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Abstract The ocean’s major circulation system, the Atlantic Meridional Overturning Circulation (AMOC), is slowing down. Such weakening is consistent with warming associated with increasing greenhouse gases, as well as with recent decreases in industrial aerosol pollution. The impact of biomass burning aerosols on the AMOC, however, remains unexplored. Here, we use the Community Earth System Model version 1 Large Ensemble to quantify the impact of both aerosol types on the AMOC. Despite relatively small changes in North Atlantic biomass burning aerosols, significant AMOC evolution occurs, including weakening from 1920 to ~1970 followed by AMOC strengthening. These changes are largely out of phase relative to the corresponding AMOC evolution under industrial aerosols. AMOC responses are initiated by thermal changes in sea surface density flux due to altered shortwave radiation. An additional dynamical mechanism involving the North Atlantic sea-level pressure gradient is important under biomass-burning aerosols. AMOC-induced ocean salinity flux convergence acts as a positive feedback. Our results show that biomass-burning aerosols reinforce early 20th-century AMOC weakening associated with greenhouse gases and also partially mute industrial aerosol impacts on the AMOC. Recent increases in wildfires suggest biomass-burning aerosols may be an important driver of future AMOC variability.
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Simulating the forest fire plume dispersion, chemistry, and aerosol formation using SAM-ASP version 1.0
Abstract. Biomass burning is a major source of trace gases andaerosols that can ultimately impact health, air quality, and climate.Global and regional-scale three-dimensional Eulerian chemical transportmodels (CTMs) use estimates of the primary emissions from fires and canunphysically mix them across large-scale grid boxes, leading to incorrectestimates of the impact of biomass burning events. On the other hand,plume-scale process models allow for explicit simulation and examination ofthe chemical and physical transformations of trace gases and aerosols withinbiomass burning smoke plumes, and they may be used to developparameterizations of this aging process for coarser grid-scale models. Herewe describe the coupled SAM-ASP plume-scale process model, which consists ofcoupling the large-eddy simulation model, the System for AtmosphericModelling (SAM), with the detailed gas and aerosol chemistry model, theAerosol Simulation Program (ASP). We find that the SAM-ASP version 1.0 modelis able to correctly simulate the dilution of CO in a California chaparralsmoke plume, as well as the chemical loss of NOx, HONO, and NH3within the plume, the formation of PAN and O3, the loss of OA, and thechange in the size distribution of aerosols as compared to measurements andprevious single-box model results. The newly coupled model is able tocapture the cross-plume vertical and horizontal concentration gradients asthe fire plume evolves downwind of the emission source. The integration andevaluation of SAM-ASP version 1.0 presented here will support thedevelopment of parameterizations of near-source biomass burning chemistrythat can be used to more accurately simulate biomass burning chemical andphysical transformations of tracegases and aerosols within coarser grid-scale CTMs.
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- PAR ID:
- 10211178
- Date Published:
- Journal Name:
- Geoscientific Model Development
- Volume:
- 13
- Issue:
- 9
- ISSN:
- 1991-9603
- Page Range / eLocation ID:
- 4579 to 4593
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/gmd-13-4579-2020
