scholarly journals Estimates of aerosol radiative forcing from the MACC re-analysis

2013 ◽  
Vol 13 (4) ◽  
pp. 2045-2062 ◽  
Author(s):  
N. Bellouin ◽  
J. Quaas ◽  
J.-J. Morcrette ◽  
O. Boucher
Keyword(s):  
Standard Deviation ◽  
Radiative Forcing ◽  
Cloud Droplet ◽  
Anthropogenic Aerosols ◽  
Medium Range Weather Forecast ◽  
Aerosol Absorption ◽  
Best Estimate ◽  
Satellite Retrievals ◽  
Direct Radiative Forcing ◽  
Indirect Radiative Forcing

Abstract. The European Centre for Medium-range Weather Forecast (ECMWF) provides an aerosol re-analysis starting from year 2003 for the Monitoring Atmospheric Composition and Climate (MACC) project. The re-analysis assimilates total aerosol optical depth retrieved by the Moderate Resolution Imaging Spectroradiometer (MODIS) to correct for model departures from observed aerosols. The re-analysis therefore combines satellite retrievals with the full spatial coverage of a numerical model. Re-analysed products are used here to estimate the shortwave direct and first indirect radiative forcing of anthropogenic aerosols over the period 2003–2010, using methods previously applied to satellite retrievals of aerosols and clouds. The best estimate of globally-averaged, all-sky direct radiative forcing is −0.7 ± 0.3 Wm−2. The standard deviation is obtained by a Monte-Carlo analysis of uncertainties, which accounts for uncertainties in the aerosol anthropogenic fraction, aerosol absorption, and cloudy-sky effects. Further accounting for differences between the present-day natural and pre-industrial aerosols provides a direct radiative forcing estimate of −0.4 ± 0.3 Wm−2. The best estimate of globally-averaged, all-sky first indirect radiative forcing is −0.6 ± 0.4 Wm−2. Its standard deviation accounts for uncertainties in the aerosol anthropogenic fraction, and in cloud albedo and cloud droplet number concentration susceptibilities to aerosol changes. The distribution of first indirect radiative forcing is asymmetric and is bounded by −0.1 and −2.0 Wm−2. In order to decrease uncertainty ranges, better observational constraints on aerosol absorption and sensitivity of cloud droplet number concentrations to aerosol changes are required.

scholarly journals Estimates of aerosol radiative forcing from the MACC re-analysis

2012 ◽  
Vol 12 (8) ◽  
pp. 20073-20111 ◽  
Author(s):  
N. Bellouin ◽  
J. Quaas ◽  
J.-J. Morcrette ◽  
O. Boucher
Keyword(s):  
Radiative Forcing ◽  
Cloud Droplet ◽  
Anthropogenic Aerosols ◽  
Medium Range Weather Forecast ◽  
Aerosol Absorption ◽  
Best Estimate ◽  
Spatial Coverage ◽  
Satellite Retrievals ◽  
Direct Radiative Forcing ◽  
Indirect Radiative Forcing

Abstract. The European Centre for Medium-range Weather Forecast (ECMWF) provides an aerosol re-analysis starting from year 2003 for the Monitoring Atmospheric Composition and Climate (MACC) project. The re-analysis assimilates total aerosol optical depth retrieved by the Moderate Resolution Imaging Spectroradiometer (MODIS) to correct for model departures from observed aerosols. The re-analysis therefore combines satellite retrievals with the full spatial coverage of a numerical model. Re-analysed products are used here to estimate the shortwave direct and first indirect radiative forcing of anthropogenic aerosols over the period 2003–2010, using methods previously applied to satellite retrievals of aerosols and clouds. The best estimate of globally-averaged, all-sky direct radiative forcing is −0.5 Wm−2. Accounting for uncertainties in the aerosol anthropogenic fraction, aerosol absorption, and cloudy-sky effects, results in the direct radiative forcing being bounded by −0.8 and 0 Wm−2. Further accounting for differences between the present-day natural and pre-industrial aerosols provides a direct radiative forcing estimate in the range −0.5 to 0 Wm−2, with a best estimate of −0.3 Wm−2. The best estimate of globally-averaged, all-sky first indirect radiative forcing is −0.4 Wm−2. Accounting for uncertainties in the aerosol anthropogenic fraction, cloud albedo, and cloud droplet number concentration susceptibility to aerosol changes, lower and upper bounds of the first indirect radiative forcing are −2.1 Wm−2 and −0.1 Wm−2 In order to decrease uncertainty ranges, better observational constraints on aerosol absorption and susceptibility of cloud droplet number concentrations to aerosol changes are required.

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 Influence of anthropogenic aerosols on the Asian monsoon: a case study using the WRF-Chem model

2013 ◽  
Vol 13 (8) ◽  
pp. 21383-21425 ◽  
Author(s):  
X. Jiang ◽  
M. C. Barth ◽  
C. Wiedinmyer ◽  
S. T. Massie
Keyword(s):  
East Asia ◽  
Radiative Forcing ◽  
Asian Monsoon ◽  
Anthropogenic Activities ◽  
Cloud Droplet ◽  
Cloud Base ◽  
Monsoon Precipitation ◽  
Anthropogenic Aerosols ◽  
Source Regions ◽  
Local Emissions

Abstract. Aerosols, in particular those related to anthropogenic activities, including black carbon, organic carbon, and sulfate aerosols, have been found to affect the Asian monsoon through direct and indirect aerosol radiative forcing. In this work, we use the coupled regional Weather Research and Forecasting model with Chemistry (WRF-Chem) to understand how aerosol changes from local emission sources could modulate the Asian monsoon precipitation through aerosol direct and indirect radiative effects. Our modeling results with the consideration of the local emissions show an improvement in simulated monsoon precipitation, when compared to reanalysis data and satellite observations. Aerosols generally induce a reduction in pre-monsoon and monsoon precipitation in East Asia. Over the Indian region, local anthropogenic emissions tend to reduce precipitation in the source regions while slightly increasing precipitation outside of the emission source regions. The increase in precipitation corresponds to a decrease in the cloud base level or lifting condensation level. Analysis of vertical cloud properties suggests that the increased cloud droplet number and prolonged cloud lifetime/reduced precipitation efficiency due to the local aerosol emissions are responsible for the precipitation reduction over East Asia. Aerosols from local emissions also play a very important role in the simulated surface temperature, radiation, and monsoon circulations.

Constraining direct aerosol radiative forcing using remote sensing and in-situ constraints

2020 ◽  
Author(s):  
Lucia Timea Deaconu ◽  
Duncan Watson-Parris ◽  
Philip Stier ◽  
Lindsay Lee
Keyword(s):  
Remote Sensing ◽  
Black Carbon ◽  
Optical Depth ◽  
Radiative Forcing ◽  
Removal Rates ◽  
Aerosol Radiative Forcing ◽  
Aerosol Absorption ◽  
Direct Radiative Forcing ◽  
Aerosol Radiative

<p>Absorbing aerosols affect the climate system (radiative forcing, cloud formation, precipitation and more) by strongly absorbing solar radiation, particularly at ultraviolet and visible wavelengths. The environmental impacts of an absorbing aerosol layer are influenced by its single scattering albedo (SSA), the albedo of the underlying surface, and also by the atmospheric residence time and column concentration of the aerosols.</p><p>Black-carbon (BC), the collective term used for strongly absorbing, carbonaceous aerosols, emitted by incomplete combustion of fossil fuel, biofuel and biomass, is a significant contributor to atmospheric absorption and probably a main-driver in inter-model differences and large uncertainties in estimating the aerosol radiative forcing due to aerosol-radiation interaction (RFari). Estimates of BC direct radiative forcing suggest a positive effect of +0.71 Wm<sup>-2</sup> (Bond and Bergstrom (2006)) with large uncertainties [+0.08, +1.27] Wm<sup>-2</sup>. These uncertainties result from poor estimates of BC atmospheric burden (emissions and removal rates) and its radiative properties. The uncertainty in the burden is due to the uncertainty in emissions (7.5 [2, 29] Tg yr<sup>-1</sup>) and lifetime (removal rates). In comparison with the available observations, global climate models (GCMs) tend to under-predict absorption near source (e.g. at AERONET stations), and over-predict concentrations in remote regions (e.g. as measured by aircraft campaigns). This may be due to GCM’s weak emissions at the source, but longer lifetime of aerosols in the atmosphere.</p><p>This study aims to address the parametric uncertainty of GCMs and constrain the direct radiative forcing using a perturbed parameter ensemble (PPE) and a collection of observations, from remote sensing to in-situ measurements. Total atmospheric aerosol extinction is quantified using satellite observations that provide aerosol optical depth (AOD), while the SSA is constrained by the use of high-temporal resolution aerosol absorption optical depth (AAOD) measured with AERONET sun-photometers (for near-source columnar information of aerosol absorption) and airborne black-carbon in-situ measurements collected and synthesised in the Global Aerosol Synthesis and Science Project (GASSP) (for properties of long-range transported aerosols). Measurements from the airborne campaigns ATOM and HIPPO are valuable for constraining aerosol absorption in remote areas, while CLARIFY and ORACLES, that were employed over Southeast Atlantic, are considered in our study for near source observations of biomass burning aerosols transported over the bright surface of stratocumulus clouds.</p><p>Using the PPE to explore the uncertainties in the aerosol absorption as well as the dominant emission and removal processes, and by comparing with a variety of observations we have confidence to better constrain the aerosol direct radiative forcing.</p>

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.

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