Transport of the 2017 Canadian wildfire plume to the tropics via the Asian monsoon circulation

Abstract

Abstract. We show that a fire plume injected into the lower stratosphere at high northern latitudes during the Canadian wildfire event in August 2017 partly reached the tropics. The transport to the tropics was mediated by the anticyclonic flow of the Asian monsoon circulation. The fire plume reached the Asian monsoon area in late August/early September, when the Asian monsoon anticyclone (AMA) was still in place. While there is no evidence of mixing into the center of the AMA, we show that a substantial part of the fire plume is entrained into the anticyclonic flow at the AMA edge and is transported from the extratropics to the tropics, and possibly the Southern Hemisphere particularly following the north–south flow on the eastern side of the AMA. In the tropics the fire plume is lifted by ∼5 km in 7 months. Inside the AMA we find evidence of the Asian tropopause aerosol layer (ATAL) in August, doubling background aerosol conditions with a calculated top of the atmosphere shortwave radiative forcing of −0.05 W m−2. The regional climate impact of the fire signal in the wider Asian monsoon area in September exceeds the impact of the ATAL by a factor of 2–4 and compares to that of a plume coming from an advected moderate volcanic eruption. The stratospheric, trans-continental transport of this plume to the tropics and the related regional climate impact point to the importance of long-range dynamical interconnections of pollution sources.

The 2019/20 Australian wildfires generated a persistent smoke-charged vortex rising up to 35 km altitude

“…37 and ref. 4 Baseline and fire-perturbed simulations are carried out with different aerosol layers: the average OMPS-LP aerosols extinction coefficient profiles, for January and February 2019 (baseline simulation) and January and February 2020 (fire-perturbed simulation). The spectral variability of the aerosol extinction is modeled using the measured Ångström exponent from SAGE III for January 2020 (fireperturbed simulation) and typical background values inferred from SAGE III (baseline simulation).…”

“…With the PyroCb, intense fire-driven convection lifts combustion products in gaseous form as well as particulate matter including organic and black carbon, smoke aerosols and condensed water. The solar heating of the highly absorptive black carbon propels the smoke-laden air parcels upward 1 , which, combined with horizontal transport 3,4 , leads to a more efficient meridional dispersion of these aerosols and prolongs their stratospheric residence time 5 .…”

The unprecedented 2017–2018 stratospheric smoke event: decay phase and aerosol properties observed with the EARLINET

“…In contrast to liquid, spherical, less light-absorbing sulfuric acid droplets of volcanic origin, stratospheric smoke particles from the wildfires in 2017 were observed to be nonspherical Hu et al, 2019) and probably consisted of a solid core (black carbon (BC) aggregate) with nonspherical organic coating (Yu et al, 2019). In contrast to volcanic sulfuric acid particles, soot particles significantly absorb solar radiation (a direct effect on climate) and also influence the evolution of cirrus clouds by serving as INPs in heterogeneous ice nucleation processes (an indirect effect) (Hoose and Möhler, 2012;Kanji et al, 2017;Ullrich et al, 2017), unlike liquid sulfuric acid droplets which influence cirrus occurrence and evolution via homogeneous ice nucleation (Jensen and Toon, 1992;Sassen et al, 1995;Liu and Penner, 2002;Campbell et al, 2012). Homogeneous nucleation is the process in which droplets freeze (and no solid particle phase is involved).…”

Evaluation of the OMPS/LP stratospheric aerosol extinction product using SAGE III/ISS observations

“…Aerosol extinction at nine wavelengths (384.2, 448.5, 520.5, 601.6, 676.0, 756.0, 869.2, 1021.2, and 1544.0 nm) are provided by SAGE III/ISS from the surface or cloud top to an altitude of 45 km, with a vertical resolution of 0.5 km at the tangent point location. The SAGE III/ISS series of aerosol occultation measurements have been extensively evaluated and compared with other space-based instruments, and they have been found to have relatively high precision and accuracy (Thomason et al, 2010(Thomason et al, , 2018Bourassa et al, 2012;Kovilakam and Deshler, 2015;von Savigny et al, 2015;Rieger et al, 2018). In this work, we use SAGE III/ISS Version 5.1 data, including both sunrise and sunsets, which were collected during the period from June 2017 to May 2019.…”

“…The occurrence of PyroCbs triggered by intense wildfires in British Columbia, Canada, were reported on 12 August 2017. Within 2 months of injection, the plume can reach up to nearly 22 km (Peterson et al, 2018;Torres et al, 2020) and can be transported globally (Kloss et al, 2019). A before and after analysis was carried out to evaluate the performance of the LP algorithm following the stratospheric injection of carbonaceous aerosols.…”