Wildfire smoke-plume rise: a simple energy balance parameterization

Nadya Moisseeva,Roland Stull

doi:10.5194/acp-21-1407-2021

Nadya Moisseeva, Roland Stull

Open Access

https://doi.org/10.5194/acp-21-1407-2021

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Abstract

Abstract. The buoyant rise and the resultant vertical distribution of wildfire smoke in the atmosphere have a strong influence on downwind pollutant concentrations at the surface. The amount of smoke injected vs. height is a key input into chemical transport models and smoke modelling frameworks. Due to scarcity of model evaluation data as well as the inherent complexity of wildfire plume dynamics, smoke injection height predictions have large uncertainties. In this work we use the coupled fire–atmosphere model WRF-SFIRE configured in large-eddy simulation (LES) mode to develop a synthetic plume dataset. Using this numerical data, we demonstrate that crosswind integrated smoke injection height for a fire of arbitrary shape and intensity can be modelled with a simple energy balance. We introduce two forms of updraft velocity scales that exhibit a linear dimensionless relationship with the plume vertical penetration distance through daytime convective boundary layers. Lastly, we use LES and prescribed burn data to constrain and evaluate the model. Our results suggest that the proposed simple parameterization of mean plume rise as a function of vertical velocity scale offers reasonable accuracy (30 m errors) at little computational cost.

Highlights

Predictions of surface concentrations of wildfire smoke by regional and global chemical transport models depend on the initial equilibrium height of the smoke plume
Through analysis of the 140 large-eddy simulation (LES) experiments for plumes under variable fire and atmospheric conditions, we found that near-surface and boundary-layer plume dynamics are extraordinarily complex
In this study we present a simple parameterization (Eq 8) for predicting CWI smoke-plume centerline height from a wildfire of an arbitrary shape and intensity

Summary

Introduction

Predictions of surface concentrations of wildfire smoke by regional and global chemical transport models depend on the initial equilibrium height of the smoke plume. In a recent review of existing plume rise parameterizations, Paugam et al (2016) highlight three notable models that stand out in the literature: those by Freitas et al (2007), Sofiev et al (2012) and Rio et al (2010) Both Freitas’ and Rio’s approaches use first principles to characterize plume temperature, vertical velocity and entrainment. While the approach by Freitas et al (2007) provides prognostic 1-D equations that can be solved as a stand-alone “offline” model, the approach by Rio et al (2010) is implemented as a sub-grid effect within a host chemistry transport model Both consider an idealized heat source to represent the fire. It is unclear whether unreliable predictions should be attributed to the fire input parameters or the plume rise model itself

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