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，这些喷发柱经常形成漂浮的火山灰云，并可能完全或部分坍塌，形成火山碎屑密度流，即危险的快速移动的炽热火山灰和气体的横向流动。这些自然灾害直接威胁到周边社区和全球空中交通。我们无法安全地测量火山喷流或监测它们的共同喷发，这限制了我们缓解这些风险的能力。次声(频率低于人类听觉的声学信号)提供了一种手段，可以探测距离震源几米至数千公里的火山的大气振荡。该项目旨在利用这些信号来约束火山喷流的物理特性，并对其进行实时测量。这些测量可以用作航空安全灰云预测模型的输入参数，并用于评估给定喷发给当地社区带来的危险。此外，这项工作将为数值和实验研究提供喷发参数和物理方面的约束。最近火山喷流的次声记录具有与人造喷流(喷流噪声)产生的声波信号相似的频谱。在过去的60年里，空气声学一直在研究人造射流的流动特性与产生的声学信号之间的关系。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。这项工作是迈向这一长期目标的第一步。我们首先建立次声喷流噪声观测目录，以确定火山喷流噪声的特征特征，并确定这些特征与已知喷发参数之间的任何关联。这一过程包括使用新的信号处理工具以及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，将已建立的人造喷流噪声的经验模型应用于火山系统。该项目得到了地球物理和岩石学与地球化学计划和刺激竞争研究的实验计划(EPSCoR)的支持。

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).