Characterization of the radiative impact of aerosols on CO₂ and energy fluxes in the Amazon deforestation arch using artificial neural networks

In vegetation canopies with complex architectures, diffuse solar radiation can enhance carbon assimilation through photosynthesis because isotropic light is able to reach deeper layers of the canopy. Although this effect has been studied in the past decade, the mechanisms and impacts of this enhancement over South America remain poorly understood. Over the Amazon deforestation arch large amounts of aerosols are released into the atmosphere due to biomass burning, which provides an ideal scenario for further investigation of this phenomenon in the presence of canopies with complex architecture. In this paper, the relation of aerosol optical depth and surface fluxes of mass and energy are evaluated over three study sites with artificial neural networks and radiative transfer modeling. Results indicate a significant effect of the aerosol on the flux of carbon dioxide between the vegetation and the atmosphere, as well as on energy exchange, including that surface fluxes are sensitive to second-order radiative impacts of aerosols on temperature, humidity, and friction velocity. CO₂ exchanges increased in the presence of aerosol in up to 55 % in sites with complex canopy architecture. A decrease of approximately 12 % was observed for a site with shorter vegetation. Energy fluxes were negatively impacted by aerosols over all study sites

Evaluation of CO2, Sensible and Latent Heat Turbulent Fluxes as Function of Aerosol Optical Depth over the Deforestation Arch in the Legal Brazilian Amazon

Em dosséis com arquitetura foliar complexa, a radiação solar difusa pode potencializar a capacidade fotossintética, porque os penetra de modo mais eficiente. Apesar dos diversos estudos realizados nesse sentido em diferentes regiões do globo, os mecanismos e impactos do efeito da fertilização difusa sobre a América do Sul ainda continuam sendo pouco conhecidos. O Arco do Desflorestamento da Amazônia é um cenário ideal para sua maior investigação, tanto pela presença de complexos ecossistemas, quanto pela grande carga de aerossóis lançada para a atmosfera, em decorrência da queima de biomassa. Um estudo baseado em três diferentes localidades do Arco do Desflorestamento da Amazônia foi conduzido, a fim de relacionar a profundidade óptica dos aerossóis com alguns fluxos de superfície. Os resultados mostraram efeitos significativos da presença dos aerossóis tanto na troca de gás carbônico entre a vegetação e a atmosfera, quanto na troca de energia. Ainda, os fluxos mostraram ser sensíveis também às mudanças na temperatura, umidade e vento, além da influência do próprio ciclo diurno. Em cenários hipotéticos, foi possível isolar apenas o efeito do aerossol. O comportamento do fluxo de gás carbônico à presença dos aerossóis não foi o mesmo para as três localidades, o que indica uma grande dependência do fenômeno com as características da vegetação local. Na Reserva Biológica do Jaru e Ilha do Bananal, as trocas de gás carbônico entre a atmosfera e a superfície são favorecidas na presença de aerossóis, podendo atingir valores até 55% maiores em Jaru. Entretanto, Sinop apresentou uma redução de aproximadamente 12% no valor médio do fluxo de gás carbônico, para o período avaliado. Os fluxos de energia mostraram ser afetados negativamente pela presença dos aerossóis. Na Ilha do Bananal, a média do fluxo de calor sensível em cenários sem aerossóis foi em torno de 60% maior, e de até 13% maior para o fluxo de calor latente em Sinop. Devido aos processos de absorção e espalhamento da radiação solar pelos aerossóis, menos energia atinge a superfície e, portanto, há menos disponibilidade para a realização de tais trocas, como esperado.In complex architecture canopies, the diffuse solar radiation can enhance photosynthetic capacity, as it penetrates more efficiently on them. Although several studies have been conducted on this topic over the world, the mechanisms and impacts of the \"diffuse fertilization effect\" over South America still remains poorly understood. The Amazon Deforestation Arch provides an ideal scenario for its further investigation, by the presence of complex ecosystems and by the large amounts of aerosols released into the atmosphere due to biomass burning. A study based on three different sites in the Amazon Deforestation Arch was conducted in order to relate the aerosol optical depth with some surface fluxes. The results showed significant effects of the aerosol presence in both, the exchange of carbon dioxide between the vegetation and the atmosphere, and the energy exchange. Still, the fluxes also showed to be sensitive to changes in temperature, humidity and wind velocities, as well as the influence of the diurnal cycle itself. In hypothetical scenarios, it was possible to isolate only the aerosol effect. The carbon dioxide flux behavior due to the aerosol presence was not the same for all the three locations, showing that it depends on the local vegetation characteristics. At the Jaru Biological Reserve and Bananal Island, the carbonic gas exchanges between the atmosphere and the surface increased under the aerosol presence, achieving values up to 55% higher in Jaru. However, Sinop showed a decrease by approximately 12% in the average value of the carbon dioxide flux for the evaluated period. Energy fluxes showed to be negatively affected by the presence of aerosols. In the Bananal Island the average of sensitive heat flux in scenarios without aerosols was around 60% higher, and up to 13% higher for the latent heat flux in Sinop. Due to absorption and scattering of solar radiation by the aerosols, less energy reaches the surface, and therefore there is less availability to perform such exchanges, as expected

Improving the treatment of vegetation canopy architecture in radiative transfer schemes

Addressing the impact of vegetation architecture on the treatment of shortwave radiation in land surface models (LSMs) is important for accurate weather forecast and climate predictions. The study of the carbon budget is also impacted by vegetation architecture because shortwave radiation is used by plants to photosynthesise. Three pieces of research are presented in this thesis: the implementation and evaluation of different parameterisations of vegetation architecture in a commonly used radiative transfer scheme; analysis of the impact of Sun zenith angular variability on vegetation structural parameters including the effect that these parameters have on Gross Primary Productivity (GPP) at site level; and a study on how the simulation of global carbon assimilation is impacted when considering vegetation architecture with satellite derived data sets. Neglecting canopy heterogeneity in radiative transfer schemes leads to significant uncertainties in shortwave radiation absorption and reflectance. The best agreement between detailed 3D radiative transfer schemes and a parameterised 1D version that accounts for vegetation architecture heterogeneity is given when considering zenith angular variability of the parameters. The major impacts on shortwave radiation distribution along the vertical axis are found at the bottom layers of the canopy, which absorbs more radiation when structure is considered. Further impacts on photosynthesis are evaluated at site level with digital hemispherical photography and eddy covariance measurements, and at global level with satellite data and global modelling. Impacts on GPP are dependent on the vertical distribution of the photosynthesis limiting regimes and the variation of the structural parameters with Sun zenith angle is more important over sites with denser foliage than sites with sparser foliage. At global level, prediction of GPP increases by 5.53 ± 1.02 PgC.yr−1 when considering canopy structure, with a strong signal in the tropics. This work establishes the importance of considering vegetation canopy architecture in land surface modelling and predicts that current values of global GPP might be underestimated by LSM

Avaliação da fração de radiação fotossinteticamente ativa absorvida pela floresta tropical primária na Amazônia durante a estação seca dos anos de 2002 e 2007

The fraction of absorbed photosynthetically active radiation (fAPAR) by vegetation is an important variable in modeling biosphere-atmosphere interaction, for example, to estimate carbon assimilation by vegetation. This determination from surface measurements is limited to extremely small areas. The use of remote sensing techniques on board artificial satellites represents an important alternative for obtaining such a fraction on a global scale and long term. However, because of it, satellite procurement be made indirectly, based on models of vegetation, radiative transfer algorithms and mainly due to the influence of atmospheric transmission of solar radiation at the top of the atmosphere to the surface and vice versa, it is crucial validation from other techniques. This work is focused on the validation of fAPAR derived from measurements of the MODIS (Moderate Resolution Imaging Radiometer) aboard the Terra and Aqua satellites from estimates made in comparison with the surface during two intensive field experiments conducted during the dry season of 2002 and 2007 in the Biological Reserve Jaru, RO Brazil.Pages: 6019-602

Avaliação da fração de radiação fotossinteticamente ativa absorvida pela floresta tropical primária na Amazônia durante a estação seca dos anos de 2002 e 2007

The fraction of absorbed photosynthetically active radiation (fAPAR) by vegetation is an important variable in modeling biosphere-atmosphere interaction, for example, to estimate carbon assimilation by vegetation. This determination from surface measurements is limited to extremely small areas. The use of remote sensing techniques on board artificial satellites represents an important alternative for obtaining such a fraction on a global scale and long term. However, because of it, satellite procurement be made indirectly, based on models of vegetation, radiative transfer algorithms and mainly due to the influence of atmospheric transmission of solar radiation at the top of the atmosphere to the surface and vice versa, it is crucial validation from other techniques. This work is focused on the validation of fAPAR derived from measurements of the MODIS (Moderate Resolution Imaging Radiometer) aboard the Terra and Aqua satellites from estimates made in comparison with the surface during two intensive field experiments conducted during the dry season of 2002 and 2007 in the Biological Reserve Jaru, RO Brazil.Pages: 6019-602

Characterization of the radiative impact of aerosols on CO2 and energy fluxes in the Amazon deforestation arch using artificial neural networks

In vegetation canopies with complex architectures, diffuse solar radiation can enhance carbon assimilation through photosynthesis because isotropic light is able to reach deeper layers of the canopy. Although this effect has been studied in the past decade, the mechanisms and impacts of this enhancement over South America remain poorly understood. Over the Amazon deforestation arch large amounts of aerosols are released into the atmosphere due to biomass burning, which provides an ideal scenario for further investigation of this phenomenon in the presence of canopies with complex architecture. In this paper, the relation of aerosol optical depth and surface fluxes of mass and energy are evaluated over three study sites with artificial neural networks and radiative transfer modeling. Results indicate a significant effect of the aerosol on the flux of carbon dioxide between the vegetation and the atmosphere, as well as on energy exchange, including that surface fluxes are sensitive to second-order radiative impacts of aerosols on temperature, humidity, and friction velocity. CO2 exchanges increased in the presence of aerosol in up to 55 % in sites with complex canopy architecture. A decrease of approximately 12 % was observed for a site with shorter vegetation. Energy fluxes were negatively impacted by aerosols over all study sites.. © 2020 BMJ Publishing Group. All rights reserved

Characterization of the radiative impact of aerosols on CO2 and energy fluxes in the Amazon deforestation arch using artificial neural networks

In vegetation canopies with complex architectures, diffuse solar radiation can enhance carbon assimilation through photosynthesis because isotropic light is able to reach deeper layers of the canopy. Although this effect has been studied in the past decade, the mechanisms and impacts of this enhancement over South America remain poorly understood. Over the Amazon deforestation arch large amounts of aerosols are released into the atmosphere due to biomass burning, which provides an ideal scenario for further investigation of this phenomenon in the presence of canopies with complex architecture. In this paper, the relation of aerosol optical depth and surface fluxes of mass and energy are evaluated over three study sites with artificial neural networks and radiative transfer modeling. Results indicate a significant effect of the aerosol on the flux of carbon dioxide between the vegetation and the atmosphere, as well as on energy exchange, including that surface fluxes are sensitive to second-order radiative impacts of aerosols on temperature, humidity, and friction velocity. CO2 exchanges increased in the presence of aerosol in up to 55 % in sites with complex canopy architecture. A decrease of approximately 12 % was observed for a site with shorter vegetation. Energy fluxes were negatively impacted by aerosols over all study sites.. © 2020 BMJ Publishing Group. All rights reserved