Cloudy sky contributions to the direct aerosol effect

Abstract. The radiative forcing of the aerosol-radiation interaction can be decomposed into clear sky and cloudy sky portions. Two sets of multi-model simulations within AeroCom, combined with observational methods, and the time evolution of aerosol emissions over the industrial era show that the contribution from cloudy sky regions is likely weak. A mean of the simulations considered is 0.01 ± 0.1 W m−2. Multivariate data analysis of results from AeroCom Phase II shows that many factors influence the strength of the cloudy sky contribution to the forcing of the aerosol-radiation interaction. Overall, single scattering albedo of anthropogenic aerosols and the interaction of aerosols with the shortwave cloud radiative effects are found to be important factors. A more dedicated focus on the contribution from the cloud free and cloud covered sky fraction respectively to the aerosol-radiation interaction will benefit the quantification of the radiative forcing and its uncertainty range.

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Cloudy-sky contributions to the direct aerosol effect

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-8855-2020 ◽

2020 ◽

Vol 20 (14) ◽

pp. 8855-8865 ◽

Cited By ~ 1

Author(s):

Gunnar Myhre ◽

Bjørn H. Samset ◽

Christian W. Mohr ◽

Kari Alterskjær ◽

Yves Balkanski ◽

...

Keyword(s):

Radiative Forcing ◽

Single Scattering ◽

Short Wave ◽

Anthropogenic Aerosols ◽

Uncertainty Range ◽

Clear Sky ◽

Aerosol Effect ◽

Analysis Of Results ◽

Cloud Radiative Effects ◽

Aerosol Emissions

Abstract. The radiative forcing of the aerosol–radiation interaction can be decomposed into clear-sky and cloudy-sky portions. Two sets of multi-model simulations within Aerosol Comparisons between Observations and Models (AeroCom), combined with observational methods, and the time evolution of aerosol emissions over the industrial era show that the contribution from cloudy-sky regions is likely weak. A mean of the simulations considered is 0.01±0.1 W m−2. Multivariate data analysis of results from AeroCom Phase II shows that many factors influence the strength of the cloudy-sky contribution to the forcing of the aerosol–radiation interaction. Overall, single-scattering albedo of anthropogenic aerosols and the interaction of aerosols with the short-wave cloud radiative effects are found to be important factors. A more dedicated focus on the contribution from the cloud-free and cloud-covered sky fraction, respectively, to the aerosol–radiation interaction will benefit the quantification of the radiative forcing and its uncertainty range.

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Effective radiative forcing in the aerosol–climate model CAM5.3-MARC-ARG

10.5194/acp-2018-118 ◽

2018 ◽

Cited By ~ 1

Author(s):

Benjamin S. Grandey ◽

Daniel Rothenberg ◽

Alexander Avramov ◽

Qinjian Jin ◽

Hsiang-He Lee ◽

...

Keyword(s):

Radiative Forcing ◽

Climate Model ◽

Regional Distribution ◽

Radiative Effect ◽

Mixing State ◽

Anthropogenic Aerosols ◽

Effective Radiative Forcing ◽

Aerosol Module ◽

Aerosol Emissions ◽

Global Mean

Abstract. We quantify the effective radiative forcing (ERF) of anthropogenic aerosols modelled by the aerosol–climate model CAM5.3-MARC-ARG. CAM5.3-MARC-ARG is a new configuration of the Community Atmosphere Model version 5.3 (CAM5.3) in which the default aerosol module has been replaced by the two-Moment, Multi-Modal, Mixing-state-resolving Aerosol model for Research of Climate (MARC). CAM5.3-MARC-ARG uses the default ARG aerosol activation scheme, consistent with the default configuration of CAM5.3. We compute differences between simulations using year-1850 aerosol emissions and simulations using year-2000 aerosol emissions in order to assess the radiative effects of anthropogenic aerosols. We compare the aerosol column burdens, cloud properties, and radiative effects produced by CAM5.3-MARC-ARG with those produced by the default configuration of CAM5.3, which uses the modal aerosol module with three log-normal modes (MAM3). Compared with MAM3, we find that MARC produces stronger cooling via the direct radiative effect, stronger cooling via the surface albedo radiative effect, and stronger warming via the cloud longwave radiative effect. The global mean cloud shortwave radiative effect is similar between MARC and MAM3, although the regional distributions differ. Overall, MARC produces a global mean net ERF of −1.75 ± 0.04 W m−2, which is stronger than the global mean net ERF of −1.57 ± 0.04 W m−2 produced by MAM3. The regional distribution of ERF also differs between MARC and MAM3, largely due to differences in the regional distribution of the cloud shortwave radiative effect. We conclude that the specific representation of aerosols in global climate models, including aerosol mixing state, has important implications for climate modelling.

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Direct Aerosol Radiative Forcing Uncertainty Based on a Radiative Perturbation Analysis

Journal of Climate ◽

10.1175/2010jcli3543.1 ◽

2010 ◽

Vol 23 (19) ◽

pp. 5288-5293 ◽

Cited By ~ 81

Author(s):

Norman G. Loeb ◽

Wenying Su

Keyword(s):

Radiative Forcing ◽

Single Scattering ◽

Single Scattering Albedo ◽

Aerosol Radiative Forcing ◽

Clear Sky ◽

Radiative Perturbation ◽

Sky Conditions ◽

Global Mean ◽

Aerosol Properties ◽

Aerosol Radiative

Abstract To provide a lower bound for the uncertainty in measurement-based clear- and all-sky direct aerosol radiative forcing (DARF), a radiative perturbation analysis is performed for the ideal case in which the perturbations in global mean aerosol properties are given by published values of systematic uncertainty in Aerosol Robotic Network (AERONET) aerosol measurements. DARF calculations for base-state climatological cloud and aerosol properties over ocean and land are performed, and then repeated after perturbing individual aerosol optical properties (aerosol optical depth, single-scattering albedo, asymmetry parameter, scale height, and anthropogenic fraction) from their base values, keeping all other parameters fixed. The total DARF uncertainty from all aerosol parameters combined is 0.5–1.0 W m−2, a factor of 2–4 greater than the value cited in the Intergovernmental Panel on Climate Change’s (IPCC’s) Fourth Assessment Report. Most of the total DARF uncertainty in this analysis is associated with single-scattering albedo uncertainty. Owing to the greater sensitivity to single-scattering albedo in cloudy columns, DARF uncertainty in all-sky conditions is greater than in clear-sky conditions, even though the global mean clear-sky DARF is more than twice as large as the all-sky DARF.

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Reply to “Comment on ‘Rethinking the Lower Bound on Aerosol Radiative Forcing’”

Journal of Climate ◽

10.1175/jcli-d-17-0034.1 ◽

2017 ◽

Vol 30 (16) ◽

pp. 6585-6589 ◽

Cited By ~ 4

Author(s):

Bjorn Stevens ◽

Stephanie Fiedler

Keyword(s):

Twentieth Century ◽

Lower Bound ◽

Radiative Forcing ◽

Climate Models ◽

Anthropogenic Aerosols ◽

Anthropogenic Aerosol ◽

Aerosol Radiative Forcing ◽

Clear Sky ◽

The North ◽

Aerosol Forcing

Kretzschmar et al., in a comment in 2017, use the spread in the output of aerosol–climate models to argue that the models refute the hypothesis (presented in a paper by Stevens in 2015) that for the mid-twentieth-century warming to be consistent with observations, then the present-day aerosol forcing, [Formula: see text] must be less negative than −1 W m−2. The main point of contention is the nature of the relationship between global SO2 emissions and [Formula: see text] In contrast to the concave (log-linear) relationship used by Stevens and in earlier studies, whereby [Formula: see text] becomes progressively less sensitive to SO2 emissions, some models suggest a convex relationship, which would imply a less negative lower bound. The model that best exemplifies this difference, and that is most clearly in conflict with the hypothesis of Stevens, does so because of an implausible aerosol response to the initial rise in anthropogenic aerosol precursor emissions in East and South Asia—already in 1975 this model’s clear-sky reflectance from anthropogenic aerosol over the North Pacific exceeds present-day estimates of the clear-sky reflectance by the total aerosol. The authors perform experiments using a new (observationally constrained) climatology of anthropogenic aerosols to further show that the effects of changing patterns of aerosol and aerosol precursor emissions during the late twentieth century have, for the same global emissions, relatively little effect on [Formula: see text] These findings suggest that the behavior Kretzschmar et al. identify as being in conflict with the lower bound in Stevens arises from an implausible relationship between SO2 emissions and [Formula: see text] and thus provides little basis for revising this lower bound.

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

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-6-5095-2006 ◽

2006 ◽

Vol 6 (3) ◽

pp. 5095-5136 ◽

Cited By ~ 11

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.

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Radiative forcing of the direct aerosol effect from AeroCom Phase II simulations

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-12-22355-2012 ◽

2012 ◽

Vol 12 (8) ◽

pp. 22355-22413 ◽

Cited By ~ 18

Author(s):

G. Myhre ◽

B. H. Samset ◽

M. Schulz ◽

Y. Balkanski ◽

S. Bauer ◽

...

Keyword(s):

Phase Ii ◽

Radiative Forcing ◽

Fossil Fuel ◽

Organic Aerosols ◽

Anthropogenic Aerosols ◽

Aerosol Effect ◽

Time Period ◽

Aerosol Distribution ◽

The Mean ◽

The Individual

Abstract. We report on the AeroCom Phase II direct aerosol effect (DAE) experiment where 15 detailed global aerosol models have been used to simulate the changes in the aerosol distribution over the industrial era. All 15 models have estimated the radiative forcing (RF) of the anthropogenic DAE, and have taken into account anthropogenic sulphate, black carbon (BC) and organic aerosols (OA) from fossil fuel, biofuel, and biomass burning emissions. In addition several models have simulated the DAE of anthropogenic nitrate and anthropogenic influenced secondary organic aerosols (SOA). The model simulated all-sky RF of the DAE from total anthropogenic aerosols has a range from −0.58 to −0.02 W m−2, with a mean of −0.30 W m−2 for the 15 models. Several models did not include nitrate or SOA and modifying the estimate by accounting for this with information from the other AeroCom models reduces the range and slightly strengthens the mean. Modifying the model estimates for missing aerosol components and for the time period 1750 to 2010 results in a mean RF for the DAE of −0.39 W m−2. Compared to AeroCom Phase I (Schulz et al., 2006) we find very similar spreads in both total DAE and aerosol component RF. However, the RF of the total DAE is stronger negative and RF from BC from fossil fuel and biofuel emissions are stronger positive in the present study than in the previous AeroCom study. We find a tendency for models having a strong (positive) BC RF to also have strong (negative) sulphate or OA RF. This relationship leads to smaller uncertainty in the total RF of the DAE compared to the RF of the sum of the individual aerosol components. The spread in results for the individual aerosol components is substantial, and can be divided into diversities in burden, mass extinction coefficient (MEC), and normalized RF with respect to AOD. We find that these three factors give similar contributions to the spread in results.

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Surface Aerosol Properties Studied Using a Near-Horizontal Lidar

Atmosphere ◽

10.3390/atmos11010036 ◽

2019 ◽

Vol 11 (1) ◽

pp. 36 ◽

Cited By ~ 2

Author(s):

Prane Mariel Ong ◽

Nofel Lagrosas ◽

Tatsuo Shiina ◽

Hiroaki Kuze

Keyword(s):

Radiative Forcing ◽

Transition Period ◽

Single Scattering ◽

Lidar Data ◽

Aerosol Extinction ◽

Near Surface ◽

Ambient Relative Humidity ◽

Aerosol Effect ◽

Aerosol Extinction Coefficient ◽

Aerosol Properties

Studying near-surface aerosol properties is of importance for a better assessment of the aerosol effect on radiative forcing. We employ the data from a near-horizontal lidar to investigate the diurnal behavior of aerosol extinction and single scattering albedo (SSA) at 349 nm. The response of these parameters to ambient relative humidity (RH) is examined for the data from a one-month campaign conducted in Chiba, Japan, during November 2017, a transition period from fall to winter. The Klett method and adaptive slope method are used in deriving the aerosol extinction coefficient from the lidar data, while the SSA values are retrieved using an aethalometer. Also, a visibility-meter is used to examine the aerosol loading inside the atmospheric boundary layer. It is found that the aerosol growth during the deliquescence phase is more readily observed than the contraction in the efflorescence phase. The decrease of SSA before the deliquescence RH is found for approximately 46% of the deliquescence cases, presumably representing the particle shrinkage of soot particles.

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Subgrid-scale variability of clear-sky relative humidity and forcing by aerosol-radiation interactions in an atmosphere model

10.5194/acp-2017-839 ◽

2017 ◽

Author(s):

Paul Petersik ◽

Marc Salzmann ◽

Jan Kretzschmar ◽

Ribu Cherian ◽

Daniel Mewes ◽

...

Keyword(s):

Relative Humidity ◽

Radiative Forcing ◽

Cloud Cover ◽

Specific Humidity ◽

Subgrid Scale ◽

Hygroscopic Growth ◽

Anthropogenic Aerosols ◽

Clear Sky ◽

Fractional Cloud ◽

Atmosphere Model

Abstract. Atmosphere models with resolutions of several tens of kilometres take subgrid-scale variability of the total specific humidity qt into account by using a uniform probability density function (PDF) to predict fractional cloud cover. However, usually only mean relative humidity RH or mean clear-sky relative humidity RHcls is used to compute hygroscopic growth of soluble aerosol particles. In this study, a stochastic parameterization of subgrid-scale variability of RHcls is applied. For this, we sample the subsaturated part of the uniform RH-PDF from the cloud cover scheme for application in association with the hygroscopic growth parameterization in the ECHAM6-HAM2 atmosphere model. Due to the non-linear dependence of the hygroscopic growth on RH, this causes an increase in aerosol hygroscopic growth. Aerosol optical depth (AOD) increases by a global mean of 0.009 (∼ 7.8 % in comparison to the control run). Especially over the tropics AOD is enhanced with a mean of about 0.013. The ability of the model to simulate AOD is slightly improved with respect to satellite data from MODIS-Aqua. Due to the increase in AOD, net top of the atmosphere clear-sky solar radiation decreases by −0.22 W m−2 (∼ −0.08 %). Finally, the effective radiative forcing due to aerosol-radiation interactions under clear-sky conditions (ERFaricls) changes from −0.29 W m−2 to −0.45 W m−2 by about 57 %. The reason for this very disproportionate effect is that anthropogenic aerosols are disproportionally hygroscopic.

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Radiative forcing of the direct aerosol effect from AeroCom Phase II simulations

Atmospheric Chemistry and Physics ◽

10.5194/acp-13-1853-2013 ◽

2013 ◽

Vol 13 (4) ◽

pp. 1853-1877 ◽

Cited By ~ 485

Author(s):

G. Myhre ◽

B. H. Samset ◽

M. Schulz ◽

Y. Balkanski ◽

S. Bauer ◽

...

Keyword(s):

Phase Ii ◽

Radiative Forcing ◽

Fossil Fuel ◽

Organic Aerosols ◽

Anthropogenic Aerosols ◽

Aerosol Effect ◽

Time Period ◽

Aerosol Distribution ◽

The Mean ◽

The Individual

Abstract. We report on the AeroCom Phase II direct aerosol effect (DAE) experiment where 16 detailed global aerosol models have been used to simulate the changes in the aerosol distribution over the industrial era. All 16 models have estimated the radiative forcing (RF) of the anthropogenic DAE, and have taken into account anthropogenic sulphate, black carbon (BC) and organic aerosols (OA) from fossil fuel, biofuel, and biomass burning emissions. In addition several models have simulated the DAE of anthropogenic nitrate and anthropogenic influenced secondary organic aerosols (SOA). The model simulated all-sky RF of the DAE from total anthropogenic aerosols has a range from −0.58 to −0.02 Wm−2, with a mean of −0.27 Wm−2 for the 16 models. Several models did not include nitrate or SOA and modifying the estimate by accounting for this with information from the other AeroCom models reduces the range and slightly strengthens the mean. Modifying the model estimates for missing aerosol components and for the time period 1750 to 2010 results in a mean RF for the DAE of −0.35 Wm−2. Compared to AeroCom Phase I (Schulz et al., 2006) we find very similar spreads in both total DAE and aerosol component RF. However, the RF of the total DAE is stronger negative and RF from BC from fossil fuel and biofuel emissions are stronger positive in the present study than in the previous AeroCom study. We find a tendency for models having a strong (positive) BC RF to also have strong (negative) sulphate or OA RF. This relationship leads to smaller uncertainty in the total RF of the DAE compared to the RF of the sum of the individual aerosol components. The spread in results for the individual aerosol components is substantial, and can be divided into diversities in burden, mass extinction coefficient (MEC), and normalized RF with respect to AOD. We find that these three factors give similar contributions to the spread in results.

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Effective radiative forcing of anthropogenic aerosols in E3SMv1: historical changes, causality, decomposition, and parameterization sensitivities

10.5194/acp-2021-1087 ◽

2022 ◽

Author(s):

Kai Zhang ◽

Wentao Zhang ◽

Hui Wan ◽

Philip J. Rasch ◽

Steven J. Ghan ◽

...

Keyword(s):

Optical Depth ◽

Radiative Forcing ◽

Cloud Droplet ◽

Anthropogenic Aerosols ◽

Anthropogenic Aerosol ◽

Ice Cloud ◽

Cloud Properties ◽

Aerosol Effect ◽

Effective Radiative Forcing ◽

Depth Increase

Abstract. The effective radiative forcing of anthropogenic aerosols (ERFaer) is an important measure of the anthropogenic aerosol effects simulated by a global climate model. Here we analyze ERFaer simulated by the E3SMv1 atmosphere model using both century-long free-running atmosphere-land simulations and short nudged simulations. We relate the simulated ERFaer to characteristics of the aerosol composition and optical properties, and evaluate the relationships between key aerosol and cloud properties. In terms of historical changes from the year 1870 to 2014, our results show that the global mean anthropogenic aerosol burden and optical depth increase during the simulation period as expected, but the regional averages show large differences in the temporal evolution. The largest regional differences are found in the emission-induced evolution of the burden and optical depth of the sulfate aerosol: a strong decreasing trend is seen in the Northern Hemisphere high-latitude region after around 1970, while a continued increase is simulated in the tropics. Consequently, although the global mean anthropogenic aerosol burden and optical depth increase from 1870 to 2014, the ERFaer magnitude does not increase after around year 1970. The relationships between key aerosol and cloud properties (relative changes between preindustrial and present-day conditions) also show evident changes after 1970, diverging from the linear relationships exhibited for the period from 1870 to 2014. The ERFaer in E3SMv1 is relatively large compared to the recently published multi-model estimates; the primary reason is the large indirect aerosol effect (i.e., through aerosol-cloud interactions). Compared to other models, E3SMv1 features a stronger sensitivity of the cloud droplet effective radius to changes in the cloud droplet number concentration. Large sensitivity is also seen in the liquid cloud optical depth, which is determined by changes in both the effective radius and liquid water path. Aerosol-induced changes in liquid and ice cloud properties in E3SMv1 are found to have a strong correlation, as the evolution of anthropogenic sulfate aerosols affects both the liquid cloud formation and the homogeneous ice nucleation in cirrus clouds. The ERFaer estimates in E3SMv1 for the shortwave and longwave components are sensitive to the parameterization changes in both liquid and ice cloud processes. When the parameterization of ice cloud processes is modified, the top-of-atmosphere forcing changes in the shortwave and longwave components largely offset each other, so the net effect is negligible. This suggests that, to reduce the magnitude of the net ERFaer, it would be more effective to reduce the anthropogenic aerosol effect through liquid or mixed-phase clouds.

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