New approaches to quantifying aerosol influence on the cloud radiative effect

The topic of cloud radiative forcing associated with the atmospheric aerosol has been the focus of intense scrutiny for decades. The enormity of the problem is reflected in the need to understand aspects such as aerosol composition, optical properties, cloud condensation, and ice nucleation potential, along with the global distribution of these properties, controlled by emissions, transport, transformation, and sinks. Equally daunting is that clouds themselves are complex, turbulent, microphysical entities and, by their very nature, ephemeral and hard to predict. Atmospheric general circulation models represent aerosol−cloud interactions at ever-increasing levels of detail, but these models lack the resolution to represent clouds and aerosol−cloud interactions adequately. There is a dearth of observational constraints on aerosol−cloud interactions. We develop a conceptual approach to systematically constrain the aerosol−cloud radiative effect in shallow clouds through a combination of routine process modeling and satellite and surface-based shortwave radiation measurements. We heed the call to merge Darwinian and Newtonian strategies by balancing microphysical detail with scaling and emergent properties of the aerosol−cloud radiation system.

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Snow-induced buffering in aerosol–cloud interactions

10.5194/acp-2020-232 ◽

2020 ◽

Author(s):

Takuro Michibata ◽

Kentaroh Suzuki ◽

Toshihiko Takemura

Keyword(s):

Radiative Forcing ◽

General Circulation ◽

State Of The Art ◽

General Circulation Models ◽

Regional Pattern ◽

Cloud Droplets ◽

Microphysical Process ◽

Aerosol Cloud ◽

Effective Radiative Forcing ◽

Aerosol Cloud Interactions

Abstract. Complex aerosol–cloud–precipitation interactions lead to large differences in estimates of aerosol impacts on climate among general circulation models (GCMs) and satellite retrievals. Typically, precipitating hydrometeors are treated diagnostically in most GCMs, and their radiative effects are ignored. Here, we quantify how the treatment of precipitation influences the simulated effective radiative forcing due to aerosol–cloud interactions (ERFaci) using a state-of-the-art GCM with a two-moment prognostic precipitation scheme that incorporates the radiative effect of precipitating particles, and investigate how microphysical process representations are related to macroscopic climate effects. Prognostic precipitation substantially weakens the magnitude of ERFaci (by approximately 75 %) compared with the traditional diagnostic scheme, and this is the result of the increased longwave (warming) and weakened shortwave (cooling) components of ERFaci. The former is attributed to additional adjustment processes induced by falling snow, and the latter stems largely from riming of snow by collection of cloud droplets. The significant reduction in ERFaci does not occur without prognostic snow, which contributes mainly by buffering the cloud response to aerosol perturbations through depleting cloud water via collection. Prognostic precipitation also alters the regional pattern of ERFaci, particularly over northern mid-latitudes where snow is abundant. The treatment of precipitation is thus a highly influential controlling factor of ERFaci, contributing more than other uncertain tunable processes related to aerosol–cloud–precipitation interactions. This change in ERFaci caused by the treatment of precipitation is large enough to explain the existing difference in ERFaci between GCMs and observations.

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A global satellite view of aerosol cloud interactions

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-4-6823-2004 ◽

2004 ◽

Vol 4 (5) ◽

pp. 6823-6836 ◽

Cited By ~ 3

Author(s):

C. Luo

Keyword(s):

North Africa ◽

North Atlantic ◽

Radiative Forcing ◽

General Circulation ◽

Large Scale ◽

Regional Scale ◽

Cloud Amount ◽

General Circulation Models ◽

Aerosol Cloud ◽

Aerosol Cloud Interactions

Abstract. Long-term and large-scale correlations between Advanced Very High-Resolution Radiometer (AVHRR) aerosol optical depth and International Satellite Cloud Climatology Project (ISCCP) monthly cloud amount data show significant regional scale relationships between cloud amount and aerosols, consistent with aerosol-cloud interactions. Positive correlations between aerosols and cloud amount are associated with North American and Asian aerosols in the North Atlantic and Pacific storm tracks, and mineral aerosols in the tropical North Atlantic. Negative correlations are seen near biomass burning regions of North Africa and Indonesia, as well as south of the main mineral aerosol source of North Africa. These results suggest that there are relationships between aerosols and clouds in the observations that can be used by general circulation models to verify the correct forcing mechanisms for both direct and indirect radiative forcing by clouds.

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Improving our fundamental understanding of the role of aerosol−cloud interactions in the climate system

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1514043113 ◽

2016 ◽

Vol 113 (21) ◽

pp. 5781-5790 ◽

Cited By ~ 199

Author(s):

John H. Seinfeld ◽

Christopher Bretherton ◽

Kenneth S. Carslaw ◽

Hugh Coe ◽

Paul J. DeMott ◽

...

Keyword(s):

Remote Sensing ◽

Radiative Forcing ◽

General Circulation ◽

Climate Models ◽

Large Range ◽

General Circulation Models ◽

Radiative Properties ◽

Aerosol Cloud ◽

Aerosol Cloud Interactions

The effect of an increase in atmospheric aerosol concentrations on the distribution and radiative properties of Earth’s clouds is the most uncertain component of the overall global radiative forcing from preindustrial time. General circulation models (GCMs) are the tool for predicting future climate, but the treatment of aerosols, clouds, and aerosol−cloud radiative effects carries large uncertainties that directly affect GCM predictions, such as climate sensitivity. Predictions are hampered by the large range of scales of interaction between various components that need to be captured. Observation systems (remote sensing, in situ) are increasingly being used to constrain predictions, but significant challenges exist, to some extent because of the large range of scales and the fact that the various measuring systems tend to address different scales. Fine-scale models represent clouds, aerosols, and aerosol−cloud interactions with high fidelity but do not include interactions with the larger scale and are therefore limited from a climatic point of view. We suggest strategies for improving estimates of aerosol−cloud relationships in climate models, for new remote sensing and in situ measurements, and for quantifying and reducing model uncertainty.

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Apportionment of the present-day forcing by methane using UKESM1: The role of chemistry-aerosol-cloud interactions

10.5194/egusphere-egu21-16375 ◽

2021 ◽

Author(s):

Fiona O'Connor ◽

Omar Jamil ◽

Timothy Andrews ◽

Ben Johnson ◽

Jane Mulcahy ◽

...

Keyword(s):

Indirect Effects ◽

Radiative Forcing ◽

Cloud Droplet ◽

Aerosol Size Distribution ◽

Radiative Effect ◽

Liquid Water Path ◽

Model Estimate ◽

Aerosol Cloud ◽

Cloud Radiative Effect ◽

Aerosol Cloud Interactions

The pre-industrial (PI; Year 1850) to present-day (PD; Year 2014) increase in methane concentration leads to a global mean effective radiative forcing (ERF) of 0.97 &#177; 0.04 W m-2 in the UK&#8217;s Earth System Model, UKESM1. In comparison with the multi-model estimate of 0.75 &#177; 0.10 W m-2 from the Aerosol and Chemistry Model Intercomparison Project (AerChemMIP), UKESM1 has the highest methane ERF and lies outside the 1-sigma range. This is, in part, due to UKESM1 including interactive chemistry and positive indirect effects, such as methane-driven changes in tropospheric ozone. However, UKESM1 is the only model within AerChemMIP whose contribution to the methane ERF from tropospheric adjustments is positive &#8211; this is largely driven by the strong positive cloud adjustment in UKESM1, in contrast to other models. In this work, we apportion the total methane ERF between direct and indirect effects (including adjustments) and provide a process-based understanding of what is driving the positive cloud adjustment in UKESM1.Using additional UKESM1 paired simulations, we apportion the total methane ERF between its direct methane contribution and indirect contributions from ozone, water vapour, and aerosols. This approach offers the advantage that linearity is not assumed and it distinguishes between cloud effects that are dynamically-driven via changes in temperature and those that are aerosol-mediated. By analysing the chemistry-aerosol budgets and the cloud responses, we find that the PI to PD increase in methane leads to an indirect positive aerosol ERF of up to 0.3 &#177; 0.06 W m-2, with a near-zero contribution from the instantaneous radiative forcing from aerosol-radiation interactions. Methane-driven changes in oxidants alter the relative contributions of the different sulphur dioxide oxidation pathways, causing a change in new particle formation rates and a shift in the aerosol size distribution towards fewer but larger particles. There is a resulting decrease in cloud droplet number concentration, an increase in cloud droplet effective radius, and a decrease in liquid water path in marine stratocumulus regions from aerosol-cloud interactions (mainly through the cloud lifetime effect). There is a subsequent change in the cloud radiative effect, with the positive change in the shortwave dominating over the negative change in the longwave. However, when aerosol-cloud interactions are disabled, the change in the cloud radiative effect is negative and is dominated by the reduction of cirrus clouds in the tropics, thus making UKESM1 more consistent with the other AerChemMIP models.These results can explain some of the diversity in multi-model estimates of methane forcing and highlight the importance of chemistry-aerosol-cloud interactions when quantifying climate forcing by reactive greenhouse gases.

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Snow-induced buffering in aerosol–cloud interactions

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-13771-2020 ◽

2020 ◽

Vol 20 (22) ◽

pp. 13771-13780

Author(s):

Takuro Michibata ◽

Kentaroh Suzuki ◽

Toshihiko Takemura

Keyword(s):

Radiative Forcing ◽

General Circulation ◽

State Of The Art ◽

General Circulation Models ◽

Regional Pattern ◽

Cloud Droplets ◽

Microphysical Process ◽

Aerosol Cloud ◽

Effective Radiative Forcing ◽

Aerosol Cloud Interactions

Abstract. Complex aerosol–cloud–precipitation interactions lead to large differences in estimates of aerosol impacts on climate among general circulation models (GCMs) and satellite retrievals. Typically, precipitating hydrometeors are treated diagnostically in most GCMs, and their radiative effects are ignored. Here, we quantify how the treatment of precipitation influences the simulated effective radiative forcing due to aerosol–cloud interactions (ERFaci) using a state-of-the-art GCM with a two-moment prognostic precipitation scheme that incorporates the radiative effect of precipitating particles, and we investigate how microphysical process representations are related to macroscopic climate effects. Prognostic precipitation substantially weakens the magnitude of ERFaci (by approximately 54 %) compared with the traditional diagnostic scheme, and this is the result of the increased longwave (warming) and weakened shortwave (cooling) components of ERFaci. The former is attributed to additional adjustment processes induced by falling snow, and the latter stems largely from riming of snow by collection of cloud droplets. The significant reduction in ERFaci does not occur without prognostic snow, which contributes mainly by buffering the cloud response to aerosol perturbations through depleting cloud water via collection. Prognostic precipitation also alters the regional pattern of ERFaci, particularly over northern midlatitudes where snow is abundant. The treatment of precipitation is thus a highly influential controlling factor of ERFaci, contributing more than other uncertain “tunable” processes related to aerosol–cloud–precipitation interactions. This change in ERFaci caused by the treatment of precipitation is large enough to explain the existing difference in ERFaci between GCMs and observations.

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Machine learning uncovers aerosol size information from chemistry and meteorology to quantify potential cloud-forming particles

10.21203/rs.3.rs-244416/v1 ◽

2021 ◽

Author(s):

Arshad Nair ◽

Fangqun Yu ◽

Pedro Campuzano Jost ◽

Paul DeMott ◽

Ezra Levin ◽

...

Keyword(s):

Climate Change ◽

Machine Learning ◽

Radiative Forcing ◽

Climate Models ◽

Cloud Condensation Nuclei ◽

Global Climate Models ◽

Aerosol Composition ◽

Airborne Measurements ◽

Aerosol Cloud ◽

Aerosol Cloud Interactions

Abstract Cloud condensation nuclei (CCN) are mediators of aerosol–cloud interactions, which contribute to the largest uncertainty in climate change prediction. Here, we present a machine learning/artificial intelligence model that quantifies CCN from variables of aerosol composition, atmospheric trace gases, and meteorology. Comprehensive multi-campaign airborne measurements, covering varied physicochemical regimes in the troposphere, confirm the validity of and help probe the inner workings of this machine learning model: revealing for the first time that different ranges of atmospheric aerosol composition and mass correspond to distinct aerosol number size distributions. Machine learning extracts this information, important for accurate quantification of CCN, additionally from both chemistry and meteorology. This can provide a physicochemically explainable, computationally efficient, robust machine learning pathway in global climate models that only resolve aerosol composition; potentially mitigating the uncertainty of effective radiative forcing due to aerosol–cloud interactions (ERFaci) and improving confidence in assessment of anthropogenic contributions and climate change projections.

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A long-term study of aerosol–cloud interactions and their radiative effect at a mid latitude continental site using ground-based measurements

10.5194/acp-2016-271 ◽

2016 ◽

Author(s):

Elisa T. Sena ◽

Allison McComiskey ◽

Graham Feingold

Keyword(s):

Great Plains ◽

Climate Models ◽

Cloud Droplet ◽

Droplet Size Distribution ◽

Radiative Effect ◽

Aerosol Cloud ◽

Long Term Study ◽

Cloud Radiative Effect ◽

Aerosol Cloud Interactions

Abstract. Empirical estimates of the microphysical response of cloud droplet size distribution to aerosol perturbations are commonly used to constrain aerosol–cloud interactions in climate models. Instead of empirical microphysical estimates, here macroscopic variables are analyzed to address the influences of aerosol particles and meteorological descriptors on instantaneous cloud albedo and radiative effect of shallow liquid water clouds. Long-term ground-based measurements from the Atmospheric Radiation Measurement (ARM) Program over the Southern Great Plains are used. A broad statistical analysis was performed on 14-years of coincident measurements of low clouds, aerosol and meteorological properties. Two cases representing conflicting results regarding the relationship between the aerosol and the cloud radiative effect were selected and studied in greater detail. Microphysical estimates are shown to be very uncertain and to depend strongly on the methodology, retrieval technique, and averaging scale. For this continental site, the results indicate that the influence of aerosol on shallow cloud radiative effect and albedo is weak and that macroscopic cloud properties and dynamics play a much larger role in determining the instantaneous cloud radiative effect compared to microphysical effects.

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Global and regional modeling of clouds and aerosols in the marine boundary layer during VOCALS: the VOCA intercomparison

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-153-2015 ◽

2015 ◽

Vol 15 (1) ◽

pp. 153-172 ◽

Cited By ~ 21

Author(s):

M. C. Wyant ◽

C. S. Bretherton ◽

R. Wood ◽

G. R. Carmichael ◽

A. Clarke ◽

...

Keyword(s):

Boundary Layer ◽

General Circulation ◽

Marine Boundary Layer ◽

Quantitative Estimation ◽

Cloud Condensation Nuclei ◽

Cloud Droplet ◽

General Circulation Models ◽

Free Troposphere ◽

Aerosol Cloud ◽

Aerosol Cloud Interactions

Abstract. A diverse collection of models are used to simulate the marine boundary layer in the southeast Pacific region during the period of the October–November 2008 VOCALS REx (VAMOS Ocean Cloud Atmosphere Land Study Regional Experiment) field campaign. Regional models simulate the period continuously in boundary-forced free-running mode, while global forecast models and GCMs (general circulation models) are run in forecast mode. The models are compared to extensive observations along a line at 20° S extending westward from the South American coast. Most of the models simulate cloud and aerosol characteristics and gradients across the region that are recognizably similar to observations, despite the complex interaction of processes involved in the problem, many of which are parameterized or poorly resolved. Some models simulate the regional low cloud cover well, though many models underestimate MBL (marine boundary layer) depth near the coast. Most models qualitatively simulate the observed offshore gradients of SO2, sulfate aerosol, CCN (cloud condensation nuclei) concentration in the MBL as well as differences in concentration between the MBL and the free troposphere. Most models also qualitatively capture the decrease in cloud droplet number away from the coast. However, there are large quantitative intermodel differences in both means and gradients of these quantities. Many models are able to represent episodic offshore increases in cloud droplet number and aerosol concentrations associated with periods of offshore flow. Most models underestimate CCN (at 0.1% supersaturation) in the MBL and free troposphere. The GCMs also have difficulty simulating coastal gradients in CCN and cloud droplet number concentration near the coast. The overall performance of the models demonstrates their potential utility in simulating aerosol–cloud interactions in the MBL, though quantitative estimation of aerosol–cloud interactions and aerosol indirect effects of MBL clouds with these models remains uncertain.

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Impact of the aging process of black carbon aerosols on their spatial distribution, hygroscopicity, and radiative forcing in a global climate model

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-12-29801-2012 ◽

2012 ◽

Vol 12 (11) ◽

pp. 29801-29849 ◽

Cited By ~ 6

Author(s):

D. Goto ◽

N. Oshima ◽

T. Nakajima ◽

T. Takemura ◽

T. Ohara

Keyword(s):

Spatial Distribution ◽

Black Carbon ◽

Radiative Forcing ◽

General Circulation ◽

Aging Process ◽

Global Climate Model ◽

General Circulation Models ◽

Shortwave Radiation ◽

Conversion Rates ◽

Aerosol Modeling

Abstract. Black carbon (BC) absorbs shortwave radiation more strongly than any other type of aerosol, and an accurate simulation of the aging processes of BC-containing particle is required to properly predict aerosol radiative forcing (ARF) and climate change. However, BC aging processes have been simplified in general circulation models (GCMs) due to limited computational resources. In particular, differences in the representation of the mixing states of BC-containing particles between GCMs constitute one of main reasons for the uncertainty in ARF estimates. To understand an impact of the BC aging processes and the mixing state of BC on the spatial distribution of BC and ARF caused by BC (BC-ARF), we implemented three different methods of incorporating BC aging processes into a global aerosol transport model, SPRINTARS: (1) the "AGV" method, using variable conversion rates of BC aging based on a new type of parameterization depending on both BC amount and sulfuric acid; (2) the "AGF" method, using a constant conversion rate used worldwide in GCMs; and (3) the "ORIG" method, which is used in the original SPRINTARS. First, we found that these different methods produced different BC burden within 10% over industrial areas and 50% over remote oceans. Second, a ratio of water-insoluble BC to total BC (WIBC ratio) was very different among the three methods. Near the BC source region, for example, the WIBC ratios were estimated to be 80–90% (AGV and AGF) and 50–60% (ORIG). Third, although the BC aging process in GCMs had small impacts on the BC burden, they had a large impact on BC-ARF through a change in both the WIBC ratio and non-BC compounds coating on BC cores. As a result, possible differences in the treatment of the BC aging process between aerosol modeling studies can produce a difference of approximately 0.3 Wm−2 in the magnitude of BC-ARF, which is comparable to the uncertainty suggested by results from a global aerosol modeling intercomparison project, AeroCom. The surface aerosol forcing efficiencies normalized by aerosol optical thickness and by BC burden varied greatly with region in the AGV method, which allowed for the existence of internally mixed BC and sulfate, whereas these were not varied with region in the AGF method. These results suggest that the efficiencies of BC-ARF obtained by previous studies using the AGF method are significantly underestimated.

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Real-case simulations of aerosol-cloud interactions in ship tracks over the Bay of Biscay

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-14-26721-2014 ◽

2014 ◽

Vol 14 (19) ◽

pp. 26721-26764

Author(s):

A. Possner ◽

E. Zubler ◽

U. Lohmann ◽

C. Schär

Keyword(s):

General Circulation ◽

General Circulation Models ◽

Bay Of Biscay ◽

Test Bed ◽

Liquid Water Path ◽

Ship Emissions ◽

Regional Modelling ◽

Aerosol Cloud ◽

Ship Tracks ◽

Aerosol Cloud Interactions

Abstract. Ship tracks provide an ideal test bed for studying aerosol-cloud interactions (ACI) and for evaluating their representation in parameterisations. Regional modelling can be of particular use for this task, as this approach provides sufficient resolution to resolve the structure of the produced track including their meteorological environment whilst relying on the same formulations of parameterisations as many general circulation models. In this work we simulate a particular case of ship tracks embedded in an optically thin stratus cloud sheet which was observed by a polar orbiting satellite at 12:00 UTC on 26 January 2003 around the Bay of Biscay. The simulations which include moving ship emissions show that the model is indeed able to capture the structure of the track at a horizontal grid spacing of 2 km and to qualitatively capture the observed cloud response in all simulations performed. At least a doubling of the cloud optical thickness was simulated in all simulations together with an increase in cloud droplet number concentration (by about 50 cm−3) and decrease in effective radius (by about 5 μm). Furthermore the ship emissions lead to an increase in liquid water path in at least 25% of the track regions. We are confident in the model's ability to capture key processes of ship track formation. However, it was found that realistic ship emissions lead to unrealistic aerosol perturbations near the source regions within the simulated tracks due to grid-scale dilution and homogeneity. Combining the regional-modelling approach with comprehensive field studies could likely improve our understanding of the sensitivities and biases in ACI parameterisations, and could therefore help to constrain global ACI estimates, which strongly rely on these parameterisations.

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