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Special Issue "Atmospheric Turbulence Processes and Wildland Fires"

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A special issue of Atmosphere (ISSN 2073-4433). This special issue belongs to the section "Biosphere/Hydrosphere/Land–Atmosphere Interactions".

Deadline for manuscript submissions: closed (10 November 2020) | Viewed by 8415

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Special Issue Editor

Dr. Warren E. Heilman

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Guest Editor

USDA Forest Service, Lansing, MI, USA
Interests: fire–fuel–atmosphere interactions; atmospheric turbulence; smoke dispersion; fire behavior; fire weather

Special Issue Information

Dear Colleagues,

Accurately predicting wildland fire behavior and the dispersion of smoke from wildland fires are two important issues that confront fire- and air-quality managers in their efforts to minimize the potential adverse impacts of wildland fires. Previous studies have shown that ambient and fire-induced atmospheric turbulent circulations can influence how fires spread across the landscape and how smoke from these fires is dispersed locally and regionally. However, much is still unknown about the properties of turbulence regimes in wildland fire environments, and this lack of understanding has limited our ability to develop new and improved fire behavior and smoke dispersion prediction systems that more accurately account for atmospheric turbulence processes.

The purpose of this Special Issue is to highlight recent research on atmospheric turbulence regimes and processes in wildland fire environments through theoretical investigations, field measurements, and/or numerical modeling. Manuscripts addressing any aspect of atmospheric turbulence as it relates to wildland fires are welcome, including but not limited to the following:

The effects of complex terrain and forest vegetation on fire-induced turbulence;
Turbulence effects on smoke-plume dynamics;
Correlations of fire behavior with the spatial and temporal variability of turbulence in the fire environment;
Recent advances in turbulence parameterizations for operational fire behavior and smoke dispersion systems;
Turbulent heat and momentum flux variability in the fire environment;
Case studies of past wildland fire events using coupled atmosphere/fire-behavior modeling systems;
Turbulence impacts on ember transport and deposition.

Dr. Warren E. Heilman
Guest Editor

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Keywords

Atmospheric turbulence
Wildland fires
Field measurements
Numerical modeling
Fire behavior
Smoke dispersion.

Published Papers (4 papers)

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Research

Open AccessArticle

Evolution of Plume Core Structures and Turbulence during a Wildland Fire Experiment

Maritza Arreola Amaya

and

Craig B. Clements

Atmosphere 2020, 11(8), 842; https://doi.org/10.3390/atmos11080842 - 09 Aug 2020

Cited by 5 | Viewed by 2015

Abstract

Micrometeorological observations were made during a prescribed fire experiment conducted in a region of complex terrain with grass fuels and weak ambient winds of 3 m s⁻¹. The experiment allowed for the analysis of plume and turbulence structures including individual plume core evolution during fire front passage. Observations were made using a suite of in situ and remote sensing instruments strategically placed at the base of a gully with a 24° slope angle. The fire did not spread upwards along the gully because the ambient wind was not in alignment with the slope, demonstrating that unexpected fire spread can occur under weak wind conditions. Our observational results show that plume overturning caused downward heat transport of −64 kW m⁻² to occur and that this mixing of warmer plume air downward to the surface may result in increased preheating of fine fuels. Plume evolution was associated with the formation of two plume cores, caused by vigorous entrainment and mixing into the plume. Furthermore, the turbulence kinetic energy observed within the plume was dominated by horizontal velocity variances, likely caused by increased fire-induced circulations into the plume core. These observations highlight the nature of plume core separation and evolution and provide context for understanding the plume dynamics of larger and more intense wildfires. Full article

(This article belongs to the Special Issue Atmospheric Turbulence Processes and Wildland Fires)

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Open AccessArticle

Identifying Characteristics of Wildfire Towers and Troughs

and

Atmosphere 2020, 11(8), 796; https://doi.org/10.3390/atmos11080796 - 28 Jul 2020

Cited by 3 | Viewed by 2152

Abstract

Wildfire behavior is dictated by the complex interaction of numerous physical phenomena including dynamic ambient and fire-induced winds, heat transfer, aerodynamic drag on the wind by the fuel and combustion. These phenomena create complex feedback effects between the fire and its surroundings. In this study, we aim to study the mechanisms by which buoyant flame dynamics along with vortical motions and instabilities control wildfire propagation. Specifically, this study employs a suite of simulations conducted with the physics-based coupled fire-atmosphere behavior model (FIRETEC). The simulations are initialized with a fire line and the fires are allowed to propagate on a grass bed, where the fuel heights and wind conditions are varied systematically. Flow variables are extracted to identify the characteristics of the alternating counter-rotational vortices, called towers and troughs, that drive convective heat transfer and fire spread. These vortices have previously been observed in wildfires and laboratory fires, and have also been observed to arise spontaneously in FIRETEC due to the fundamental physics incorporated in the model. However, these past observations have been qualitative in nature and no quantitative studies can be found in the literature which connected these coherent structures fundamental to fire behavior with the constitutive flow variables. To that end, a variety of state variables are examined in the context of these coherent structures under various wind profile and grass height conditions. Identification of various correlated signatures and fire-atmosphere feedbacks in simulations provides a hypothesis that can be tested in future observational or experimental efforts, potentially assisting experimental design, and can aid in the interpretation of data from in situ detectors. Full article

(This article belongs to the Special Issue Atmospheric Turbulence Processes and Wildland Fires)

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Open AccessArticle

Role of Horizontal Eddy Diffusivity within the Canopy on Fire Spread

Yana Bebieva

Julia Oliveto

Bryan Quaife

Nicholas S. Skowronski

Warren E. Heilman

and

Kevin Speer

Atmosphere 2020, 11(6), 672; https://doi.org/10.3390/atmos11060672 - 26 Jun 2020

Cited by 4 | Viewed by 2024

Abstract

Wind profile observations are used to estimate turbulent mixing in the atmospheric boundary layer from 1 m up to 300 m height in two locations of pine forests characteristic of the southeast US region, and to 30 m height at one location in the northeast. Basic turbulence characteristics of the boundary layers above and within the canopy were measured near prescribed fires for time periods spanning the burns. Together with theoretical models for the mean horizontal velocity and empirical relations between mean flow and variance, we derive the lateral diffusivity using Taylor’s frozen turbulence hypothesis in the thin surface-fuel layer. This parameter is used in a simple 1D model to predict the spread of surface fires in different wind conditions. Initial assessments of sensitivity of the fire spread rates to the lateral diffusivity are made. The lateral diffusivity with and without fire-induced wind is estimated and associated fire spread rates are explored. Our results support the conceptual framework that eddy dynamics in the fuel layer is set by larger eddies developed in the canopy layer aloft. The presence of fire modifies the wind, hence spread rate, depending on the fire intensity. Full article

(This article belongs to the Special Issue Atmospheric Turbulence Processes and Wildland Fires)

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Open AccessArticle

Fire Behavior, Fuel Consumption, and Turbulence and Energy Exchange during Prescribed Fires in Pitch Pine Forests

Kenneth L. Clark

Warren E. Heilman

Nicholas S. Skowronski

and

Atmosphere 2020, 11(3), 242; https://doi.org/10.3390/atmos11030242 - 29 Feb 2020

Cited by 11 | Viewed by 1868

Abstract

Prescribed fires are conducted extensively in pine-dominated forests throughout the Eastern USA to reduce the risk of wildfires and maintain fire-adapted ecosystems. We asked how fire behavior and fuel consumption during prescribed fires are associated with turbulence and energy fluxes, which affect the dispersion of smoke and transport of firebrands, potentially impacting local communities and transportation corridors. We estimated fuel consumption and measured above-canopy turbulence and energy fluxes using eddy covariance during eight prescribed fires ranging in behavior from low-intensity backing fires to high-intensity head fires in pine-dominated forests of the New Jersey Pinelands, USA. Consumption was greatest for fine litter, intermediate for understory vegetation, and least for 1 + 10 hour wood, and was significantly correlated with pre-burn loading for all fuel types. Crown torching and canopy fuel consumption occurred only during high-intensity fires. Above-canopy air temperature, vertical wind velocity, and turbulent kinetic energy (TKE) in buoyant plumes above fires were enhanced up to 20.0, 3.9 and 4.1 times, respectively, compared to values measured simultaneously on control towers in unburned areas. When all prescribed fires were considered together, differences between above-canopy measurements in burn and control areas (Δ values) for maximum Δ air temperatures were significantly correlated with maximum Δ vertical wind velocities at all (10 Hz to 1 minute) integration times, and with Δ TKE. Maximum 10 minute averaged sensible heat fluxes measured above canopy were lower during low-intensity backing fires than for high-intensity head fires, averaging 1.8 MJ m⁻² vs. 10.6 MJ m⁻², respectively. Summed Δ sensible heat values averaged 70 ± 17%, and 112 ± 42% of convective heat flux estimated from fuel consumption for low-intensity and high-intensity fires, respectively. Surprisingly, there were only weak relationships between the consumption of surface and understory fuels and Δ air temperature, Δ wind velocities, or Δ TKE values in buoyant plumes. Overall, low-intensity fires were effective at reducing fuels on the forest floor, but less effective at consuming understory vegetation and ladder fuels, while high-intensity head fires resulted in greater consumption of ladder and canopy fuels but were also associated with large increases in turbulence and heat flux above the canopy. Our research quantifies some of the tradeoffs involved between fire behavior and turbulent transfer of smoke and firebrands during effective fuel reduction treatments and can assist wildland fire managers when planning and conducting prescribed fires. Full article

(This article belongs to the Special Issue Atmospheric Turbulence Processes and Wildland Fires)

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