Simulating the Transport and Dispersal of Volcanic Ash Clouds With Initial Conditions Created by a 3D Plume Model

Marcus Bursik,Qingyuan Yang,Abani Patra,Zhixuan Cao

doi:10.3389/feart.2021.704797

Abstract

Volcanic ash transport and dispersion (VATD) models simulate atmospheric transport of ash from a volcanic source represented by parameterized concentration of ash with height. Most VATD models represent the volcanic plume source as a simple line with a parameterized ash emission rate as a function of height, constrained only by a total mass eruption rate (MER) for a given total rise height. However, the actual vertical ash distribution in volcanic plumes varies from case to case, having complex dependencies on eruption source parameters, such as grain size, speed at the vent, vent size, buoyancy flux, and atmospheric conditions. We present here for the first time the use of a three-dimensional (3D) plume model based on conservation laws to represent the ash cloud source without any prior assumption or simplification regarding plume geometry. By eliminating assumed behavior associated with a parameterized plume geometry, the predictive skill of VATD simulations is improved. We use our recently developed volcanic plume model based on a 3D smoothed-particle hydrodynamic Lagrangian method and couple the output to a standard Lagrangian VATD model. We apply the coupled model to the Pinatubo eruption in 1991 to illustrate the effectiveness of the approach. Our investigation reveals that initial particle distribution in the vertical direction, including within the umbrella cloud, has more impact on the long-range transport of ash clouds than does the horizontal distribution. Comparison with satellite data indicates that the 3D model-based distribution of ash particles through the depth of the volcanic umbrella cloud, which is much lower than the observed maximum plume height, produces improved long-range VATD simulations. We thus show that initial conditions have a significant impact on VATD, and it is possible to obtain a better estimate of initial conditions for VATD simulations with deterministic, 3D forward modeling of the volcanic plume. Such modeling may therefore provide a path to better forecasts lessening the need for user intervention, or attempts to observe details of an eruption that are beyond the resolution of any potential satellite or ground-based technique, or a posteriori creating a history of ash emission height via inversion.

Highlights

Volcanic ash, the fine-grained fraction of tephra, can be widely dispersed to synoptic and global scales and can lead to a degradation of air quality and pose threats to aviation (Tupper et al, 2007)
This study presents, for the first time, volcanic ash transport and dispersion (VATD) simulations using initial source conditions created by a 3D plume model
A case study of the 1991 Pinatubo eruption demonstrates that a 3D plume model can create more realistic initial ash cloud and ash parcel positions and improve the accuracy of ash transport forecasts

Summary

Introduction

The fine-grained fraction of tephra, can be widely dispersed to synoptic and global scales and can lead to a degradation of air quality and pose threats to aviation (Tupper et al, 2007). Numerous volcanic ash transport and dispersion (VATD) forecast models have been developed by both civil and military aviation, and meteorological agencies, to provide forecasts of ash cloud motion (Witham et al, 2007), such as Puff (Tanaka, 1991; Searcy et al, 1998), NAME (Jones et al, 2007), HYSPLIT (Stein et al, 2015; Rolph et al, 2017), and Ash3d (Schwaiger et al, 2012). New techniques have been integrated into VATDs to satisfy increasing demands for different types of output, model accuracy, and forecast reliability. This contribution explores a forward modeling method for creating initial conditions for VATD simulations, which promises to reduce the need for inversion or user intervention and improve forecasting

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