Mechanisms for Severe Wind Production in Nocturnal and Transitioning Convection

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的中尺度对流系统(MCSs)的组织和演变还没有得到很好的了解，这使得强风的预报变得更加复杂。在从离散单体到MCS的转变过程中，可能会产生强烈的地面风，但这些风的开始、增强和停止的过程是不确定的。这些MCSs内的水流星类型、分布和演化，以及NSBL的演变特性、环境切变和其他因素，可能在强烈的、到达地表的下沉气流的启动和维持中发挥着重要作用。这项研究将通过对MCS和过渡到MCS对流系统的运动学、热力学和微物理的描述，研究在NSBL存在的情况下，引起强风的下沉气流如何到达地表，以及这些如何受到当地环境的影响。这项研究使用了计划于2015年进行的平原夜间对流(Peran)项目的数据，以及已经从野外项目收集的但不太完整的数据集。从大量和多样化的观测数据中获得的山核桃运动学、热力学和微物理数据将使研究产生强风的MCSs的启动/转变、演化、内部运动学和微物理成为可能。多谱勒分析将被用来量化通过MCS深度的3D风。内部微物理过程将从雷达反射率和双极化场以及地面散射计数据中推断出来。探测系统和风廓线将用于诊断大气稳定性、NSBL深度、垂直风结构和夜间低空急流(LLJ)的位置。移动的中层网和固定的气象站，包括Pods和PISA，将被用来量化地表冷池的强度和水平范围，并量化地表的强风。智力价值：多平台综合观测研究将有助于更好地理解夜间MCS演变的微物理、热力学和运动学过程，从白天向夜间/MCS组织的转变，以及在强风事件期间NSBL如何影响这些过程。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。这项研究还将提供基本的分析，以了解产生大风的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。广泛的影响：研究的分析、结果和更好的科学理解将提供给模拟和预报团体。通过与模式输出和预测的比较，对数值模式的改进，从而对夜间产生的大风MCSs的发生、严重程度和时间的预测将受益于这些精细的观测分析。更好的理解，导致更好的预报，将有助于减轻这些强风产生事件的影响。通过开发专门针对山核桃的大学课程，侧重于雷达和中尺度观测，参与山核桃的实地阶段，以及随后的分析工作，对学生进行教育，这将有助于培训下一代科学家。

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.