scholarly journals Absorbing Refractive Index and Direct Radiative Forcing of Atmospheric Brown Carbon over Gangetic Plain

2017 ◽  
Vol 2 (1) ◽  
pp. 31-37 ◽  
Author(s):  
P. M. Shamjad ◽  
R. V. Satish ◽  
Navaneeth M. Thamban ◽  
N. Rastogi ◽  
S. N. Tripathi
Keyword(s):  
Refractive Index ◽  
Radiative Forcing ◽  
Gangetic Plain ◽  
Brown Carbon ◽  
Direct Radiative Forcing

Contribution of Brown Carbon to Direct Radiative Forcing over the Indo-Gangetic Plain

2015 ◽  
Vol 49 (17) ◽  
pp. 10474-10481 ◽  
Author(s):  
P. M. Shamjad ◽  
S. N. Tripathi ◽  
Ravi Pathak ◽  
M. Hallquist ◽  
Antti Arola ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Gangetic Plain ◽  
Brown Carbon ◽  
Direct Radiative Forcing ◽  
Indo Gangetic Plain

scholarly journals Exploiting simultaneous observational constraints on mass and absorption to estimate the global direct radiative forcing of black carbon and brown carbon

2014 ◽  
Vol 14 (20) ◽  
pp. 10989-11010 ◽  
Author(s):  
X. Wang ◽  
C. L. Heald ◽  
D. A. Ridley ◽  
J. P. Schwarz ◽  
J. R. Spackman ◽  
...  
Keyword(s):  
Optical Properties ◽  
Black Carbon ◽  
Biomass Burning ◽  
Radiative Forcing ◽  
Model Simulation ◽  
Anthropogenic Sources ◽  
Absorption Enhancement ◽  
Brown Carbon ◽  
Direct Radiative Forcing ◽  
Improved Model

Abstract. Atmospheric black carbon (BC) is a leading climate warming agent, yet uncertainties on the global direct radiative forcing (DRF) remain large. Here we expand a global model simulation (GEOS-Chem) of BC to include the absorption enhancement associated with BC coating and separately treat both the aging and physical properties of fossil-fuel and biomass-burning BC. In addition we develop a global simulation of brown carbon (BrC) from both secondary (aromatic) and primary (biomass burning and biofuel) sources. The global mean lifetime of BC in this simulation (4.4 days) is substantially lower compared to the AeroCom I model means (7.3 days), and as a result, this model captures both the mass concentrations measured in near-source airborne field campaigns (ARCTAS, EUCAARI) and surface sites within 30%, and in remote regions (HIPPO) within a factor of 2. We show that the new BC optical properties together with the inclusion of BrC reduces the model bias in absorption aerosol optical depth (AAOD) at multiple wavelengths by more than 50% at AERONET sites worldwide. However our improved model still underestimates AAOD by a factor of 1.4 to 2.8 regionally, with the largest underestimates in regions influenced by fire. Using the RRTMG model integrated with GEOS-Chem we estimate that the all-sky top-of-atmosphere DRF of BC is +0.13 Wm−2 (0.08 Wm−2 from anthropogenic sources and 0.05 Wm−2 from biomass burning). If we scale our model to match AERONET AAOD observations we estimate the DRF of BC is +0.21 Wm−2, with an additional +0.11 Wm−2 of warming from BrC. Uncertainties in size, optical properties, observations, and emissions suggest an overall uncertainty in BC DRF of −80%/+140%. Our estimates are at the lower end of the 0.2–1.0 Wm−2 range from previous studies, and substantially less than the +0.6 Wm−2 DRF estimated in the IPCC 5th Assessment Report. We suggest that the DRF of BC has previously been overestimated due to the overestimation of the BC lifetime (including the effect on the vertical profile) and the incorrect attribution of BrC absorption to BC.

scholarly journals Exploiting simultaneous observational constraints on mass and absorption to estimate the global direct radiative forcing of black carbon and brown carbon

2014 ◽  
Vol 14 (11) ◽  
pp. 17527-17583 ◽  
Author(s):  
X. Wang ◽  
C. L. Heald ◽  
D. A. Ridley ◽  
J. P. Schwarz ◽  
J. R. Spackman ◽  
...  
Keyword(s):  
Optical Properties ◽  
Black Carbon ◽  
Biomass Burning ◽  
Radiative Forcing ◽  
Model Simulation ◽  
Anthropogenic Sources ◽  
Absorption Enhancement ◽  
Brown Carbon ◽  
Direct Radiative Forcing ◽  
Improved Model

Abstract. Atmospheric black carbon (BC) is a leading climate warming agent, yet uncertainties on the global direct radiative forcing (DRF) remain large. Here we expand a global model simulation (GEOS-Chem) of BC to include the absorption enhancement associated with BC coating and separately treat both the aging and physical properties of fossil fuel and biomass burning BC. In addition we develop a global simulation of Brown Carbon (BrC) from both secondary (aromatic) and primary (biomass burning and biofuel) sources. The global mean lifetime of BC in this simulation (4.4 days) is substantially lower compared to the AeroCom I model means (7.3 days), and as a result, this model captures both the mass concentrations measured in near-source airborne field campaigns (ARCTAS, EUCAARI) and surface sites within 30%, and in remote regions (HIPPO) within a factor of two. We show that the new BC optical properties together with the inclusion of BrC reduces the model bias in Absorption Aerosol Optical Depth (AAOD) at multiple wavelengths by more than 50% at AERONET sites worldwide. However our improved model still underestimates AAOD by a factor of 1.4 to 2.8 regionally, with largest underestimates in regions influenced by fire. Using the RRTMG model integrated with GEOS-Chem we estimate that the all-sky top-of-atmosphere DRF of BC is +0.13 W m−2 (0.08 W m−2 from anthropogenic sources and 0.05 W m−2 from biomass burning). If we scale our model to match AERONET AAOD observations we estimate the DRF of BC is +0.21 W m−2, with an additional +0.11 W m−2 of warming from BrC. Uncertainties in size, optical properties, observations, and emissions suggest an overall uncertainty in BC DRF of −80% / +140%. Our estimates are at the lower end of the 0.2–1.0 W m−2 range from previous studies, and substantially less than the +0.6 W m−2 DRF estimated in the IPCC 5th Assessment Report. We suggest that the DRF of BC has previously been overestimated due to the overestimation of the BC lifetime and the incorrect attribution of BrC absorption to BC.

scholarly journals Estimates of direct radiative forcing due to aerosols from the MERRA-2 reanalysis over the Amazon region

2018 ◽  
Author(s):  
Brunna Penna ◽  
Dirceu Herdies ◽  
Simone Costa
Keyword(s):  
Radiative Forcing ◽  
Reanalysis Data ◽  
Amazon Region ◽  
Reference State ◽  
Aerosol Radiative Forcing ◽  
Aerosol Loading ◽  
Direct Radiative Forcing ◽  
Direct Forcing ◽  
The Difference ◽  
Natural Aerosols

Abstract. Sixteen years of analysis of clear-sky direct aerosol radiative forcing is presented for the Amazon region, with calculations of AERONET network, MODIS sensor and MERRA-2 reanalysis data. The results showed that MERRA-2 reanalysis is an excellent tool for calculating and providing the spatial distribution of aerosol direct radiative forcing. In addition, the difference between considering the reference state of the atmosphere without aerosol loading and with natural aerosol to obtain the aerosol direct radiative forcing is discussed. During the dry season, the monthly average direct forcing at the top of atmosphere varied from −9.60 to −4.20 Wm−2, and at the surface, it varied from −29.81 to −9.24 Wm−2, according to MERRA-2 reanalysis data and the reference state of atmosphere without aerosol loading. Already with the state of reference being the natural aerosols, the average direct forcing at the top of atmosphere varied from −5.15 to −1.18 Wm−2, and at the surface, it varied from −21.28 to −5.25 Wm−2; this difference was associated with the absorption of aerosols.

scholarly journals Impact of Desert Dust Radiative Forcing on Sahel Precipitation: Relative Importance of Dust Compared to Sea Surface Temperature Variations, Vegetation Changes, and Greenhouse Gas Warming

2007 ◽  
Vol 20 (8) ◽  
pp. 1445-1467 ◽  
Author(s):  
Masaru Yoshioka ◽  
Natalie M. Mahowald ◽  
Andrew J. Conley ◽  
William D. Collins ◽  
David W. Fillmore ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
North Africa ◽  
Radiative Forcing ◽  
Sea Surface ◽  
Desert Dust ◽  
Direct Radiative Forcing ◽  
Sahel Region ◽  
Precipitation Reduction ◽  
Sahel Precipitation

Abstract The role of direct radiative forcing of desert dust aerosol in the change from wet to dry climate observed in the African Sahel region in the last half of the twentieth century is investigated using simulations with an atmospheric general circulation model. The model simulations are conducted either forced by the observed sea surface temperature (SST) or coupled with the interactive SST using the Slab Ocean Model (SOM). The simulation model uses dust that is less absorbing in the solar wavelengths and has larger particle sizes than other simulation studies. As a result, simulations show less shortwave absorption within the atmosphere and larger longwave radiative forcing by dust. Simulations using SOM show reduced precipitation over the intertropical convergence zone (ITCZ) including the Sahel region and increased precipitation south of the ITCZ when dust radiative forcing is included. In SST-forced simulations, on the other hand, significant precipitation changes are restricted to over North Africa. These changes are considered to be due to the cooling of global tropical oceans as well as the cooling of the troposphere over North Africa in response to dust radiative forcing. The model simulation of dust cannot capture the magnitude of the observed increase of desert dust when allowing dust to respond to changes in simulated climate, even including changes in vegetation, similar to previous studies. If the model is forced to capture observed changes in desert dust, the direct radiative forcing by the increase of North African dust can explain up to 30% of the observed precipitation reduction in the Sahel between wet and dry periods. A large part of this effect comes through atmospheric forcing of dust, and dust forcing on the Atlantic Ocean SST appears to have a smaller impact. The changes in the North and South Atlantic SSTs may account for up to 50% of the Sahel precipitation reduction. Vegetation loss in the Sahel region may explain about 10% of the observed drying, but this effect is statistically insignificant because of the small number of years in the simulation. Greenhouse gas warming seems to have an impact to increase Sahel precipitation that is opposite to the observed change. Although the estimated values of impacts are likely to be model dependent, analyses suggest the importance of direct radiative forcing of dust and feedbacks in modulating Sahel precipitation.

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