Progressively Complex Numerical Studies of Infrasound Generated by Atmospheric Convection

最近在美国高平原地区进行的实地试验表明，严重雷暴发出的次声频率在0.1至10赫兹之间，比非恶劣天气系统强烈得多。发展中或成熟的龙卷风的不稳定运动可能是相对强信号的一个来源。这一假设促使美国国家海洋和大气管理局进行了一项实地研究，以评估次声探测在龙卷风预警中的应用。结果是有希望的，但为了提高区分涡旋信号和外来噪声的技能，有必要提高对对流风暴中产生次声的各种机制的现有知识。虽然旋涡声学的一般理论是高度发达的，但目前对发展中的龙卷风的结构和非定常运动的了解是有限的。因此，对于龙卷风的次声并没有确定的理论。此外，对对流风暴中其他流动结构或非绝热云过程产生的次声的了解还不够充分。在没有详细观测的情况下，数值模拟提供了获得缺失知识的最佳方法。这个项目将包括对日益复杂的大气对流形式产生的次声进行系统的计算研究。考虑的形式将包括干热、非降水积云、高耸积雨云和非超级单体龙卷风。确定0.1- 10hz次声的主要来源。研究了声功率（强度）和峰值发射频率随各对流系统控制参数的变化规律。灵敏度修改微物理和亚网格湍流参数化将进行检查。主要研究将使用区域大气模拟系统的完全可压缩版本进行。此外，还将研究如何将NCAR天气研究与预报模式（WRF）应用于次声研究。智力优势：本研究将探索大气模拟的新前沿：对流风暴中湍流、微物理过程和涡旋产生的次声模拟。这个项目的智力价值在于努力阐明产生可探测次声的物理过程，并阐明声发射的确切结构。研究结果将为改进目前的方法奠定基础，将观测到的排放与不断演变的风暴中的特定事件或物体联系起来。更广泛的影响：本研究的主要更广泛的影响是通过改进次声波探测方法来改进龙卷风预警的潜力，次声波探测方法旨在补充雷达系统。此外，该项目将进一步发展大气科学和航空声学工程社区之间的协同作用。

Recent field experiments in the High Plains of the United States indicate that severe thunderstorms emit infrasound at frequencies between 0.1 and 10 Hz much more intensely than non-severe weather systems. The unsteady motion of a developing or mature tornado is one likely source of the relatively strong signal. This hypothesis motivated a field study by the National Oceanic and Atmospheric Administration to evaluate the use of infrasound detection for tornado warning. The results were promising, but in order to improve the skill in distinguishing vortex signals from extraneous noise, it is essential to advance current knowledge of the various mechanisms that produce infrasound in a convective storm. Although the general theory of vortex acoustics is highly developed, current understanding of the structure and unsteady motions of a developing tornado is limited. Consequently, there is no definitive theory for tornado infrasound. Moreover, there is insufficient understanding of the infrasound that is produced by other flow structures or diabatic cloud processes within a convective storm. In the absence of detailed observations, numerical modeling provides the best method for obtaining the missing knowledge. This project will involve a systematic computational study of the production of infrasound by progressively complex forms of atmospheric convection. The forms considered will include a dry thermal, a non-precipitating cumulus, a towering cumulonimbus and a non-supercell tornado. The dominant sources of 0.1-10 Hz infrasound will be identified. The scaling of acoustic power (intensity) and peak emission frequencies with the control parameters of each convective system will be investigated. Sensitivity to modifications of microphysics and subgrid turbulence parameterizations will be examined. The principal studies will be carried out with a fully compressible version of the Regional Atmospheric Modeling System. Adaptation of the NCAR Weather Research and Forecasting model (WRF) for the purpose of studying infrasound will also be pursued. Intellectual Merit: This research will explore a new frontier of atmospheric modeling: the simulation of infrasound generated by turbulence, microphysical processes and vortices in convective storms. The intellectual merit of this project lies in the effort to elucidate the physical processes that are responsible for generating detectable infrasound, and to clarify the exact structure of the acoustic emissions. The results will build a foundation for improving current methods to connect observed emissions to specific events or objects within an evolving storm. Broader Impacts: The principal broader impact of this study is the potential for improvement of tornado warning by contributing to the refinement of infrasonic detection methods that are intended to compliment radar systems. In addition, this project will further develop a synergy between the atmospheric science and aeroacoustical engineering communities.