The global aerosol-climate model ECHAM-HAM, version 2:  sensitivity to improvements in process representations

Abstract. This paper introduces and evaluates the second version of the global aerosol-climate model ECHAM-HAM. Major changes have been brought into the model, including new parameterizations for aerosol nucleation and water uptake, an explicit treatment of secondary organic aerosols, modified emission calculations for sea salt and mineral dust, the coupling of aerosol microphysics to a two-moment stratiform cloud microphysics scheme, and alternative wet scavenging parameterizations. These revisions extend the model's capability to represent details of the aerosol lifecycle and its interaction with climate. Nudged simulations of the year 2000 are carried out to compare the aerosol properties and global distribution in HAM1 and HAM2, and to evaluate them against various observations. Sensitivity experiments are performed to help identify the impact of each individual update in model formulation. Results indicate that from HAM1 to HAM2 there is a marked weakening of aerosol water uptake in the lower troposphere, reducing the total aerosol water burden from 75 Tg to 51 Tg. The main reason is the newly introduced κ-Köhler-theory-based water uptake scheme uses a lower value for the maximum relative humidity cutoff. Particulate organic matter loading in HAM2 is considerably higher in the upper troposphere, because the explicit treatment of secondary organic aerosols allows highly volatile oxidation products of the precursors to be vertically transported to regions of very low temperature and to form aerosols there. Sulfate, black carbon, particulate organic matter and mineral dust in HAM2 have longer lifetimes than in HAM1 because of weaker in-cloud scavenging, which is in turn related to lower autoconversion efficiency in the newly introduced two-moment cloud microphysics scheme. Modification in the sea salt emission scheme causes a significant increase in the ratio (from 1.6 to 7.7) between accumulation mode and coarse mode emission fluxes of aerosol number concentration. This leads to a general increase in the number concentration of smaller particles over the oceans in HAM2, as reflected by the higher Ångström parameters. Evaluation against observation reveals that in terms of model performance, main improvements in HAM2 include a marked decrease of the systematic negative bias in the absorption aerosol optical depth, as well as smaller biases over the oceans in Ångström parameter and in the accumulation mode number concentration. The simulated geographical distribution of aerosol optical depth (AOD) is better correlated with the MODIS data, while the surface aerosol mass concentrations are very similar to those in the old version. The total aerosol water content in HAM2 is considerably closer to the multi-model average from Phase I of the AeroCom intercomparison project. Model deficiencies that require further efforts in the future include (i) positive biases in AOD over the ocean, (ii) negative biases in AOD and aerosol mass concentration in high-latitude regions, and (iii) negative biases in particle number concentration, especially that of the Aitken mode, in the lower troposphere in heavily polluted regions.

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The global aerosol-climate model ECHAM-HAM, version 2: sensitivity to improvements in process representations

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-12-7545-2012 ◽

2012 ◽

Vol 12 (3) ◽

pp. 7545-7615 ◽

Cited By ~ 12

Author(s):

K. Zhang ◽

D. O'Donnell ◽

J. Kazil ◽

P. Stier ◽

S. Kinne ◽

...

Keyword(s):

Aerosol Optical Depth ◽

Optical Depth ◽

Water Uptake ◽

Climate Model ◽

Lower Troposphere ◽

Cloud Microphysics ◽

Aerosol Size Distribution ◽

Microphysics Scheme ◽

Temporal Variance ◽

General Improvement

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An advanced scheme for wet scavenging and liquid-phase chemistry in a regional online-coupled chemistry transport model

Atmospheric Chemistry and Physics ◽

10.5194/acp-13-1177-2013 ◽

2013 ◽

Vol 13 (3) ◽

pp. 1177-1192 ◽

Cited By ~ 19

Author(s):

C. Knote ◽

D. Brunner

Keyword(s):

Aqueous Phase ◽

Climate Model ◽

Transport Model ◽

Measurement Data ◽

Coupled System ◽

Cloud Microphysics ◽

Microphysics Scheme ◽

Meteorological Model ◽

Wet Scavenging ◽

Phase Chemistry

Abstract. Clouds are reaction chambers for atmospheric trace gases and aerosols, and the associated precipitation is a major sink for atmospheric constituents. The regional chemistry-climate model COSMO-ART has been lacking a description of wet scavenging of gases and aqueous-phase chemistry. In this work we present a coupling of COSMO-ART with a wet scavenging and aqueous-phase chemistry scheme. The coupling is made consistent with the cloud microphysics scheme of the underlying meteorological model COSMO. While the choice of the aqueous-chemistry mechanism is flexible, the effects of a simple sulfur oxidation scheme are shown in the application of the coupled system in this work. We give details explaining the coupling and extensions made, then present results from idealized flow-over-hill experiments in a 2-D model setup and finally results from a full 3-D simulation. Comparison against measurement data shows that the scheme efficiently reduces SO2 trace gas concentrations by 0.3 ppbv (−30%) on average, while leaving O3 and NOx unchanged. PM10 aerosol mass was increased by 10% on average. While total PM2.5 changes only little, chemical composition is improved notably. Overestimations of nitrate aerosols are reduced by typically 0.5–1 μg m−3 (up to −2 μg m−3 in the Po Valley) while sulfate mass is increased by 1–1.5 μg m−3 on average (up to 2.5 μg m−3 in Eastern Europe). The effect of cloud processing of aerosols on its size distribution, i.e. a shift towards larger diameters, is observed. Compared against wet deposition measurements the system tends to underestimate the total wet deposited mass for the simulated case study.

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Numerical framework and performance of the new multiple-phase cloud microphysics scheme in RegCM4.5: precipitation, cloud microphysics, and cloud radiative effects

Geoscientific Model Development ◽

10.5194/gmd-9-2533-2016 ◽

2016 ◽

Vol 9 (7) ◽

pp. 2533-2547 ◽

Cited By ~ 15

Author(s):

Rita Nogherotto ◽

Adrian Mark Tompkins ◽

Graziano Giuliani ◽

Erika Coppola ◽

Filippo Giorgi

Keyword(s):

Radiative Forcing ◽

Climate Model ◽

Regional Climate ◽

Cloud Microphysics ◽

Microphysics Scheme ◽

Additional Information ◽

Mixing Ratios ◽

Multiple Phase ◽

Realistic Representation ◽

And Performance

Abstract. We implement and evaluate a new parameterization scheme for stratiform cloud microphysics and precipitation within regional climate model RegCM4. This new parameterization is based on a multiple-phase one-moment cloud microphysics scheme built upon the implicit numerical framework recently developed and implemented in the ECMWF operational forecasting model. The parameterization solves five prognostic equations for water vapour, cloud liquid water, rain, cloud ice, and snow mixing ratios. Compared to the pre-existing scheme, it allows a proper treatment of mixed-phase clouds and a more physically realistic representation of cloud microphysics and precipitation. Various fields from a 10-year long integration of RegCM4 run in tropical band mode with the new scheme are compared with their counterparts using the previous cloud scheme and are evaluated against satellite observations. In addition, an assessment using the Cloud Feedback Model Intercomparison Project (CFMIP) Observational Simulator Package (COSP) for a 1-year sub-period provides additional information for evaluating the cloud optical properties against satellite data. The new microphysics parameterization yields an improved simulation of cloud fields, and in particular it removes the overestimation of upper level cloud characteristics of the previous scheme, increasing the agreement with observations and leading to an amelioration of a long-standing problem in the RegCM system. The vertical cloud profile produced by the new scheme leads to a considerably improvement of the representation of the longwave and shortwave components of the cloud radiative forcing.

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Reduced efficacy of marine cloud brightening geoengineering due to in-plume aerosol coagulation: parameterization and global implications

Atmospheric Chemistry and Physics ◽

10.5194/acp-13-10385-2013 ◽

2013 ◽

Vol 13 (20) ◽

pp. 10385-10396 ◽

Cited By ~ 13

Author(s):

G. S. Stuart ◽

R. G. Stevens ◽

A.-I. Partanen ◽

A. K. L. Jenkins ◽

H. Korhonen ◽

...

Keyword(s):

Climate Model ◽

Climate Modeling ◽

Cloud Droplet ◽

Global Scale ◽

Cloud Microphysics ◽

Point Sources ◽

Sea Salt ◽

Sea Spray ◽

Subgrid Scale ◽

Computationally Efficient

Abstract. The intentional enhancement of cloud albedo via controlled sea-spray injection from ships (marine cloud brightening) has been proposed as a possible method to control anthropogenic global warming; however, there remains significant uncertainty in the efficacy of this method due to, amongst other factors, uncertainties in aerosol and cloud microphysics. A major assumption used in recent cloud- and climate-modeling studies is that all sea spray was emitted uniformly into some oceanic grid boxes, and thus these studies did not account for subgrid aerosol coagulation within the sea-spray plumes. We explore the evolution of these sea-salt plumes using a multi-shelled Gaussian plume model with size-resolved aerosol coagulation. We determine how the final number of particles depends on meteorological conditions, including wind speed and boundary-layer stability, as well as the emission rate and size distribution of aerosol emitted. Under previously proposed injection rates and typical marine conditions, we find that the number of aerosol particles is reduced by over 50%, but this reduction varies from under 10% to over 90% depending on the conditions. We provide a computationally efficient parameterization for cloud-resolving and global-scale models to account for subgrid-scale coagulation, and we implement this parameterization in a global-scale aerosol-climate model. While designed to address subgrid-scale coagulation of sea-salt particles, the parameterization is generally applicable for coagulation of subgrid-scale aerosol from point sources. We find that accounting for this subgrid-scale coagulation reduces cloud droplet number concentrations by 46% over emission regions, and reduces the global mean radiative flux perturbation from −1.5 W m−2 to −0.8 W m−2.

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The multi-scale aerosol-climate model PNNL-MMF: model description and evaluation

Geoscientific Model Development Discussions ◽

10.5194/gmdd-3-1625-2010 ◽

2010 ◽

Vol 3 (4) ◽

pp. 1625-1695 ◽

Cited By ~ 2

Author(s):

M. Wang ◽

S. Ghan ◽

R. Easter ◽

M. Ovchinnikov ◽

X. Liu ◽

...

Keyword(s):

Reasonable Agreement ◽

Large Scale ◽

Climate Model ◽

Cloud Microphysics ◽

Chemical Processes ◽

Future Climate Change ◽

Free Troposphere ◽

Microphysics Scheme ◽

New Model ◽

Multi Scale

Abstract. Anthropogenic aerosol effects on climate produce one of the largest uncertainties in estimates of radiative forcing of past and future climate change. Much of this uncertainty arises from the multi-scale nature of the interactions between aerosols, clouds and large-scale dynamics, which are difficult to represent in conventional global climate models (GCMs). In this study, we develop a multi-scale aerosol climate model that treats aerosols and clouds across different scales, and evaluate the model performance, with a focus on aerosol treatment. This new model is an extension of a multi-scale modeling framework (MMF) model that embeds a cloud-resolving model (CRM) within each grid column of a GCM. In this extension, the effects of clouds on aerosols are treated by using an explicit-cloud parameterized-pollutant (ECPP) approach that links aerosol and chemical processes on the large-scale grid with statistics of cloud properties and processes resolved by the CRM. A two-moment cloud microphysics scheme replaces the simple bulk microphysics scheme in the CRM, and a modal aerosol treatment is included in the GCM. With these extensions, this multi-scale aerosol-climate model allows the explicit simulation of aerosol and chemical processes in both stratiform and convective clouds on a global scale. Simulated aerosol budgets in this new model are in the ranges of other model studies. Simulated gas and aerosol concentrations are in reasonable agreement with observations, although the model underestimates black carbon concentrations at the surface. Simulated aerosol size distributions are in reasonable agreement with observations in the marine boundary layer and in the free troposphere, while the model underestimates the accumulation mode number concentrations near the surface, and overestimates the accumulation number concentrations in the free troposphere. Simulated cloud condensation nuclei (CCN) concentrations are within the observational variations. Simulated aerosol optical depth (AOD) and single scattering albedo (SSA) are in reasonable agreement with observations, and the spatial distribution of AOD is consistent with observations, while the model underestimates AOD over regions with strong fossil fuel and biomass burning emissions, and overestimates AOD over regions with strong dust emissions. Overall, this multi-scale aerosol climate model simulates aerosol fields as well as conventional aerosol models.

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SALSA2.0: The sectional aerosol module of the aerosol-chemistry-climate model ECHAM6.3.0-HAM2.3-MOZ1.0

10.5194/gmd-2018-47 ◽

2018 ◽

Cited By ~ 3

Author(s):

Harri Kokkola ◽

Thomas Kühn ◽

Anton Laakso ◽

Tommi Bergman ◽

Kari E. J. Lehtinen ◽

...

Keyword(s):

Climate Model ◽

Stratospheric Aerosol ◽

Aerosol Size Distribution ◽

Global Burden ◽

Size Distributions ◽

Aerosol Chemistry ◽

Microphysics Scheme ◽

Size Dependent ◽

Aerosol Mass ◽

Aerosol Module

Abstract. In this paper, we present the implementation and evaluation of the aerosol microphysics module SALSA2.0 in the framework of the aerosol-chemistry-climate model ECHAM-HAMMOZ. It is an alternative microphysics module to the default modal microphysics scheme M7 in ECHAM-HAMMOZ. The SALSA2.0 implementation is evaluated against the observations of aerosol optical properties, aerosol mass, and size distributions. We also compare the skill of SALSA2.0 in reproducing the observed quantities to the skill of the M7 implementation. The largest differences between SALSA2.0 and M7 are evident over regions where the aerosol size distribution is heavily modified by the microphysical processing of aerosol particles. Such regions are, for example, highly polluted regions and regions strongly affected by biomass burning. In addition, in a simulation of the 1991 Mt Pinatubo eruption in which a stratospheric sulfate plume was formed, the global burden and the effective radii of the stratospheric aerosol are very different in SALSA2.0 and M7. While SALSA2.0 was able to reproduce the observed time evolution of the global burden of sulfate and the effective radii of stratospheric aerosol, M7 strongly overestimates the removal of coarse stratospheric particles and thus underestimates the effective radius of stratospheric aerosol. As the mode widths of M7 have been optimized for the troposphere and were not designed to represent stratospheric aerosol the ability of M7 to simulate the volcano plume was improved by modifying the mode widths decreasing the standard deviations of the accumulation and coarse modes from 1.59 and 2.0, respectively, to 1.2. Overall, SALSA2.0 shows promise in improving the aerosol description of ECHAM-HAMMOZ and can be further improved by implementing methods for aerosol processes that are more suitable for the sectional method, e.g size dependent emissions for aerosol species and size resolved wet deposition.

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Potential for a biogenic influence on cloud microphysics over the ocean: a correlation study with satellite-derived data

Atmospheric Chemistry and Physics ◽

10.5194/acp-12-7977-2012 ◽

2012 ◽

Vol 12 (17) ◽

pp. 7977-7993 ◽

Cited By ~ 34

Author(s):

A. Lana ◽

R. Simó ◽

S. M. Vallina ◽

J. Dachs

Keyword(s):

Cloud Condensation Nuclei ◽

Organic Aerosols ◽

Cloud Droplet ◽

Correlation Study ◽

Cloud Microphysics ◽

Sea Salt ◽

Sea Surface ◽

Radiation Budget ◽

Emission Fluxes ◽

Organic Volatiles

Abstract. Aerosols have a large potential to influence climate through their effects on the microphysics and optical properties of clouds and, hence, on the Earth's radiation budget. Aerosol–cloud interactions have been intensively studied in polluted air, but the possibility that the marine biosphere plays an important role in regulating cloud brightness in the pristine oceanic atmosphere remains largely unexplored. We used 9 yr of global satellite data and ocean climatologies to derive parameterizations of the temporal variability of (a) production fluxes of sulfur aerosols formed by the oxidation of the biogenic gas dimethylsulfide emitted from the sea surface; (b) production fluxes of secondary organic aerosols from biogenic organic volatiles; (c) emission fluxes of biogenic primary organic aerosols ejected by wind action on sea surface; and (d) emission fluxes of sea salt also lifted by the wind upon bubble bursting. Series of global monthly estimates of these fluxes were correlated to series of potential cloud condensation nuclei (CCN) numbers derived from satellite (MODIS). More detailed comparisons among weekly series of estimated fluxes and satellite-derived cloud droplet effective radius (re) data were conducted at locations spread among polluted and clean regions of the oceanic atmosphere. The outcome of the statistical analysis was that positive correlation to CCN numbers and negative correlation to re were common at mid and high latitude for sulfur and organic secondary aerosols, indicating both might be important in seeding cloud droplet activation. Conversely, primary aerosols (organic and sea salt) showed widespread positive correlations to CCN only at low latitudes. Correlations to re were more variable, non-significant or positive, suggesting that, despite contributing to large shares of the marine aerosol mass, primary aerosols are not widespread major drivers of the variability of cloud microphysics. Validation against ground measurements pointed out that the parameterizations used captured fairly well the variability of aerosol production fluxes in most cases, yet some caution is warranted because there is room for further improvement, particularly for primary organic aerosol. Uncertainties and synergies are discussed, and recommendations of research needs are given.

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Global distribution and climate forcing of marine organic aerosol – Part 1: Model improvements and evaluation

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-11-18853-2011 ◽

2011 ◽

Vol 11 (7) ◽

pp. 18853-18899 ◽

Cited By ~ 1

Author(s):

N. Meskhidze ◽

J. Xu ◽

B. Gantt ◽

Y. Zhang ◽

A. Nenes ◽

...

Keyword(s):

Climate Models ◽

Global Climate ◽

Cloud Condensation Nuclei ◽

Organic Aerosols ◽

Organic Aerosol ◽

Number Concentration ◽

Global Climate Models ◽

Sea Salt ◽

Biologically Active ◽

Relative Significance

Abstract. Marine organic aerosol emissions have been implemented and evaluated within the National Center of Atmospheric Research (NCAR)'s Community Atmosphere Model (CAM5) with the Pacific Northwest National Laboratory's 7-mode Modal Aerosol Module (MAM-7). Emissions of marine primary organic aerosols (POA), phytoplankton-produced isoprene- and monoterpenes-derived secondary organic aerosols (SOA) and methane sulfonate (MS−) are shown to affect surface concentrations of organic aerosols in remote marine regions. Global emissions of submicron marine POA is estimated to be 7.9 and 9.4 Tg yr−1, for the Gantt et al. (2011) and Vignati et al. (2010) emission parameterizations, respectively. Marine sources of SOA and particulate MS− (containing both sulfur and carbon atoms) contribute an additional 0.2 and 5.1 Tg yr−1, respectively. Widespread areas over productive waters of the Northern Atlantic, Northern Pacific, and the Southern Ocean show marine-source submicron organic aerosol surface concentrations of 100 ng m−3, with values up to 400 ng m−3 over biologically productive areas. Comparison of long-term surface observations of water insoluble organic matter (WIOM) with POA concentrations from the two emission parameterizations shows that both Gantt et al. (2011) and Vignati et al. (2010) formulations are able to capture the magnitude of marine organic aerosol concentrations, with the Gantt et al. (2011) parameterization attaining better seasonality. Model simulations show that the mixing state of the marine POA can impact the surface number concentration of cloud condensation nuclei (CCN). The largest increases (up to 20 %) in CCN (at a supersaturation (S) of 0.2 %) number concentration are obtained over biologically productive ocean waters when marine organic aerosol is assumed to be externally mixed with sea-salt. Assuming marine organics are internally-mixed with sea-salt provides diverse results with increase and decrease in the concentration of CCN over different parts of the ocean. The sign of the CCN change due to the addition of marine organics to sea-salt aerosol is determined by the relative significance of the increase in mean modal diameter due to addition of mass, and the decrease in particle hygroscopicity due to compositional changes in marine aerosol. Based on emerging evidence for increased CCN concentration over biologically active surface ocean areas/periods, our study suggests that treatment of sea spray in global climate models (GCMs) as an internal mixture of marine organic aerosols and sea-salt will likely lead to an underestimation in CCN number concentration.

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A GCM study of organic matter in marine aerosol and its potential contribution to cloud drop activation

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-7-5675-2007 ◽

2007 ◽

Vol 7 (2) ◽

pp. 5675-5700

Author(s):

G. J. Roelofs

Keyword(s):

Organic Matter ◽

Chemical Composition ◽

Dimethyl Sulfide ◽

Climate Model ◽

Organic Aerosol ◽

Potential Contribution ◽

Marine Aerosol ◽

Mixing State ◽

Cloud Drop ◽

Aerosol Mass

Abstract. With the global aerosol-climate model ECHAM5-HAM we investigate the potential influence of organic aerosol originating from the ocean on aerosol mass and chemical composition and the droplet concentration and size of marine clouds. We present sensitivity simulations in which the uptake of organic matter in the marine aerosol is prescribed for each aerosol mode with varying organic mass and mixing state, and with a geographical distribution and seasonality similar to the oceanic emission of dimethyl sulfide. Measurements of aerosol mass and chemical composition serve to evaluate the representativity of the model initializations. Good agreement with the measurements is obtained when organic matter is added to the Aitken, accumulation and coarse modes simultaneously. Representing marine organics in the model leads to higher cloud drop number concentrations, smaller cloud drop effective radii, and a better agreement with remote sensing measurements. The mixing state of the organics and the other aerosol matter, i.e., internal or external depending on the formation process of aerosol organics, is an important factor for this. We estimate that globally about 75 Tg C yr−1 of organic matter from marine origin enters the aerosol phase. An approximate 35% of this occurs through formation of secondary organic aerosol and 65% through emission of primary particles.

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An advanced scheme for wet scavenging and liquid-phase chemistry in a regional online-coupled chemistry transport model

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-12-26099-2012 ◽

2012 ◽

Vol 12 (10) ◽

pp. 26099-26142

Author(s):

C. Knote ◽

D. Brunner

Keyword(s):

Aqueous Phase ◽

Climate Model ◽

Transport Model ◽

Measurement Data ◽

Coupled System ◽

Cloud Microphysics ◽

Microphysics Scheme ◽

Meteorological Model ◽

Wet Scavenging ◽

Phase Chemistry

Abstract. Clouds are reaction chambers for atmospheric trace gases and aerosols, and the associated precipitation is a major sink for atmospheric constituents. The regional chemistry-climate model COSMO-ART has been lacking a description of wet scavenging of gases and aqueous-phase chemistry. In this work we present a coupling of COSMO-ART with a wet scavenging and aqueous-phase chemistry scheme. The coupling is made consistent with the cloud microphysics scheme of the underlying meteorological model COSMO. While the choice of the aqueous-chemistry mechanism is flexible, the effects of a simple sulfur oxidation scheme are shown in the application of the coupled system in this work. We give details explaining the coupling and extensions made, then present results from idealized flow-over-hill experiments in a 2-D model setup and finally results from a full 3-D simulation. Comparison against measurement data shows that the scheme efficiently reduces SO2 trace gas concentrations by 0.3 ppbv (−30%) on average, while leaving O3 and NOx unchanged. PM10 aerosol mass, which has been overestimated previously, is now in much better agreement with measured values due to a stronger scavenging of coarse particles. While total PM2.5 changes only little, chemical composition is improved notably. Overestimations of nitrate aerosols are reduced by typically 0.5–1 μg m−3 (up to −2 μg m−3 in the Po Valley) while sulfate mass is increased by 1–1.5 μg m−3 on average (up to 2.5 μg m−3 in Eastern Europe). The effect of cloud processing of aerosols on its size distribution, i. e. a shift towards larger diameters, is observed. Compared against wet deposition measurements the system underestimates the total wet deposited mass for the simulated case study. We find that while evaporation of cloud droplets dominates in higher altitudes, evaporation of precipitation can contribute up to 50% of total evaporated mass near the surface.

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