Crib fires are a way to produce fires with higher repeatability than generally is the case for wildland and urban scenarios and consequently are used to study fire behavior. Models for simulating large-scale fires benefit from characterization against relevant test conditions. Here we describe a modeling and experimental effort to better explore fire dynamics at the larger range of what is achievable in laboratories. The modeling that corresponds to the tests is used to provide parameters to larger-scale transport modeling efforts for climate effects as well as to evaluate modeling under oxygen vitiated conditions arising from partial enclosure conditions. Modeled pyrolysis rates and environmental conditions correspond reasonably well to the extinction regimes articulated in prior experimental work for under-ventilated fires expressed via the ventilation parameter for five ventilation conditions that vary across different response regimes. This suggests several potential aspects of model utility for large urban scenarios where structures restrict ventilation, and fires burn differently in response to the change in oxygen availability.

Megafires are increasingly generating Pyrocumulus clouds (PyroCus) through the interplay of atmospheric conditions such as stability and humidity, hot updrafts, and emitted aerosols from burning vegetation.

We present a statistical characterization of the interaction between a planar shock and a finite-diameter, cylindrical column of dense gas based on three-dimensional, large-eddy simulation results. In the simulation, the column of gas is initially inclined at an angle $\alpha _0$ with respect to the shock plane. Effects of the initial column angle on the mixing characteristics are examined at Mach number 2.0 for column incline angles $1^\circ$ , $5^\circ$ , $10^\circ$ and $30^\circ$ . Mean velocity profiles show that the column angle affects the gas velocity components in the vertical plane, but not in the spanwise direction. The gas undergoes higher initial upward acceleration at larger initial column incline angles. With time, the gas motion tends to become one-dimensional in the streamwise direction. Initially, velocity fluctuations are most intense within the interior of the column, but concentrate near the column leading edge over time. At high wavenumbers $\kappa$ , the turbulent kinetic energy spectra follow a power-law scaling of $\kappa ^{-1}$ . The structure functions of the mass fraction do not clearly demonstrate power-law scaling except at early times for $\alpha _0=30^\circ$ , manifesting overall trends very similar to those observed in earlier experiments. Probability distributions of the mass fraction show independence of the mean and the standard deviation of the mixed gas on $\alpha _0$ . The column angle was also found to have little effect on the mixing efficiency characterized by the molecular mixedness. Velocity components in the streamwise and transverse directions tend towards a bimodal distribution for larger $\alpha _{0}$ .

Pyrocumulonimbus (PyroCb) clouds have a complex origin dependent on fire dynamics and meteorological conditions. When a pyrocumulonimbus cloud develops and is maintained over a period of time, it can inject significant aerosol into the troposphere and lower stratosphere, resulting in a longer-term (months to years) occurrence of aerosol in the stratosphere. In this work, we investigate the British Columbia wildfires on 12-13 August 2017 using a multi-scale simulation framework. We use the output of a physics-based wildfire model (FIRETEC) with parameterized energy, particle, and gas emissions to drive the upper atmospheric aerosol mass injection within a regional cloud resolving model (HIGRAD). We demonstrate that vertical motions produced by latent heat release of the condensation of ice and cloud particles within the PyroCbs induce another 5 km of lifting of the simulated aerosol plume. Primary black carbon and organic aerosols (OAs) alone may not be enough to explain the observed aerosol burden, thus we show that secondary OA produced via condensation of gases by the fires, ash, and possibly dust can enhance lofted aerosol mass. A simulation with all emission mechanisms active, driven by the observed fuel load and environmental conditions, reasonably reproduces an aerosol profile inferred from observational data.

Although fires are the primary source for black carbon (BC) from a regional nuclear exchange, climate simulations have traditionally approximated the source term for scenario estimates. While approaches and suggested parameters were outlined by the U.S. National Academies of Science study in 1985, there has not been an update to these recommendations. The emissions from fires induced by the detonation of a nuclear weapon in an urban environment involve significant complexities, and this manuscript provides a survey of updated parameters for climate estimates and a critical evaluation of their validity in the context of the large-scale fires anticipated from such an event. The purpose of this work is to help progress the methodologies for estimating BC sources and stratospheric injection and to guide the application of uncertainties and more advanced modeling towards improved fire consequence estimates in support of the hazard assessments.

In this paper, we present three-dimensional simulation results of the interaction between a planar shock and a finite-diameter, cylindrical column of dense gas. This column of gas is initially inclined at an angle 𝛼0 with respect to the shock. After passage of the shock, a counter-rotating vortex pair is observed in the cross-sectional plane through the column midpoint. In addition, a shear driven instability, known as the shock-driven Kelvin-Helmholtz instability(SDKHI) develops on the column surface. In this study, we investigate the three-dimensional effects of the SDKHI with a focus on two parameters; the initial column angle (𝛼0 = 10°, 20°, 30°) and the Mach number (𝑀1 = 1.4, 1.7, 2.0). Comparison is also made to results from previous two-dimensional studies on the interaction of a shock with an inclined, finite width curtain. Simulations were performed with FIESTA, a GPU accelerated compressible flow solver developed at the University of New Mexico.

Stratospheric injections of carbonaceous aerosols and combustion gases by extreme wildfires have become increasingly common. Recent “megafires,” particularly large and intense fires, delivered particulate burdens to the lower stratosphere comparable to those of moderate volcanic eruptions. The 2017 Canadian megafire generated four large Pyrocumulonimbi (pyroCbs), injecting up to ≈0.3 Tg of smoke in the lower stratosphere. Even more extreme, the 2019/2020 Australian event produced a pyroCb activity resulting in stratospheric smoke intrusions of ≈1 Tg. To understand their contrasting behavior, we present global climate simulations of the atmospheric response to these events, applying smoke burdens informed by remote observations. Model outcomes, compared to satellite data of smoke transport, reproduce reasonably well the initial plume rise, at 0.2–0.3 km/day, attaining heights of ≈20 km in Canada and above 30 km in Australia. Global dispersal of the plume occurs within about 3 weeks in both cases, consistent with observations. Smoke removal timescales, ≈5 months for the Canadian megafire, agree with remote measurements. During the Australian megafire, observations indicate stratospheric injections three times as large, and models predict comparatively longer smoke lifetimes, ≈16 months. After the latter event, atmospheric optical depths and radiative cooling achieved values close to those measured following the Pinatubo eruption. Sensitivity tests of model assumptions indicate, in accord with prior studies, that smoke burden, injection heights, and black carbon content can determine plume evolution and possible climate impacts. An empirical relation between peak heights of stratospheric plumes and lifetimes is derived that can help assess megafire impacts on the stratosphere, climate and the Earth system.

In this paper, we present simulation results for the three-dimensional, shock-driven Kelvin-Helmholtz instability.Simulations are performed with a Mach 2.0 shock propagating through a finite-diameter cylindrical column of dense gas inclined at an angle θ with respect to the shock plane.After passage of the shock, the gas curtain has accelerated along its axis and a Kelvin-Helmholtz instability forms on the column surface.This is the first known numerical reproduction of this phenomena in three dimensions, which has previously been observed in experiments with an inclined cylindrical gas column.The effects of changes to initial column angle (θ = 0 • , 10 • , 20 • , 30 • ) are explored in detail to complement experimental data.The effects of shock reflection near the base of the column are also examined to identify a possible flow perturbation near the foot which was seen in our previous two-dimensional numerical studies of shock-accelerated inclined gas curtains.The overall flow morphology compares well with experimental data in a cross-sectional plane through the column midpoint and a vertical plane through the column axis.Simulations were performed with FIESTA, an exascale ready, GPU accelerated compressible flow solver developed at the University of New Mexico.

Airborne measurements of upper troposphere and lower stratosphere biomass burning smoke show a large size mode at 350nm radius. Furthermore, very thickly coated black carbon (300-400nm radius) is observed in 2 month aged Pyro-cumulonimbus (PyroCb) smoke in the lower stratosphere. Finally, the stratospheric aerosol mass injections from the 2017 British Columbia (BC17) PyroCbs are much larger than fuel loading predicts. We propose a secondary organic aerosol (SOA) production mechanism where volatile organic compounds (VOCs) emitted by fires condense in the cold convective PyroCb updrafts to explain the aforementioned data. Observations supporting this mechanism present in FIREX-AQ, ATOM and CARIBEC airborne data are synthesized. The condensation, evaporation and coagulation mechanisms are implemented into LANL’s large eddy cloud resolving model called HIGRAD. Our simulations provide insights into the vertical distribution of SOA in the BC17 PyroCb and the role of warm and ice clouds in lofting it into the lower stratosphere. We show that SOA formation can increase aerosols by a factor of 2-3 and latent heat from warm and ice clouds adds 5 km to the injection height of BC17 fire smoke. The fate, transport and impacts of smoke from BC17 and 2020 Australian fires are examined using climate model (CESM) simulations.

How many should we have. Why have any. This essay does not seek to provide a comprehensive review of nuclear strategy since 1945, nor does it provide detailed recommendations for future strategy. Rather, it introduces a new paradigm, a new structure, a new set of lenses, which permits the strategist to seek old familiar information in a different context. Taking strategy to include ends, ways, and means, the new paradigm introduced herein interprets the past 45 years as three discernible time periods, each with a different characteristic.

In this paper, we present simulation results for the two-dimensional, shock-driven Kelvin–Helmholtz instability. Simulations are performed with a Mach 2.0 shock propagating through a finite-thickness curtain of gas inclined at an angle α 0 = 30 ° with respect to the shock plane. After the passage of the shock, the gas curtain is accelerated along its axis. A perturbation develops due to shock reflection near the lower wall, and a Kelvin–Helmholtz instability forms near the vertical center of the curtain. This is the first known numerical reproduction of these phenomena that have previously been observed in experiments with an inclined cylindrical gas column. The effects of varying Mach number and column width were explored in detail to complement experimental data. The dependence of the Kelvin–Helmholtz wavelength on Mach number closely matches the relationship observed in experiments. This supports the notion that the observed instability is effectively two-dimensional and inviscid (like classical Kelvin–Helmholtz). The growth rate of the perturbations in the gas curtain was also found to be similar for different Mach numbers. The perturbation at the curtain foot, previously unreported in experiments, was found to have a similar relationship to Mach number as the Kelvin–Helmholtz instability. Both perturbation wavelengths are found to be proportional to layer width. Simulations were performed with the fast interfaces and transport in the atmosphere, an exascale ready, graphics processing unit-accelerated compressible flow solver developed at the University of New Mexico.

Particle and trace gas emissions can undergo rapid changes in the atmosphere as a result of evaporation, condensation, and coagulation processes that are driven by dynamics and photochemistry. Here we analyze the fate of non-methane hydrocarbons (NMHCs) gases emitted by intense fires associated with pyroCbs towers that rise and cool rapidly and undergo relatively little dilution as they loft smoke into the upper troposphere and lower stratosphere. We use airborne observations of plumes from the Williams Flats Fire over the continental United States taken during 2019 FIREX-AQ campaign. Trace gas data from both fresh boundary smoke and PyroCb-lofted smoke from this fire are compared to that from smoke plumes that stayed at lower altitudes to constrain the roles of condensation, cloud processing and photochemistry in the outflow of pyroCbs. In the pyroCb outflows we observe lower CO normalized NMHCs mixing ratios with low vapor pressure compared to the boundary layer samples while for high vapor pressure compounds there is little difference between the CO normalized NMHC mixing ratios observed in the different fresh smoke plumes. Associated with this decrease in condensable NMHCs we find an increase in particle concentrations, specifically at large sizes (~350nm). These multiple observational facts are used to estimate the secondary organic aerosol production by NMHC condensation in pyroCb. Further analysis of FIREX-AQ data will be used to elucidate the roles of solubility and photochemistry on SOA formation in pyroCbs. These FIREX-AQ results will be used to inform cloud resolving large eddy simulation (LES, HIGRAD) to examine deep convective fire impacts on long range smoke impacts on climate and air quality.

In this work, the experimentally observed shock driven Kelvin-Helmholtz instability is reproduced numerically. Results for two sets of two-dimensional simulations are presented. The first of these simulations represents the interaction of a Mach 2.0 shock with a circular cloud of dense gas and is compared with experimental results. The second set of simulations are the interaction of a Mach 2.0 shock with a column of gas inclined at an angle $\alpha_0$ with respect to the shock. The second set of simulations shows the onset of a Kelvin-Helmholtz instability proceeding the passage of the shock through the column of dense gas. Both concentration and vorticity fields are visualized to confirm that the phenomenon is indeed a Kelvin-Helmholtz instability. The dependence of Kelvin-Helmholtz wavelength on the initial column angle was investigated and found to be weak. A second instability was identified at the bottom of the gas column which has not been previously investigated in detail. This instability also does not have a strong dependence on the initial column angle.