，并通过分析高分辨率数值模拟的分析来确定对地形阻力的大规模响应。 将进行类似的高分辨率模拟，以检查山区堵塞的潮湿空气流可以进行足够的低水平不稳定并抬起以触发山本身上游的深对流。 由此产生的雷暴本质上是非态的，我们将检查它们的发作和衰变，随着大规模流动而变化。 这种上游对流触发被认为是调节南亚季风降水分布的重要因素。 主要研究者还将检查热驱动循环对这些对流事件的产生的影响。 更广泛的影响：将支持两名研究生的研究和专业发展。 结果应有助于改善对全球天气预测和大量气候研究至关重要的大规模模型中低级重力波阻力的参数化。 全球气候模型表明，响应全球变暖的风和水分通量会发生变化，但是这些模型的分辨率太粗糙，无法直接模拟对流中的变化。 因此，了解山脉在南亚季风和其他地区引发深层对流中所扮演的角色将有助于水资源的管理，因为气候温暖。