Collaborative Research: Low-level Jets in the Nocturnal Stable Boundary Layer: Structure, Evolution, and Interactions with Mesoscale Atmospheric Disturbances

合作研究：夜间稳定边界层中的低空急流：结构、演化以及与中尺度大气扰动的相互作用

• 批准号: 1359698
• 负责人: Petra Klein
• 金额: $ 98.45万
• 依托单位: University of Oklahoma Norman Campus
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-08-15 至 2019-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1359698&HistoricalAwards=false
• 关键词: Collaborative; Research; Low; level; Jets

Observations from mobile and fixed sites of the Plains Elevated Convection at Night (PECAN) project will be used in conjunction with analytical and numerical modeling approaches to investigate the principal physical mechanisms affecting the formation, evolution, and structure of Nocturnal Low Level Jets (NLLJs) in relation to night-time convection. Data from the PECAN Integrated Sounding Arrays (PISA), each measuring kinematic and thermodynamic profiles with a suite of instruments (including radiosondes, lidars, radiometers, and radars) will be complemented by turbulence measurements conducted using coordinated scanning strategies with two mobile platforms. These integrated datasets will provide a novel, holistic picture of the spatial and temporal evolution of the NLLJ as it interacts with the developing nocturnal stable boundary layer (SBL) and mesoscale disturbances. The effects of terrain slope, thermal SBL structure, environmental stratification, and synoptic-scale forcing on the evolution of NLLJs over gently sloping terrain characteristic of the Great Plains will be investigated in detail, as well as the role of interactions between NLLJs and mesoscale atmospheric disturbances (gust fronts, gravity waves, bores, solitons) in the initiation and development of night-time convection.Intellectual Merit :The nocturnal low-level jet (NLLJ) is an atmospheric boundary-layer phenomenon that is commonly observed over the Great Plains of the United States and in many other locations worldwide. The NLLJ typically begins to develop around sunset under dry cloud-free conditions conducive to strong radiative cooling at the surface. It reaches peak intensity late in the night, and then decays with the onset of daytime convective mixing. Despite many theoretical, numerical, and observational analyses conducted to date, which make a strong case for the NLLJ arising from a force imbalance induced by the sudden release of the frictional constraint near sunset, many aspects of NLLJs structure and evolution are still not well understood. A claim perpetuated in the literature regarding a close association between the height of the NLLJ and the top of the SBL does not hold up to scrutiny: the depth of the SBL generally increases throughout the night while many observations indicate that wind maxima often descend, remain steady, or rise during the night. It is also not clear how the terrain slope angle influences the relationship between the SBL and NLLJ structures. A number of recent studies suggest that the nature of turbulence within the developing SBL as it interacts with an NLLJ should be further investigated. Open questions also remain concerning the impacts of wind-profile curvature associated with NLLJs on bore propagation, interactions of NLLJs with mesoscale disturbances, and the mechanisms by which NLLJ/bore interactions may lead to convective initiation. Our study aims at providing new knowledge about the interactions between the NLLJ, developing nocturnal SBL, propagating mesoscale disturbances, and convective initiation.Broader Impacts :NLLJs exert significant and wide-ranging impacts on regional weather and climate by providing dynamic and thermodynamic support for the development of deep convective storms and heavy precipitation events over the Great Plains. They are efficient conveyors of moisture and lower-tropospheric air pollutants, such as ozone and fine particulates, as well as agricultural pests including fungi, spores, and insects. NLLJs also have major impact on the wind-energy industry since the enhanced winds provide a dependable source of energy, but the associated wind shear and turbulence can damage wind-turbine rotors. The downward transport of NLLJ momentum in the morning by convective turbulent mixing may produce strong and gusty surface winds that can intensify wildfires and generate dust storms. The integrated analysis of high-resolution observations and numerical model output in the proposed project will allow improving of SBL parameterizations currently employed in atmospheric models and lead to better predictions of the NLLJ and its role in the initiation of nocturnal convection. The use of state-of-the-art observational systems and advanced numerical simulations techniques will provide a superb opportunity for student training. Both graduate and undergraduate students will play important roles during field operations, in model studies, in data processing, and in scientific analyses.

平原夜间高对流（PECAN）项目的移动和固定站点观测将与分析和数值模拟方法结合使用，以研究影响与夜间对流相关的夜间低空急流（NLLJ）形成、演化和结构的主要物理机制。来自 PECAN 集成探空阵列 (PISA) 的数据，每个都使用一套仪器（包括无线电探空仪、激光雷达、辐射计和雷达）测量运动学和热力学剖面，并将通过使用两个移动平台协调扫描策略进行的湍流测量来补充。这些综合数据集将为 NLLJ 在与发展中的夜间稳定边界层 (SBL) 和中尺度扰动相互作用时的空间和时间演化提供新颖的整体图景。将详细研究地形坡度、热 SBL 结构、环境分层和天气尺度强迫对大平原缓坡地形特征上 NLLJ 演化的影响，以及 NLLJ 和中尺度大气扰动（阵风锋、重力波、钻孔、孤子）之间的相互作用在夜间对流的引发和发展中的作用。 ：夜间低空急流 (NLLJ) 是一种大气边界层现象，在美国大平原和世界各地许多其他地方经常观察到。 NLLJ 通常在日落前后在干燥无云的条件下开始发展，有利于表面强烈的辐射冷却。它在深夜达到峰值强度，然后随着白天对流混合的开始而减弱。尽管迄今为止进行了许多理论、数值和观测分析，有力地证明了 NLLJ 是由日落附近摩擦约束突然释放引起的力不平衡引起的，但 NLLJ 结构和演化的许多方面仍然没有得到很好的了解。文献中一直存在的关于 NLLJ 高度与 SBL 顶部之间密切相关的说法经不起推敲：SBL 的深度通常在整个夜间增加，而许多观测结果表明，风力最大值经常在夜间下降、保持稳定或上升。目前还不清楚地形坡度如何影响 SBL 和 NLLJ 结构之间的关系。最近的一些研究表明，应进一步研究正在发展的 SBL 与 NLLJ 相互作用时的湍流性质。关于与 NLLJ 相关的风廓线曲率对钻孔传播的影响、NLLJ 与中尺度扰动的相互作用以及 NLLJ/钻孔相互作用可能导致对流启动的机制，也仍然存在悬而未决的问题。我们的研究旨在提供关于 NLLJ 之间相互作用的新知识，发展夜间 SBL，传播中尺度扰动和对流起始。 更广泛的影响：NLLJ 通过为大平原上的深对流风暴和强降水事件的发展提供动力和热力学支持，对区域天气和气候产生重大和广泛的影响。它们是水分和低对流层空气污染物（例如臭氧和细颗粒物）以及农业害虫（包括真菌、孢子和昆虫）的有效输送者。 NLLJ 也对风能行业产生重大影响，因为增强的风力提供了可靠的能源，但相关的风切变和湍流可能会损坏风力涡轮机转子。早晨，NLLJ 动量通过对流湍流混合向下输送，可能会产生强烈的阵风表面风，从而加剧野火并产生沙尘暴。拟议项目中对高分辨率观测和数值模型输出的综合分析将改进目前大气模型中使用的 SBL 参数化，并更好地预测 NLLJ 及其在夜间对流启动中的作用。使用最先进的观测系统和先进的数值模拟技术将为学生培训提供绝佳的机会。研究生和本科生都将在现场操作、模型研究、数据处理和科学分析中发挥重要作用。