Pyro‐cumulonimbus injection of smoke to the stratosphere: Observations and impact of a super blowup in northwestern Canada on 3–4 August 1998

Abstract

We report observations and analysis of a pyro‐cumulonimbus event in the midst of a boreal forest fire blowup in Northwest Territories Canada, near Norman Wells, on 3–4 August 1998. We find that this blowup caused a five‐fold increase in lower stratospheric aerosol burden, as well as multiple reports of anomalous enhancements of tropospheric gases and aerosols across Europe 1 week later. Our observations come from solar occultation satellites (POAM III and SAGE II), nadir imagers (GOES, AVHRR, SeaWiFS, DMSP), TOMS, lidar, and backscattersonde. First, we provide a detailed analysis of the 3 August eruption of extreme pyro‐convection. This includes identifying the specific pyro‐cumulonimbus cells that caused the lower stratospheric aerosol injection, and a meteorological analysis. Next, we characterize the altitude, composition, and opacity of the post‐convection smoke plume on 4–7 August. Finally, the stratospheric impact of this injection is analyzed. Satellite images reveal two noteworthy pyro‐cumulonimbus phenomena: (1) an active‐convection cloud top containing enough smoke to visibly alter the reflectivity of the cloud anvil in the Upper Troposphere Lower Stratosphere (UTLS) and (2) a smoke plume, that endured for at least 2 hours, atop an anvil. The smoke pall deposited by the Norman Wells pyro‐convection was a very large, optically dense, UTLS‐level plume on 4 August that exhibited a mesoscale cyclonic circulation. An analysis of plume color/texture from SeaWiFS data, aerosol index, and brightness temperature establishes the extreme altitude and “pure” smoke composition of this unique plume. We show what we believe to be a first‐ever measurement of strongly enhanced ozone in the lower stratosphere mingled with smoke layers. We conclude that two to four extreme pyro‐thunderstorms near Norman Wells created a smoke injection of hemispheric scope that substantially increased stratospheric optical depth, transported aerosols 7 km above the tropopause (above ∼430 K potential temperature), and also perturbed lower stratospheric ozone.

A review of approaches to estimate wildfire plume injection height within large-scale atmospheric chemical transport models

“…The question of the impact of fire emission injection in the atmosphere was first introduced by Chatfield and Delany (1990) and was later extensively reported in EO data. For example, injections of gases and aerosols emitted from vegetation fires have been observed at various heights in troposphere and occasionally even the lower stratosphere (Fromm et al, 2005). Smoke remnants from certain tropical fires have been observed at 15 km altitude (Andreae et al, 2004), and plumes from individual Canadian stand-replacing forest fires can also reportedly approach such heights (Damoah et al, 2006).…”

Properties and evolution of biomass burning organic aerosol from Canadian boreal forest fires

“…Weaker convection resulting from smouldering fires limits vertical transportation, retaining plumes within the boundary layer (Andreae et al, 1996;Warneke et al, 2006;Burling et al, 2011). The presence of flaming-derived emissions at higher altitudes alludes to an elevated injection height resulting from increased buoyancy and pyroconvection (Fromm et al, 2005;Damoah et al, 2006) driven by more intense fires earlier in the BORTAS campaign period (Fig. 2).…”

Large sulfur-isotope anomaly in nonvolcanic sulfate aerosol and its implications for the Archean atmosphere

“…1B), and special processes are required for these two time periods. Assuming COS and SO 2 from wildfires as the source of sulfur in this period with higher altitude transport to the stratosphere (18,19) via pyrocumulus nimbus clouds (27), subsequent photochemistry of COS produced SO 2 above 25 km could provide an extra S-isotope anomaly source. The altitude for both SO 2 photo excitation and photolysis in this case likely differs from volcanic SO 2 due to its production above the ozone layer.…”