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A mineralogical database is included in the simulation of mineral dust atmospheric life cycle for the chemistry and transport model COSMO5.05-MUSCAT. Evaluation of the ability of the model to reproduce the atmospheric drivers and the spatial-temporal resolution of mineral dust in the atmosphere is done through comparisons with remote sensing measurements in the Sahara Desert region for January-February 2022. Results show simultaneously good agreements and suggest that discrepancies could be explained due to the methods used for calculating mineral dust in the atmosphere not considering compositional differences.

Mineral dust aerosols are composed from a complex assemblage of various minerals depending on the region they originated. Giving the different mineral composition of desert dust aerosols, different physico-chemical properties and therefore varying climate effects are expected. Despite the known regional variations in mineral composition, chemical transport models typically assume that mineral dust 5 aerosols have uniform composition. This study adds, for the first time, mineralogical information to the mineral dust emission scheme used in the chemical transport model COSMO-MUSCAT. We provide a detailed description of the implementation of the mineralogical database, GMINER (Nickovic et al., 2012), together with a specific set of physical parametrizations in the model's mineral dust emission module. These changes lead to a general improvement of the model performance when comparing the simulated mineral dust aerosols with measurements over the Sahara Desert region for January - February 2022 . 10 The simulated mineral dust aerosol vertical distribution is tested by a comparison with aerosol lidar measurements from the lidar system PollyXT, located at Cape Verde. For a lofted mineral dust aerosol layer on the 2 February 5:00 UTC the lidar retrievals yield on a dust mass concentration peak of 156 µg/m³ while the model calculates the mineral dust peak at 136 µg/m³. The results highlight the possibility of using the model with resolved mineral dust composition for interpretation of the lidar measurements since higher absorption the UV-VIS wavelength is correlated to particles having higher hematite 15 content. Additionally, the comparison with in-situ mineralogical measurements of dust aerosol particles show how important they are, but also that more of them are needed for model evaluation. [ABSTRACT FROM AUTHOR]

In Central Asia, climate and air quality are largely affected by local and long-travelled mineral dust. For the last century, the area has experienced severe land-use changes and water exploitation producing new dust sources. Today global warming causes rapid shrinking of mountain glaciers with yet unknow consequences for dust and its climate effects. Despite the importance for a growing population, only little is known about sources, transport pathways and properties of Central Asian dust. A transport study with a global aerosol-climate model is undertaken to investigate the life cycle of mineral dust in Central Asia for the period of a remote-sensing campaign in Tajikistan in 2015–2016. An initial evaluation with sun photometer measurements shows reasonable agreement for the average amount of dust, but a significant weakness of the model in reproducing the seasonality of local dust with maximum activity in summer. Source apportionment reveals a major contribution from Arabia throughout the year in accordance with observations. In the model, local sources mainly contribute in spring and autumn while summer-time dust production is underestimated. The results underline the importance of considering long-range transport and, locally, a detailed representation of atmospheric dynamics and surface characteristics for modelling dust in Central Asia.

The radiative effect of mineral dust and black carbon aerosol are investigated with aerosolclimate model simulations with fixed sea surface temperatures as boundary condition. The semi-direct effects of the absorbing aerosol are assessed as the residual between the total direct radiative effect and the instantaneous direct radiative effect of the aerosol species. For Central Asia the presence of mineral dust aerosol below a black carbon aerosol layer enhances the positive radiative effect of the black carbon aerosol.

The determination of an accurate quantitative understanding of the role of tropospheric aerosols in the earth's radiation budget is extremely important because forcing by anthropogenic aerosols presently represents one of the most uncertain aspects of climate models. Here the authors present a systematic comparison of three different analyses of satellite-retrieved aerosol optical depth based on the Advanced Very High Resolution Radiometer (AVHRR)-measured radiances with optical depths derived from six different models. Also compared are the model-derived clear-sky reflected shortwave radiation with satellite-measured reflectivities derived from the Earth Radiation Budget Experiment (ERBE) satellite. The three different satellite-derived optical depths differ by between -0.10 and 0.07 optical depth units in comparison to the average of the three analyses depending on latitude and month, but the general features of the retrievals are similar. The models differ by between -0.09 and +0.16 optical depth units from the average of the models. Differences between the average of the models and the average of the satellite analyses range over -0.11 to +0.05 optical depth units. These differences are significant since the annual average clear-sky radiative forcing associated with the difference between the average of the models and the average of the satellite analyses ranges between -3.9 and 0.7 W [m.sup.-2] depending on latitude and is -1.7 W [m.sup.-2] on a global average annual basis. Variations in the source strengths of dimethylsulfide-derived aerosols and sea salt aerosols can explain differences between the models, and between the models and satellite retrievals of up to 0.2 optical depth units. The comparison of model-generated reflected shortwave radiation and ERBE-measured shortwave radiation is similar in character as a function of latitude to the analysis of modeled and satellite-retrieved optical depths, but the differences between the modeled clear-sky reflected flux and the ERBE clear-sky reflected flux is generally larger than that inferred from the difference between the models and the AVHRR optical depths, especially at high latitudes. The difference between the mean of the models and the ERBE-analyzed clear-sky flux is 1.6 W [m.sup.-2]. The overall comparison indicates that the model-generated aerosol optical depth is systematically lower than that inferred from measurements between the latitudes of 10 [degrees] and 3 [degrees] S. It is not likely that the shortfall is due to small values of the sea salt optical depth because increases in this component would create modeled optical depths that are larger than those from satellites in the region north of 30 [degrees] N and near 50 [degrees] S. Instead, the source strengths for DMS and biomass aerosols in the models may be too low. Firm conclusions, however, will require better retrieval procedures for the satellites, including better cloud screening procedures, further improvement of the model's treatment of aerosol transport and removal, and a better determination of aerosol source strengths.

Dust from disturbed soils contributes to 50% plus or minus 20% of the atmospheric dust which changes the radiative force and influences the climate. A radioactive transfer model embedded in a general circulation model reveals that the dust from disturbed soils reduces the surface radiation and increases atmospheric heating. This produces variations in the hydrological cycle and in regional circulation patterns that result in variations in the dust sources and atmospheric heating.

More than 1 Tg smoke aerosol was emitted into the atmosphere by the exceptional 2019-2020 Southeast Australian wildfires. Triggered by the extreme fire heat, several deep pyroconvective events carried the smoke directly into the stratosphere. Once there, smoke aerosol remained airborne considerably longer than in lower atmospheric layers. The thick plumes traveled eastward thereby being distributed across the high and mid-latitude Southern Hemisphere enhancing the atmospheric opacity. Due to the increased atmospheric lifetime of the smoke plume its radiative effect increased compared to smoke that remains lower altitudes. Global models describing aerosol-climate impacts show significant uncertainties regarding the emission height of aerosols from intense wildfires. Here, we demonstrate by combination of aerosol-climate modeling and lidar observations the importance of the representation of those high-altitude fire smoke layers for estimating the atmospheric energy budget. In this observation-based approach, the Australian wildfire emissions by pyroconvection are explicitly prescribed to the lower stratosphere in different scenarios. The 2019-2020 Australian fires caused a significant top-of-atmosphere hemispheric instantaneous direct radiative forcing signal that reached a magnitude comparable to the radiative forcing induced by anthropogenic absorbing aerosol. Up to +0.50 W m-2 instantaneous direct radiative forcing was modeled at top of the atmosphere, averaged for the Southern Hemisphere for January to March 2020 under all-sky conditions. While at the surface, an instantaneous solar radiative forcing of up to -0.81 W m-2 was found for clear-sky conditions, depending on the model configuration. Since extreme wildfires are expected to occur more frequently in the rapidly changing climate, our findings suggest that deep wildfire plumes must be adequately considered in climate projections in order to obtain reasonable estimates of atmospheric energy budget changes. [ABSTRACT FROM AUTHOR]

Mineral dust particles play an important role in the climate system, by e.g. interacting with solar and terrestrial radiation or facilitating the formation of cloud droplets. Additionally, dust particles can act as very efficient ice nuclei in cirrus clouds. Many Global Chemistry Climate Models (GCCMs) use prescribed monthly mean mineral dust emissions representative of a specific year, based on a climatology. It was hypothesized that using dust emission climatologies may lead to misrepresentations of strong dust burst episodes, resulting in a negative bias of model dust concentrations compared to observations for these episodes. Here, we apply the aerosol microphysics submodel MADE3 (Modal Aerosol Dynamics model for Europe, adapted for global applications, third generation) as part of the ECHAM/MESSy Atmospheric Chemistry (EMAC) general circulation model. We employ two different representations of mineral dust for our model simulations: i) a prescribed monthly-mean climatology of dust emissions representative of the year 2000; ii) an online dust parametrization which calculates wind-driven mineral dust emissions at every model time-step. We evaluate model results for these two dust representations by comparison with observations of aerosol optical depth from ground-based station data. The model results show a better agreement with the observations for strong dust burst events when using the online dust representation compared to the prescribed dust emissions setup. Furthermore, we analyse the effect of increasing the vertical and horizontal model resolution on mineral dust properties in our model. The model is evaluated against airborne in situ measurements performed during the SALTRACE mineral dust campaign (Saharan Aerosol Long-range Transport and Aerosol-Cloud Interaction Experiment, June/July 2013), i.e. observations of dust transported from the Sahara to the Caribbean. Results show that an increased horizontal and vertical model resolution is able to better represent the spatial distribution of airborne mineral dust, especially in the upper troposphere (above 400 hPa). Additionally, we analyse the effect of varying assumptions for the size distribution of emitted dust. The results of this study will help to identify the model setup best suited for future studies and to further improve the representation of mineral dust particles in EMAC-MADE3. [ABSTRACT FROM AUTHOR]

A new cloud microphysical scheme including a detailed parameterization for aerosol-driven ice formation in cirrus clouds is implemented in the global chemistry climate model EMAC and coupled to the aerosol submodel MADE3. The new scheme is able to consistently simulate three regimes of stratiform clouds (liquid, mixed- and ice-phase (cirrus) clouds), considering the impact of aerosol on the activation of cloud droplets and the nucleation of ice crystals. In the cirrus regime, it accounts for the competition between homogeneous and heterogeneous freezing for the available supersaturated water vapor, taking into account different types of ice-nucleating particles, whose specific ice-nucleating properties can be flexibly varied in the model setup. The new model configuration was tuned using satellite data to find the optimal set of parameters that reproduces the observations. A detailed evaluation is also performed comparing the model results for standard cloud and radiation variables with a comprehensive set of observations from satellite retrievals and in situ measurements. The performance of EMAC-MADE3 in this new coupled configuration is in line with similar global coupled models and with other global aerosol models featuring ice cloud parameterizations. Some remaining discrepancies, especially with regard to ice crystal number concentrations in cirrus, which are a common problem of this kind of models, need to be the subject of future investigations. To further demonstrate the readiness of the new model system for application studies, an estimate of the global anthropogenic aerosol radiative forcing is provided and discussed in the context of the CMIP5 results for the IPCC. [ABSTRACT FROM AUTHOR]

The spatial distribution and properties of submicron organic aerosols (OA) are among the key sources of uncertainty in our understanding of aerosol effects on climate. Uncertainties are particularly large over remote regions of the free troposphere and Southern Ocean, where very little data has been available, and where OA predictions from AeroCom Phase II global models span a factor of 400–1000, greatly exceeding the model spread over source regions. The (nearly) pole-to-pole vertical distribution of non-refractory aerosols was measured with an aerosol mass spectrometer onboard the NASA DC8 aircraft as part of the Atmospheric Tomography (ATom) mission during the northern hemisphere summer (August 2016) and winter (February 2017). This study presents the first extensive characterization of OA mass concentrations and their level of oxidation in the remote atmosphere. OA and sulfate are the major contributors by mass to submicron aerosols in the remote troposphere, together with sea salt in the marine boundary layer. Sulfate was dominant in the lower stratosphere. OA concentrations have a strong seasonal and zonal variability, with the highest levels measured in the summer and over the regions influenced by the biomass burning from Africa (up to 10 μg sm−3). Lower concentrations (~ 0.1–0.3 μg sm−3) are observed in the northern mid- and high-latitudes and very low concentrations (< 0.1 μg sm−3) in the southern mid- and high-latitudes. The ATom dataset is used to evaluate predictions of eight current global chemistry models that implement a variety of commonly used representations of OA sources and chemistry, as well as of the AeroCom-II ensemble. The current model ensemble captures the average vertical and spatial distribution of measured OA concentrations, and the spread of the individual models remains within a factor of 5. These results are significantly improved over the AeroCom-II model ensemble, which shows large overestimations over these regions. However, some of the improved agreement with observations occurs for the wrong reasons, as models have the tendency to greatly overestimate the primary OA fraction, and underestimate the secondary fraction. Measured OA in the remote free troposphere are highly oxygenated with organic aerosol to organic carbon (OA / OC) ratios of ~ 2.2–2.8 and are 30–60 % more oxygenated than in current models, which can lead to significant errors in OA concentrations. The model/measurement comparisons presented here support the concept of a more dynamic OA system as proposed by Hodzic et al. (2016), with enhanced removal of primary OA, and a stronger production of secondary OA in global models needed to provide a better agreement with observations. [ABSTRACT FROM AUTHOR]