Collaborative Research: Constraining Volcanic Jet Dynamics with Infrasound Using Numerical and Empirical Models

爆炸性的火山喷流产生喷发柱，经常形成浮力的火山灰云，并可能完全或部分坍塌形成火山碎屑密度流，这是一种危险的快速移动的热火山灰和气体横向流动。这些自然灾害直接威胁到周边社区和全球空中交通。我们减轻这些风险的能力受到我们无法安全测量火山喷流或监测它们共同喷发的限制。次声（频率低于人类听觉的声信号）提供了一种探测距离震源数米至数千公里的火山大气振荡的方法。该项目旨在利用这些信号来约束火山喷流的物理性质，并对其进行实时测量。这些测量可以用作航空安全火山灰云预测模型的输入参数，并用于评估给定火山喷发给当地社区带来的危害。此外，这项工作将为数值和实验研究提供喷发参数和物理的约束。最近火山喷流的次声记录的频谱与人造喷流产生的声信号（喷流噪声）相似。在过去的60年里，气动声学一直在研究人造射流的流动特性与产生的声信号之间的关系。我们的长期目标是通过根据火山喷发产生的次声信号来确定火山喷流的流动特性，从而扭转这一概念。这项工作是实现这一长期目标的第一步。我们首先建立次声射流噪声观测目录，以确定特征火山射流噪声特征，并确定这些特征与已知喷发参数之间的任何相关性。这个过程包括使用新的信号处理工具和经验和理论传播建模来搜索现有的次声数据库。然后，我们将使用火山喷流的分析和数值模型，使已建立的人造喷流噪声经验模型适应火山系统。该项目由地球物理和岩石地球化学计划以及刺激竞争性研究的实验计划（EPSCoR）支持。

Explosive volcanic jets produce eruption columns that often form buoyant ash clouds and may fully or partially collapse to form pyroclastic density currents, dangerous fast-moving lateral flows of hot ash and gas. These natural hazards directly threaten surrounding communities and global air traffic. Our ability to mitigate these risks is restricted by our inability to safely measure volcanic jets or monitor them co-eruptively. Infrasound (acoustic signals with frequencies below that of human hearing) provides a means to detect the atmospheric oscillations from volcanoes at distances of meters to thousands of kilometers from the source. This project aims to use these signals to constrain the physics of volcanic jets and measurethem in real-time. These measurements may be used as input parameters for aviation safety ash-cloud prediction models and toward assessing the hazard presented to local communities by a given eruption. Additionally, this work will provide constraints on eruptive parameters and physics for numerical and experimental studies.Recent infrasound recordings of volcanic jets have frequency spectra similar to the acoustic signal produced by man-made jets (jet noise). For the past 60 years, aeroacoustics has studied the relationship between the flow properties of man-made jets and the acoustic signal produced. Our long-term objective is to reverse this concept by determining the flow properties of volcanic jets based on the infrasound signal produced by the eruption. This work represents a first step toward this long-term goal. We begin by building a catalog of infrasonic jet noise observations to determine characteristic volcanic jet noise features and determine any correlations between these features and known eruptive parameters. This process includes searching existing infrasound databases using new signal processing tools and empirical and theoretical propagation modeling. We will then use analytical and numerical models of volcanic jets to adapt established empirical models of man-made jet noise to volcanic systems.This project is supported by the Geophysics and Petrology & Geochemistry Programs and the Experimental Program to Stimulate Competitive Research (EPSCoR).