Pyrocumulonimbus affect average stratospheric aerosol composition

Abstract

Pyrocumulonimbus (pyroCb) are wildfire-generated convective clouds that can inject smoke directly into the stratosphere. PyroCb have been tracked for years, yet their apparent rarity and episodic nature lead to highly uncertain climate impacts. In situ measurements of pyroCb smoke reveal its distinctive and exceptionally stable aerosol properties and define the long-term influence of pyroCb activity on the stratospheric aerosol budget. Analysis of 13 years of airborne observations shows that pyroCb are responsible for 10 to 25% of the black carbon and organic aerosols in the “present-day” lower stratosphere, with similar impacts in both the North and South Hemispheres. These results suggest that, should pyroCb increase in frequency and/or magnitude in future climates, they could generate dominant trends in stratospheric aerosol.

The Dynamics of Megafire Smoke Plumes in Climate Models: Why a Converged Solution Matters for Physical Interpretations

“…Utilizing the same injection height, under-resolved simulations at 1.0° or 2.0° grid spacing would require a large and likely artificial increase in the BC fraction/mass to produce the same stratospheric lifetime as the well-resolved 0.25° simulation. The lower BC mass fractions identified in this paper are consistent with recent observations of the BC17 smoke plume described in Katich et al (2023) after accounting for sampling uncertainty and the larger area represented in the model.…”

“…A mean particle radius of 350 nm is used for all simulations and is held fixed. This particle radius is motivated by observations of thick coatings in upper tropospheric smokes plumes (Ditas et al, 2018;Katich et al, 2023). Similarities and differences of the smoke plume initialization described here with that from prior work can be found in the introduction section.…”

“…Recently, aircraft observations of the BC17 plume have been reported in Katich et al (2023), focused on thickly coated BC. They report BC fractions of 2.8% ± 48% (01 October 2017 over a 767 s interception) and 1.24% ± 48% (25 October 2017 over 2832 s interception).…”

“…They report BC fractions of 2.8% ± 48% (01 October 2017 over a 767 s interception) and 1.24% ± 48% (25 October 2017 over 2832 s interception). These flight segments imply an average of 1.57% ± 48% BC fraction in the sampled 1 month old smoke (Katich et al, 2023). It is important to note that the smoke plumes are heterogeneous and the aircraft only samples a limited region of these plumes.…”

Insights into Pyrocumulus aerosol composition: black carbon content and organic vapor condensation

“…These include changes in its mixing state, OA coating thickness, and structure, which influence BC's radiative properties and atmospheric lifetime. 7–12 Moreover, solar heating by BC absorption increases self-lofting of aerosol and consequently the higher peak altitude and longer lifetime of PyroCu smoke plumes. 13…”