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Level 2 OMPS AAI, August 12, 2017. The color scale varies from light to dark brown with increasing AAI, the scene maximum of which is annotated at top left. An asterisk marks the location of maximum AAI. Forward trajectories from the locations of two August 11 pyroCbs (filled square and triangle) at 02:00 and 05:00 UTC August 12, respectively, and terminating at 20:00 UTC August 12 (black lines). The trajectories were initialized at 11 km asl.
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Wildfire‐generated thunderstorms, which in ways resemble explosive volcanic eruptions, can dot the landscape as an individual blowup or a cluster over a complex of fires. A technical term for these storm clouds is “pyrocumulonimbus” (“pyroCb” for short). The Pacific Northwest Event (PNE) pyroCbs in 2017 gained wide attention....
Citations
... For instance, Peterson et al. (2018) showed that in August 2017 the mass of smoke aerosol particles injected into the lower stratosphere from five near-simultaneous pyroCb was comparable to a moderate volcanic eruption. Fromm et al. (2021) studied the same time period and revealed at least two pyroCb clouds injecting smoke above 13.5 km up to 2.5 km above the local tropopause. Over Canada, the extreme pyroCb activity recorded in August 2017 also resulted in a high-arctic smoke event (Ranjbar et al., 2019). ...
... de Laat et al. (2012) examined observations from multiple datasets, including Ozone Monitoring Instrument (OMI) and Global Ozone Monitoring Experiment (GOME-2) aerosol index, Atmospheric Infrared Sounder (AIRS) CO, and aerosol observations from Moderate Imaging Spectroradiometer (MODIS) and CALIOP. Further analysis by Fromm et al. (2021) of the Black Saturday plume included OMI aerosol index, MODIS imagery, MLS CO, and CALIOP. Glatthor et al. (2013) examined Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) C 2 H 2 , HCN, and HCOOH measurements of the plume, comparing with simulations from the Global Environmental Multiscale Air Quality (GEM-AQ) model. ...
... A region of enhanced CO was observed in this region on 12-13 February, as shown in Figure 1 of Pumphrey et al. (2011). We note that Fromm et al. (2021) quoted a "day after" height of ∼16-17 km, (θ ∼ 374-386 K) for the Black Saturday SWIRL, so this feature likely rose diabatically prior to our discernment of an isolated SWIRL on 13 February at 18.4 km (θ c = 412 K). While the PV anomaly shown here for the SH is positively signed, SWIRLs (in both hemispheres) are characterized by lower absolute PV. ...
The discovery of smoke‐induced dynamical anomalies in the stratosphere associated with the 2019/2020 Australian New Year pyrocumulonimbus (pyroCb) super outbreak initiated a new field of study involving aerosol/weather anomalies. This paper documents the dynamical anomalies associated with the February 2009 Australian Black Saturday pyroCb outbreak. Positive potential vorticity anomalies (indicating anticyclonic rotation) with horizontal extent ∼1000 km and vertical thickness ∼2 km are associated with the plume, which we classify as a Smoke With Induced Rotation and Lofting (SWIRL). The SWIRL initially formed east of Australia, but then moved westward, crossing over Australia, and continuing to Africa. The SWIRL lasted for nearly three weeks (13 February–4 March), traveling ∼27,000 km and rising from potential temperatures of ∼410–500 K (altitudes ∼18–21 km). The altitude of the SWIRL is corroborated with coincident satellite‐based profiles of H2O, CO, HCN, O3, and aerosol extinction. A vertical temperature dipole (±3 K) accompanied the PV anomaly, as verified with coincident Global Navigation Satellite System radio occultation temperatures. The SWIRL dissipated as it passed over Africa. Operational ECMWF forecasts with early initialization (13 February) and late initialization (21 February) are examined. In the early case, the forecasted PV anomaly disappeared within 4 days, as expected due to lack of smoke heating in the forecast model. In the late case, while the forecasted PV anomaly was weaker than in the reanalyzes, a remnant anomaly remained out to 10 days.
... The most spectacular event was that of the wild fires in British Columbia starting in August 2017. Peterson et al. (2018) and Fromm et al. (2021) report that the mass of smoke aerosol particles injected into 55 the lower stratosphere from five near-simultaneous intense pyro-cumulonimbus (pyroCb) events occurring in western North America on 12 August 2017 was comparable to that of a moderate volcanic eruption, and one order of magnitude larger than previous benchmarks for extreme pyroCb activity. ...
... The first, particularly spectacular signature after resuming the measurements at UFS in 2017 was identified as 265 the result of the pyroCbs in British Columbia (B.C.) on 11 and 12 August 2017 that acted like a volcanic eruption (Peterson et al., 2018;Fromm et al., 2021). In general, the B.C. fire season during that year lasted several months, starting on 6 July. ...
... The first burst of pyroCbs was reported by Fromm et al. (2021) for 12 August, at about 23:00 UTC, the last one at about 6:45 UTC on the following day. Several times altitudes between 13 km and 13.7 km were recorded by the Prince George radar. ...
The highlight of the meanwhile 50 years of lidar-based aerosol profiling at Garmisch-Partenkirchen has been the measurements of stratospheric aerosol since 1976. After a technical breakdown in 2016, they have been continued with a new, much more powerful system in a vertical range up to almost 50 km a.s.l. that allowed to observe very weak volcanic aerosol up to almost 40 km. The observations since 2017 are characterized by a number of spectacular events, such as the Raikoke volcanic plume equalling in integrated backscatter coefficient that of Mt. St. Helens in 1981 and severe smoke from several big fires in North America and Siberia with backscatter coefficients up to the maximum values after the Pinatubo eruption. The smoke from the violent 2017 fires in British Columbia gradually reached more than 20 km a.s.l., unprecedented in our observations. The sudden increase in frequency of such strong events is difficult to understand. Finally, the plume of the spectacular underwater eruption on the Tonga islands in the southern Pacific in January 2022 was detected between 20 and 25 km.
... However, in the case of wildfires such as the 2017 BCE fires where strong pyroCb events occurred, this injection scheme may not properly reflect reality as pyroCb smoke plumes can rise to extreme altitudes before they are transported laterally. Fromm et al. (2021) and Peterson et al. (2018) termed the BC pyroCb event the Pacific Northwest Event (PNE), and demonstrated that the smoke from these fires was injected directly into the lower stratosphere at an altitude of approximately 12-13 km before being lofted northwards, which represents a significant disparity with the values provided by GFAS. ...
... This model error was determined to be a direct result of the method through which the biomass burning emissions are injected into the vertical model grid. The injection height of the BC fires has been examined in detail in the literature (e.g., Bourassa et al., 2019;Fromm et al., 2021;Peterson et al., 2018;Torres et al., 2020), and it is generally understood that the plume was injected into the UTLS with a mean altitude of 12-13 km above the fires, with the top of the injected plume reaching as high as 13.7 km. However, the injection and plume height of the NWT fires has not been examined in the same depth, and is not well constrained. ...
... To ascertain an appropriate injection height for the NWT fires, we performed a series of simulations with variable injection heights for the NWT fires, while using a fixed injection height of 12.5 km for the BC fires based on Fromm et al. (2021) and Peterson et al. (2018), and we used both CO and PAN as tracers for the plume transport. CO was chosen because its long atmospheric lifetime means that it will be minimally affected by chemical aging over the course of a few days, and PAN was selected as a secondary tracer since it is highly sensitive to the transport altitude as a result of the strong temperature dependence of its atmospheric lifetime. ...
Extreme enhancements in the total columns of carbon monoxide (CO), peroxyacetyl nitrate (PAN), ethylene (C2H4), methanol (CH3OH), and formic acid (HCOOH) were observed over the Canadian high Arctic during the period of 17–22 August 2017 by a ground‐based Fourier transform infrared (FTIR) spectrometer at Eureka, Nunavut (80.05°N, 86.42°W), and by the Infrared Atmospheric Sounding Interferometer (IASI) satellite instruments. These enhancements have been attributed to wildfires in British Columbia (BC) and the Northwest Territories (NWT) of Canada, and represent the largest short‐term perturbations of PAN, C2H4, and HCOOH above ambient concentrations over the 14‐year (2006–2020) Eureka time‐series. Enhancement ratios, emission ratios, and emission factors relative to CO were calculated for all species for both FTIR and IASI observations. The C2H4 and HCOOH emission factors are significantly larger than previous studies, suggesting unusually high emissions from these fires. The wildfire plumes were also simulated using the GEOS‐Chem model. Initial GEOS‐Chem simulations displayed a severe under‐estimation relative to observations for these fire plumes resulting from the injection height scheme of the model. Sensitivity tests highlighted that injection heights of 12.5 km for BC (based on previous studies) and 10 km for the NWT fires yielded the strongest correlations with ground‐based measurements. Applying these injection heights to the model significantly improves the simulated plume transport and agreement with ground‐ and space‐based observations. GEOS‐Chem was also used to estimate the magnitude of secondary in‐plume production of CH3OH and HCOOH; it was found to be an important component (∼18%) of the enhanced HCOOH columns at Eureka.
... The Black Summer pyroCb super outbreak spawned a stratospheric smoke pall that garnered great attention worldwide. Smoke that was directly injected into the lowermost stratosphere, like many previous pyroCb plumes 13,29 , persisted for more than a year 7 and exhibited extraordinary features. The smoke rose into the middle stratosphere, far higher than any previous smoke had been observed 23 . ...
... These smoke enclosures were termed "smoke with induced rotation and lofting" (SWIRL) 31 . Curiosity is therefore increasing about this seemingly new coupling between pyroCb activity and diabatic plume lofting that is really not new at all 29 . ...
... The discovery of these pre-Black Summer SWIRLs was afforded by the new knowledge gained in the Black Summer smoke plume research. It is currently unclear how often these diabatically rising plume sub-elements have occurred historically 29 . Given that diabatic lofting of solar-heated stratospheric smoke plumes was central to the mechanism hypothesized in the Nuclear Winter 21 scenario, the observed manifestation of rapid stratospheric plume rise embodied by the SWIRL may represent a preferred or particularly efficient real-world pathway for modelers of Nuclear Winter scenarios to simulate. ...
High-intensity wildland fires can produce extreme flaming and smoke emissions that develop into a fire-cloud chimney, reaching into the upper troposphere or lower stratosphere. Termed pyrocumulonimbus, these storms are both conventional and counterintuitive. They have been observed to produce lightning, hail, downdraft wind hazards, and tornadoes as expected with severe convective storms, but counterintuitively, they are not associated with significant precipitation. Pyrocumulonimbus storms have been noticed outside wildfire expert circles following Australia’s Black Summer in 2019/20, and have since repeatedly made headlines in the United States. However, much is unknown about their behavior, energetics, history, and impact on the Earth/atmosphere system. We address several questions and science challenges related to these unknowns. Our worldwide record of pyrocumulonimbus events from 2013 to 2021 shows that the phenomenon is neither new nor rare. Despite high occurrences in 2019 and 2021, these data do not support identification of a trend. Future studies require an expansive record of pyrocumulonimbus occurrence globally and regionally, both historically and continuously forward in time.
... PyroCb clouds during a 2017 forest fire in southern British Columbia injected, or delivered by lofting, an estimated 33-300 thousand metric tons (0.033-0.300 Tg) of smoke particles into the lower stratosphere (Yu et al., 2019;Fromm et al., 2021) where their presence was apparent for ~10 months as the smoke traveled around Earth (Torres et al., 2020). The enormous New Year fires in southeastern Australia (2019-2020) burned ~74,000 km 2 and produced 38 pyroCb events, leading to injection and self-lofting of 400-900 thousand tons (0.4-0.9 Tg) of smoke into the stratosphere (Khaykin et al., 2020;Peterson et al., 2021;Yu et al., 2021). ...
The highlight of the meanwhile 50 years of lidar-based aerosol profiling at Garmisch-Partenkirchen has been the measurements of stratospheric aerosol since 1976. After a technical breakdown in 2016, they have been continued with a new, much more powerful system in a vertical range up to almost 50 km a.s.l. (above sea level) that allowed for observing very weak volcanic aerosol up to almost 40 km. The observations since 2017 are characterized by a number of spectacular events, such as the Raikoke volcanic plume equalling in integrated backscatter coefficient that of Mt St Helens in 1981 and severe smoke from several big fires in North America and Siberia with backscatter coefficients up to the maximum values after the Pinatubo eruption. The smoke from the violent 2017 fires in British Columbia gradually reached more than 20 km a.s.l., unprecedented in our observations. The sudden increase in frequency of such strong events is difficult to understand. Finally, the plume of the spectacular underwater eruption on the Tonga Islands in the southern Pacific in January 2022 was detected between 20 and 25 km.
As the climate system warms, megafires have become more frequent with devastating effects. A byproduct of these events is the creation of smoke plumes that can rise into the stratosphere and spread across the globe where they reside for many months. To gain a deeper understanding of the plume dynamics, global climate simulations of a megafire were performed at a wide range of grid spacings from 2.0° down to 7 km, including a 7 km nonhydrostatic experiment. The analysis focuses on how the resolved dynamics affects the specification of the plume characteristics such as injection height and black carbon (BC) mass. Prior studies initialize the smoke plume at one or a few grid points and this is shown here to produce severely dissipative dynamics. In order to validate such simulations with observations, enhancements of the plume characteristics to offset the dissipation is necessary. Using a numerically converged simulation, sensitivity tests show that to approximate the observed stratospheric lifetime, a reduction in BC fraction by 50% is necessary for external mixtures. The vorticity dynamics of the plume is also analyzed with a Lagrangian budget to understand the mechanisms responsible for the evolution of a collocated anticyclonic vortex. The results can be distilled down into a simple conceptual model. As the plume rises, the air diverges at the top of the updraft where the largest concentrations of smoke are found. This divergence induces a dilution of the background cyclonic absolute vorticity producing an anticyclonic vortex. Vortex decay occurs from opposite arguments.
The Pacific Northwest Pyrocumulonimbus Event (PNE) took place in British Columbia during the evening and nighttime hours between 12 and 13 August 2017. Several pyroconvective clouds erupted on this occasion, and released in the upper troposphere and lower stratosphere unprecedented amounts of carbonaceous aerosols (300 ktn). Only a few years later, an even larger pyrocumulonimbus (pyroCb) injection took place over Australia. This event, named “the Australian New Year (ANY) event”, injected up to 1100 ktn of aerosol between 29 December 2019 and 4 January 2020. Such large injections of carbonaceous aerosol modify the stratospheric radiative budgets, locally perturbing stratospheric temperatures and winds. In this study, we use the Goddard Earth Observing System Chemistry Climate Model (GEOS CCM) to study the perturbations on the stratospheric meteorology induced by an aerosol injection of the magnitude of the PNE. Our simulations include the radiative interactions of aerosols, so that their impact on temperatures and winds are explicitly simulated. We show how the presence of the carbonaceous aerosols from the pyroCb causes the formation and maintenance of a synoptic-scale stratospheric anticyclone. We follow this disturbance considering the potential vorticity anomaly and the brown carbon aerosol loading and we describe its dynamical and thermodynamical structure and its evolution in time. The analysis presented here shows that the simulated anticyclone undergoes daily expansion–compression cycles governed by the radiative heating, which are directly related to the vertical motion of the plume, and that the aerosol radiative heating is essential in maintaining the anticyclone itself.
