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

从平原夜间高空对流(山核桃)项目的流动和固定地点的观测将结合分析和数值模拟方法来研究与夜间对流有关的影响夜间低空急流(NLLJ)的形成、演变和结构的主要物理机制。来自山核桃综合探测阵列(PISA)的数据，每个都用一套仪器(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分布，将得到利用两个移动平台协调扫描战略进行的湍流测量的补充。这些综合数据集将提供一幅新的、完整的NLLJ时空演变图景，因为它与正在发展的夜间稳定边界层(SBL)和中尺度扰动相互作用。将详细研究地形坡度、热力SBL结构、环境层结和天气尺度强迫对大平原缓坡地形上NLLJ演变的影响，以及NLLJ与中尺度大气扰动(阵风锋、重力波、钻孔、孤子)之间的相互作用在夜间对流发生和发展中的作用。NLLJ通常在日落前后开始发展，在干燥的无云条件下，有利于地表强烈的辐射冷却。它在深夜达到峰值，然后随着白天对流混合的开始而衰减。尽管到目前为止已经进行了许多理论、数值和观测分析，这些分析有力地证明了NLLJ是由日落前突然释放的摩擦约束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被很好地理解。文献中关于NLLJ高度和SBL顶部之间的密切联系的说法经不起推敲：SBL的深度通常在夜间增加，而许多观测表明，最大风速经常在夜间下降、保持稳定或上升。地形坡度角如何影响SBL和NLLJ结构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，它的湍流性质应该得到进一步的研究。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/BORK相互作用可能导致对流启动的机制，也仍然是悬而未决的问题。我们的研究旨在提供关于NLLJ、夜间SBL发展、传播中尺度扰动和对流引发之间相互作用的新知识。广泛的影响：NLLJ通过为大平原地区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而广泛的影响。它们是水分和低对流层空气污染物的有效传送器，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。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可能会损坏风力涡轮机转子。早晨由对流湍流混合向下输送的NLLJ动量可能产生强烈和阵风的地面风，从而加剧野火和产生沙尘暴。拟议项目中对高分辨率观测和数值模式输出的综合分析将有助于改进目前大气模式中使用的SBL参数，并导致对NLLJ及其在启动夜间对流中的作用的更好预测。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现场作业、模型研究、数据处理和科学分析中发挥重要作用。

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.