Stratospheric Smoke With Unprecedentedly High Backscatter Observed by Lidars Above Southern France

Abstract

Extreme pyroconvection events triggered by wildfires in northwest Canada and United States during August 2017 resulted in vast injection of combustion products into the stratosphere. The plumes of stratospheric smoke were observed by lidars at Observatoire de Haute‐Provence (OHP) for many weeks that followed the fires as distinct aerosol layers with backscatter reaching unprecedentedly high values for a nonvolcanic aerosol layer. We use spaceborne CALIOP lidar to track the spatiotemporal evolution of the smoke plumes before their detection at OHP. A remarkable agreement between ground‐ and spaced‐based lidars sampling the same smoke plume on a particular date allowed us to extrapolate the OHP observations to a regional scale, where CALIOP reported extreme aerosol optical depth values as high as 0.21. On a monthly time scale, the lidar observations indicate that boreal summer 2017 forest fires had a hemisphere‐scale impact on stratospheric aerosol load, similar to that of moderate volcanic eruptions.

Extreme levels of Canadian wildfire smoke in the stratosphere over central Europe on 21–22 August 2017

“…According to the backward trajectories, the smoke traveled for about 7-10 days from western Canada to central Europe. This is in good agreement with the travel time derived from the spaceborne CALIPSO lidar observation presented by Khaykin et al (2018).…”

“…The apparently ascending stratospheric soot layer (observed from 21 to 23 August) is the results of two different influences. Khaykin et al (2018) found that the smoke plumes ascended rapidly over the first few days following their injection into the upper troposphere with a rate of 2-3 km per day. This cross isentropic ascent was caused by radiative heating of smoke aerosols (Boers et al, 2010).…”

“…We combined the analysis of forward trajectories with daily maps of OMI AI, MODIS 550 nm AOT, and the UV aerosol index (UVAI) obtained from observations with the spaceborne OPMS (Ozone Mapping and Profiler Suite) as presented in the Supporting Information S2 of Khaykin et al (2018). Our study was guided by the fact that a rather strong pyrocumulonimbus complex (generated from five thunderstorms) developed over the fire areas in southern-central British Columbia (see B.C.…”

“…Khaykin et al (2018) further pointed out that the optically dense smoke plumes obviously ascended by about 2-3 km per day during the first few days following their injection into the upper troposphere and lower stratosphere. The smoke layers were observed throughout Europe by the groundbased lidar systems of the European Aerosol Research Lidar Network (EARLINET) (Pappalardo et al, 2014) and further lidars operated in a long-term mode (Khaykin et al, 2018). Traces of stratospheric smoke were continuously detected over Europe until the end of 2017.…”

“…According to spaceborne CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) lidar observations presented by Khaykin et al (2018) the fire aerosol traveled eastward after entering the upper troposphere and lower stratosphere, crossed the North Atlantic, Europe, northern Asia, and circled around the globe within less than 20 days. Khaykin et al (2018) further pointed out that the optically dense smoke plumes obviously ascended by about 2-3 km per day during the first few days following their injection into the upper troposphere and lower stratosphere.…”