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.

平原夜间高架对流（PECAN）项目移动和固定站点的观测数据将与分析和数值模拟方法相结合，研究影响夜间低空急流（NLLJs）形成、演变和结构的主要物理机制。PECAN综合探测阵列（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，将与两个移动平台使用协调扫描策略进行的湍流测量相补充。这些综合数据集将为NLLJ与发展中的夜间稳定边界层（SBL）和中尺度扰动相互作用的时空演变提供一幅新颖、全面的图景。本文将详细研究地形坡度、SBL热结构、环境分层和天气尺度强迫对大平原缓坡地形nllj演变的影响，以及nllj与中尺度大气扰动（阵风锋、重力波、孔、孤子）之间的相互作用在夜间对流形成和发展中的作用。知识价值：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上许多其他地方都能观测到。NLLJ通常在日落前后在干燥无云的条件下开始发展，有利于地面的强辐射冷却。它在深夜达到峰值强度，然后随着白天对流混合的开始而衰减。尽管迄今为止进行的许多理论、数值和观测分析都有力地证明了NLLJ是由日落后摩擦约束的突然释放引起的力不平衡引起的，但NLLJ的结构和演化的许多方面仍然没有得到很好的理解。文献中关于NLLJ高度和SBL顶部之间密切联系的说法是站不住脚的：SBL的深度通常在夜间增加，而许多观测表明，风最大值经常在夜间下降，保持稳定或上升。地形坡度角如何影响SBL和NLLJ构造之间的关系也不清楚。最近的一些研究表明，当发展中的SBL与NLLJ相互作用时，湍流的性质应该进一步研究。与NLLJ相关的风廓线曲率对孔洞传播的影响，NLLJ与中尺度扰动的相互作用，以及NLLJ/孔洞相互作用可能导致对流起始的机制等问题仍然存在。我们的研究旨在提供有关NLLJ、夜间SBL发展、中尺度扰动传播和对流起始之间相互作用的新知识。更广泛的影响：nllj通过为大平原地区深层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而广泛的影响。它们是水分和对流层低层空气污染物（如臭氧和细颗粒物）以及包括真菌、孢子和昆虫在内的农业害虫的有效传送带。nllj对风能行业也有重大影响，因为增强的风提供了可靠的能源，但相关的风切变和湍流会损坏风力涡轮机转子。NLLJ动量在早晨通过对流湍流混合向下输送，可能会产生强烈的地面阵风，从而加剧野火和产生沙尘暴。在提议的项目中，对高分辨率观测和数值模式输出的综合分析将改进目前在大气模式中使用的SBL参数化，从而更好地预测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极好的机会。研究生和本科生都将在野外作业、模型研究、数据处理和科学分析中发挥重要作用。