scholarly journals Global all-sky shortwave direct radiative forcing of anthropogenic aerosols from combined satellite observations and GOCART simulations

2013 ◽  
Vol 118 (2) ◽  
pp. 655-669 ◽  
Author(s):  
Wenying Su ◽  
Norman G. Loeb ◽  
Gregory L. Schuster ◽  
Mian Chin ◽  
Fred G. Rose
Keyword(s):  
Radiative Forcing ◽  
Satellite Observations ◽  
Anthropogenic Aerosols ◽  
Direct Radiative Forcing

Direct radiative forcing of anthropogenic aerosols over oceans from satellite observations

2011 ◽  
Vol 28 (4) ◽  
pp. 973-984 ◽  
Author(s):  
Lin Chen ◽  
Guangyu Shi ◽  
Shiguang Qin ◽  
Su Yang ◽  
Peng Zhang
Keyword(s):  
Radiative Forcing ◽  
Satellite Observations ◽  
Anthropogenic Aerosols ◽  
Direct Radiative Forcing

scholarly journals Contrasting the direct radiative effect and direct radiative forcing of aerosols

2014 ◽  
Vol 14 (11) ◽  
pp. 5513-5527 ◽  
Author(s):  
C. L. Heald ◽  
D. A. Ridley ◽  
J. H. Kroll ◽  
S. R. H. Barrett ◽  
K. E. Cady-Pereira ◽  
...  
Keyword(s):  
Energy Balance ◽  
Radiative Forcing ◽  
Transport Model ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Radiative Effect ◽  
Chemical Transport Model ◽  
Anthropogenic Aerosols ◽  
Anthropogenic Aerosol ◽  
Direct Radiative Forcing

Abstract. The direct radiative effect (DRE) of aerosols, which is the instantaneous radiative impact of all atmospheric particles on the Earth's energy balance, is sometimes confused with the direct radiative forcing (DRF), which is the change in DRE from pre-industrial to present-day (not including climate feedbacks). In this study we couple a global chemical transport model (GEOS-Chem) with a radiative transfer model (RRTMG) to contrast these concepts. We estimate a global mean all-sky aerosol DRF of −0.36 Wm−2 and a DRE of −1.83 Wm−2 for 2010. Therefore, natural sources of aerosol (here including fire) affect the global energy balance over four times more than do present-day anthropogenic aerosols. If global anthropogenic emissions of aerosols and their precursors continue to decline as projected in recent scenarios due to effective pollution emission controls, the DRF will shrink (−0.22 Wm−2 for 2100). Secondary metrics, like DRE, that quantify temporal changes in both natural and anthropogenic aerosol burdens are therefore needed to quantify the total effect of aerosols on climate.

scholarly journals Radiative forcing by aerosols as derived from the AeroCom present-day and pre-industrial simulations

2006 ◽  
Vol 6 (3) ◽  
pp. 5095-5136 ◽  
Author(s):  
M. Schulz ◽  
C. Textor ◽  
S. Kinne ◽  
Y. Balkanski ◽  
S. Bauer ◽  
...  
Keyword(s):  
Mass Extinction ◽  
Radiative Forcing ◽  
Residence Times ◽  
Anthropogenic Aerosols ◽  
Annual Average ◽  
Lower Altitude ◽  
Extinction Coefficients ◽  
Clear Sky ◽  
Direct Radiative Forcing ◽  
The Difference

Abstract. Nine different global models with detailed aerosol modules have independently produced instantaneous direct radiative forcing due to anthropogenic aerosols. The anthropogenic impact is derived from the difference of two model simulations with identically prescribed aerosol emissions, one for present-day and one for pre-industrial conditions. The difference in the energy budget at the top of the atmosphere (ToA) yields a new harmonized estimate for the aerosol direct radiative forcing (RF) under all-sky conditions. On a global annual basis RF is –0.2 Wm-2, with a standard deviation of ±0.2 Wm-2. Anthropogenic nitrate and dust are not included in this estimate. No model shows a significant positive all-sky RF. The corresponding clear-sky RF is –0.6 Wm-2. The cloud-sky RF was derived based on all-sky and clear-sky RF and modelled cloud cover. It was significantly different from zero and ranged between –0.16 and +0.34 Wm-2. A sensitivity analysis shows that the total aerosol RF is influenced by considerable diversity in simulated residence times, mass extinction coefficients and most importantly forcing efficiencies (forcing per unit optical depth). Forcing efficiency differences among models explain most of the variability, mainly because all-sky forcing estimates require proper representation of cloud fields and the correct relative altitude placement between absorbing aerosol and clouds. The analysis of the sulphate RF shows that differences in sulphate residence times are compensated by opposite mass extinction coefficients. This is explained by more sulphate particle humidity growth and thus higher extinction in models with short-lived sulphate present at lower altitude and vice versa. Solar absorption within the atmospheric column is estimated at +0.85 Wm-2. The local annual average maxima of atmospheric forcing exceed +5 Wm-2 confirming the regional character of aerosol impacts on climate. The annual average surface forcing is –1.03 Wm-2.

scholarly journals Aerosol direct radiative forcing based on GEOS-Chem-APM and uncertainties

2012 ◽  
Vol 12 (1) ◽  
pp. 193-240 ◽  
Author(s):  
X. Ma ◽  
F. Yu ◽  
G. Luo
Keyword(s):  
Radiative Forcing ◽  
Global Climate ◽  
Size Composition ◽  
Transfer Model ◽  
Mixing State ◽  
Anthropogenic Aerosols ◽  
Anthropogenic Aerosol ◽  
Data Set ◽  
Direct Radiative Forcing ◽  
State Size

Abstract. Aerosol direct radiative forcing (DRF) plays an important role in global climate change but has a large uncertainty. Here we investigate aerosol DRF with GEOS-Chem-APM, a recently developed global aerosol microphysical model that is designed to capture key particle properties (size, composition, coating of primary particles by volatile species, etc.). The model, with comprehensive chemistry, microphysics and up-to-date emission inventories, is driven by assimilated meteorology, which is presumably more realistic compared to the model-predicted meteorology. For this study, the model is extended by incorporating a radiation transfer model. Optical properties are calculated using Mie theory, where the core-shell configuration could be treated with the refractive indices from the recently updated values available in the literature. The surface albedo is taken from MODIS satellite retrievals for the simulation year, in which the data set for the 8-day mean at 1 km resolution for 7 wavebands is provided. We derive the total and anthropogenic aerosol DRF, mainly focus on the results of anthropogenic aerosols, and then compare with those values reported in previous studies. In addition, we examine the anthropogenic aerosol DRF's dependence on several key factors, including the particle size of black carbon (BC) and primary organic carbon (POC), the density of BC and the mixing state. Our studies show that the anthropogenic aerosol DRF at top of atmosphere (TOA) for all sky is −0.41 W m−2. However, the sensitivity experiments suggest that the magnitude could vary from −0.08 W m−2 to −0.61 W m−2 depending on assumptions regarding the mixing state, size and density of particles.

scholarly journals Direct and semi-direct radiative forcing of smoke aerosols over clouds

2012 ◽  
Vol 12 (1) ◽  
pp. 139-149 ◽  
Author(s):  
E. M. Wilcox
Keyword(s):  
Atlantic Ocean ◽  
Radiative Forcing ◽  
Satellite Observations ◽  
Cloud Layer ◽  
Radiative Heating ◽  
Marine Stratocumulus ◽  
Direct Radiative Forcing ◽  
Stratocumulus Clouds ◽  
Direct Forcing ◽  
Positive Direct

Abstract. Observations from Earth observing satellites indicate that dark carbonaceous aerosols that absorb solar radiation are widespread in the tropics and subtropics. When these aerosols mix with clouds, there is generally a reduction of cloudiness owing to absorption of solar energy in the aerosol layer. Over the subtropical South Atlantic Ocean, where smoke from savannah burning in southern Africa resides above a persistent deck of marine stratocumulus clouds, radiative heating of the smoke layer leads to a thickening of the cloud layer. Here, satellite observations of the albedo of overcast scenes of 25 km2 size or larger are combined with additional satellite observations of clouds and aerosols to estimate the top-of-atmosphere direct radiative forcing attributable to presence of dark aerosol above bright cloud, and the negative semi-direct forcing attributable to the thickening of the cloud layer. The average positive direct radiative forcing by smoke over an overcast scene is 9.2±6.6 W m−2 for cases with an unambiguous signal of absorbing aerosol over cloud in passive ultraviolet remote sensing observations. However, cloud liquid water path is enhanced by 16.3±7.7 g m−2 across the range of values for sea surface temperature for cases of smoke over cloud. The negative radiative forcing associated with this semi-direct effect of smoke over clouds is estimated to be −5.9±3.5 W m−2. Therefore, the cooling associated with the semi-direct cloud thickening effect compensates for greater than 60 % of the direct radiative effect. Accounting for the frequency of occurrence of significant absorbing aerosol above overcast scenes leads to an estimate of the average direct forcing of 1.0±0.7 W m−2 contributed by these scenes averaged over the subtropical southeast Atlantic Ocean during austral winter. The regional average of the negative semi-direct forcing is −0.7±0.4 W m−2. Therefore, smoke aerosols overlaying the decks of overcast marine stratocumulus clouds considered here yield a small net positive radiative forcing, which results from the difference of two larger effects.

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