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.

夜间（Pecan）项目提升对流的移动和固定位点的观察将与分析和数值建模方法一起使用，以研究影响夜间低水平喷气机（NLLJ）的形成，进化和结构的主要物理机制。来自山核桃综合响料阵列（PISA）的数据，每个仪器（包括辐射，激光镜，辐射仪和雷达）都测量运动学和热力学轮廓的数据，都将通过使用两个移动平台进行协调扫描策略进行的湍流测量来补充。这些集成的数据集将在NLLJ与发展中的夜间稳定边界层（SBL）和中尺度干扰时相互作用时提供新颖的，整体的图片。将详细研究地形斜率，热型SBL结构，环境分层和强迫强迫对NLLJ的演变的影响，详细研究大平原的轻轻倾斜地形特征：夜间低级喷气式飞机（NLLJ）是一种大气边界层现象，通常在美国的大平原和全球许多其他地方观察到。 NLLJ通常在无云的无云条件下开始在日落周围发展，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而衰减。尽管迄今为止进行了许多理论，数值和观察性分析，这为NLLJ造成的NLLJ源于突然释放近日落的摩擦约束引起的力不平衡，但NLLJS结构和进化的许多方面仍然不太了解。文献中关于NLLJ高度和SBL顶部之间紧密关联的索赔并不能保持审查：SBL的深度通常在整个夜晚增加，而许多观察结果表明，最大值最大值通常在夜间下降，保持稳定或升高。尚不清楚地形斜率如何影响SBL和NLLJ结构之间的关系。最近的许多研究表明，在发育中的SBL与NLLJ相互作用时的湍流性质应进一步研究。关于与NLLJ相关的风能曲率对孔传播的影响，NLLJ与中尺度干扰的相互作用以及NLLJ/孔相互作用可能导致对流启动的机制。我们的研究旨在提供有关NLLJ之间相互作用，发展夜间SBL，传播中尺度骚乱和对流启动之间的相互作用的新知识。BRODER的影响：NLLJS通过提供对深度降临和巨大的巨大降水事件的动态和热力学支持，对区域天气和气候产生重大且广泛的影响对区域天气和气候的影响。它们是水分和低温层污染物的有效输送机，例如臭氧和细颗粒，以及包括真菌，孢子和昆虫在内的农业害虫。 NLLJ也会对风能产业产生重大影响，因为增强的风提供了可靠的能源来源，但是相关的风剪和湍流会损害风力涡轮转子。早晨，NLLJ动量通过对流湍流混合的向下运输可能会产生强烈而阵风的表面风，可以加剧野火并引起沙尘暴。对拟议项目中高分辨率观测值和数值模型输出的综合分析将允许改善大气模型中当前使用的SBL参数化，并可以更好地预测NLLJ及其在夜间对流启动中的作用。最先进的观察系统和高级数值模拟技术的使用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操作，模型研究，数据处理和科学分析中扮演重要角色。