Modeling the South American regional smoke plume: aerosol optical depth variability and surface shortwave flux perturbation

Abstract

Intra-seasonal variability of smoke aerosol optical depth (AOD) and downwelling solar irradiance at the surface during the 2002 biomass burning season in South America was modeled using the Coupled Chemistry-Aerosol-Tracers Transport model with the Brazilian developments on the Regional Atmospheric Modeling System (CCATT-BRAMS). Measurements of total and fine mode fraction (FMF) AOD from the AErosol RObotic NETwork (AERONET) and solar irradiance at the surface from the Solar Radiation Network (SolRad-NET) were used to evaluate model results. In general, the major features associated with AOD evolution over the southern part of the Amazon basin and cerrado ecosystem are captured by the model. The main discrepancies were found for high aerosol loading events. In the northeastern portion of the Amazon basin the model systematically underestimated total AOD, as expected, since smoke contribution is not dominant as it is in the southern portion and emissions other than smoke were not considered in the simulation. Better agreement was obtained comparing the model results with observed FMF AOD, which pointed out the relevance of coarse mode aerosol emission in that region. Likewise, major discrepancies over cerrado during high AOD events were found to be associated with coarse mode aerosol omission in our model. The issue of high aerosol loading events in the southern part of the Amazon was related to difficulties in predicting the smoke AOD field, which was discussed in the context of emissions shortcomings. The Cuiabá cerrado site was the only one where the highest quality AERONET data were unavailable for both total and FMF AOD. Thus, lower quality data were used. Root-mean-square error (RMSE) between the model and observed FMF AOD decreased from 0.34 to 0.19 when extreme AOD events (FMF AOD_{550 nm} ≥ 1.0) and Cuiabá were excluded from the analysis. Downward surface solar irradiance comparisons also followed similar trends when extreme AOD were excluded. This highlights the need to improve modelling of the regional smoke plume in order to enhance the accuracy of the radiative energy budget. An aerosol optical model based on the mean intensive properties of smoke from the southern part of the Amazon basin produced a radiative flux perturbation efficiency (RFPE) of −158 Wm⁻²/AOD_{550 nm} at noon. This value falls between −154 Wm⁻²/AOD_{550 nm} and −187 Wm⁻²/AOD_{550 nm}, the range obtained when spatially varying optical models were considered. The 24 h average surface radiative flux perturbation over the biomass burning season varied from −55 Wm⁻² close to smoke sources in the southern part of the Amazon basin and cerrado to −10 Wm⁻² in remote regions of the southeast Brazilian coast

Modeling the radiative effects of biomass burning aerosols on carbon fluxes in the Amazon region

“…Consistent with previous studies (Freitas et al, 2005(Freitas et al, , 2017Longo et al, 2010Longo et al, , 2013Rosário et al, 2013;Moreira et al, 2013), BRAMS performed well while modeling the meteorology and aerosol biomass burning emission, transport, and removal processes in Amazonia, which has resulted in accurate simulation of the major features of AOD variability associated with the regional biomass burning plume over South America. The model results for surface temperature, rainfall, and AOD were once again in agreement with observations for the 2010 dry season case study, representing the main characteristics of the spatial distribution and the diurnal cycle of temperature and precipitation.…”

“…The radiation scheme is a modified version of the Community Aerosol and Radiation Model for Atmospheres (CARMA; Toon et al, 1988), which includes the aerosolradiation interaction with feedback to the model heating rates Rosário et al, 2013). In addition, we included in CARMA a parameterization to calculate the diffuse fraction of solar irradiance specific to biomass burning aerosols in Amazonia.…”

Local and Regional Contributions to Black Carbon Aerosols in a Mid-Sized City in Southern Brazil

“…Prins et al (1998) found that the majority of the biomass fires observed in South America between 0 to 40°S and 35 to 75°W occurred in August and September, and recent data reported 444,059 fire foci nationwide in August andSeptember 2014 (INPE, 2015). The onset of the rainy season in October diminishes the fire foci (58,290 in the period December 2014-January 2015) and the increase of the aerosol optical depth is more related to smoke bursts due to local emissions (Rosário et al, 2013). We chose two subperiods within UTF dry and UTF wet , and combined location of fire foci in South America (INPE, 2015) with 120-h air mass backtrajectories calculated with HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory) model (Draxler and Rolph, 2011) arriving in Londrina at 500 m above terrain level with 1-hour interval.…”

Long-term observations of cloud condensation nuclei in the Amazon rain forest – Part 2: Variability and characteristic differences under near-pristine, biomass burning, and long-range transport conditions

“…As mentioned above, the incoming solar radiation was dimmed compared to the days before and after this BB event. Furthermore, the cloud fraction decreased, which might result from stabilizing the atmosphere due to increased absorption of solar radiation in and above the boundary layer (Koren et al, 2004;Rosenfeld et al, 2008;Rosario et al, 2013). A detailed investigation of the direct radiative forcing and the modification of cloud properties by aerosol particles in the Amazon rain forest are clearly beyond the 15 scope of this study.…”