Mechanisms for Severe Wind Production in Nocturnal and Transitioning Convection

夜间和过渡对流中强风产生的机制

• 批准号: 1442054
• 负责人: Karen Kosiba
• 金额: $ 49.72万
• 依托单位: The Center for Severe Weather Research
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-01-01 至 2018-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1442054&HistoricalAwards=false
• 关键词: Mechanisms; Severe; Wind; Production; Nocturnal

The transition from surface-based to elevated convection and the subsequent organization and evolution of mesoscale convective systems (MCSs) as the nocturnal stable boundary layer (NSBL) develops is not well understood, complicating the forecastability of severe winds. During the transition from discrete cells to an MCS, severe surface winds may be generated but the processes responsible for the onset, intensification, and cessation of these winds are uncertain. Likely the hydrometeor type, distribution, and evolution within these MCSs, as well as the evolving properties of the NSBL, environmental shear and other factors play important roles in the initiation and maintenance of intense, surface-reaching downdrafts. The research will investigate how intense-wind-causing downdrafts reach the surface in the presence of a NSBL through characterization of the MCS and transitioning-to-MCS convective system kinematics, thermodynamics and microphysics, and how these are influenced by the local environment.This study uses data from the Plains Elevated Convection at Night (PECAN) project, planned for 2015, in addition to already collected but less complete data sets from the field programs. PECAN kinematic, thermodynamic and microphysical data obtained from a large and diverse array of observing data will enable the study of initiation/transition, evolution, internal kinematics and microphysics of severe-wind-producing MCSs. Multiple-Doppler analysis will be used to quantify the 3D winds through the depth of the MCS. Internal microphysical processes will be inferred from the radar reflectivity and dual-polarization fields and surface disdrometer data. Sounding systems and wind profilers will be used to diagnose atmospheric stability, depth of the NSBL, vertical wind structure and the location of the nocturnal low-level jet (LLJ). Mobile mesonet and stationary weather stations including Pods and PISAs, will be used to quantify the strength and horizontal extent of the surface cold pool, and quantify severe winds at the surface. Intellectual Merit:The multi-platform integrated observational study will result in a better understanding of the microphysical, thermodynamic and kinematic processes underlying nocturnal MCS evolution, transition from daytime to nocturnal/MCS organization, and how these are influenced by the NSBL during severe wind events. The research will result in a better understanding of the factors leading to the occurrence (or non-occurrence) of severe nocturnal winds. This research will also provide analyses fundamental to understanding whether severe-wind producing MCSs are elevated, surfaced-based, or hybrid systems, the microphysical composition of these systems, and the kinematics of these systems before, during, and after the occurrence of severe surface winds, and how they are affected by the local environment.Broader Impacts:Analyses, results, and improved scientific understanding from the research will be made available to the modeling and forecasting communities. Improvements to numerical models and hence the forecasting of the occurrence, severity and timing of nocturnal severe-wind producing MCSs will benefit from these fine-scale observational analyses through comparison with model output and predictions. Better understanding, leading to improved forecasts will aid in mitigating the impact of these severe-wind producing events. Education of students through the development of a PECAN-specific university course focusing on radar and mesoscale observations, participation in the field phase of PECAN, and subsequent analysis efforts will help train the next generation of scientists.

随着夜间稳定边界层（NSBL）的发展，从地面对流到高空对流的转变以及随后中尺度对流系统（MCSs）的组织和演变尚不清楚，这使强风的可预测性变得复杂。在从离散单体向MCS过渡的过程中，可能会产生强烈的地面风，但导致这些风的开始、增强和停止的过程是不确定的。这些MCSs内的水成物类型、分布和演化，以及NSBL的演化特性，可能是环境切变等因素在强烈的、到达地面的下沉气流的产生和维持中起重要作用。该研究将通过MCS和向MCS过渡的对流系统运动学、热力学和微物理学的特征，以及这些如何受到当地环境的影响，来研究在NSBL存在的情况下，由强风引起的下沉气流是如何到达地面的。本研究使用了计划于2015年开展的平原夜间高架对流（PECAN）项目的数据，以及已经收集但不太完整的现场项目数据集。从大量不同的观测数据中获得的PECAN运动学、热力学和微物理数据将使研究强风力mcs的起始/过渡、演化、内部运动学和微物理成为可能。多普勒分析将用于量化通过MCS深度的三维风。内部微物理过程将从雷达反射率和双极化场以及表面畸变仪数据推断出来。探空系统和风廓线仪将用于诊断大气稳定性、非热带气旋深度、垂直风结构和夜间低空急流（LLJ）的位置。移动中网和固定气象站（包括pod和PISAs）将用于量化地表冷池的强度和水平范围，并量化地表强风。智力优势：多平台综合观测研究将更好地理解夜间MCS演变的微物理、热力学和运动学过程，从白天到夜间/MCS组织的转变，以及这些过程在强风事件中如何受到NSBL的影响。这项研究将有助于更好地了解导致夜间强风发生（或不发生）的因素。本研究还将提供基础分析，以了解产生强风的MCSs是高架系统、地面系统还是混合系统，这些系统的微物理组成，以及这些系统在强地面风发生之前、期间和之后的运动学，以及它们如何受到当地环境的影响。更广泛的影响：研究的分析、结果和改进的科学理解将提供给建模和预测界。通过与模式输出和预测的比较，这些精细尺度的观测分析将有助于改进数值模式，从而预测夜间产生强风的mcs的发生、严重程度和时间。更好地了解，从而改进预报，将有助于减轻这些强风产生事件的影响。通过开设一门以雷达和中尺度观测为重点的PECAN大学课程、参与PECAN实地阶段以及随后的分析工作来教育学生，将有助于培养下一代科学家。