Impact of Extreme Wildfires on Stratospheric Composition from Satellite and Ground-based Observations
Résumé
The severity of wildfires has remarkably increased over the last years in both hemispheres and there is an emerging realization of their effect on climate and ozone layer. Intense wildfires can generate extreme thunderstorms termed Pyrocumulonimbus (PyroCb), that are capable of injecting smoke and other combustion products directly into the stratosphere, where the residence time of aerosols is not limited by cloud scavenging and precipitation. A number of recent studies have put in evidence that the effects of strong PyroCb events on the global stratosphere rival those of moderate volcanic eruptions in terms of magnitude and duration whilst exceeding them in terms of radiative forcing. Here we use global observations by MLS, OMPS, CALIPSO, SAGE III and TROPOMI satellite missions together with ground-based lidar records in France and New Zealand to characterize and quantify the planetary-scale impact of wildfire PyroCb on stratospheric gaseous composition and aerosol optical properties as follows. First, we identify the wildfire events during the last two decades with a measurable stratospheric impact and classify them into four categories ranging from 1 to 4 based on the magnitude and longevity of their stratospheric impact. Then, we quantify the aerosol and gas mass fluxes into the stratosphere for each event. Using a combination of nadir and limb observations along with ERA5 analysis, we explore the spatiotemporal evolution and dynamics of the stratospheric smoke plumes. We show evidence for the geographical and seasonal extension of the tropopause-overshooting PyroCb events. By using long- term ground-based and satellite lidar observations of depolarization, we point out the longevity of fine smoke particles in the stratosphere. Finally, we discuss the impact of the anomalous 2023 Canadian wildfires, which are shown to be responsible for a record-high and persistent season-wide smoke pollution at the commercial aircraft cruising altitudes and the lowermost stratosphere.