In this study, a global variable-resolution modeling framework of atmospheric dust and its radiative feedback is established and evaluated. In this model, atmospheric dust is simulated simultaneously with meteorological fields, and dust-radiation interactions are included. Five configurations of global mesh with refinement at different resolutions and over different regions are used to explore the impacts of regional refinement on modeling dust lifecycle at regional and global scales. The model reasonably produces the overall magnitudes and spatial variabilities of global dust metrics such as surface mass concentration, deposition, aerosol optical depth, and radiative forcing compared to observations and previous modeling results. Two global variable-resolution simulations with mesh refinement over major deserts of North Africa (V16 km-NA) and East Asia (V16 km-EA) simulate less dust emissions and smaller dry deposition rates inside the refined regions due to the weakened near-surface wind speed caused by better resolved topographic complexity at higher resolution. The dust mass loadings over North Africa are close to each other between V16 km-NA and the quasi-uniform resolution (similar to 120 km) (U120 km), while over East Asia, V16 km-EA simulates higher dust mass loading. Over the non-refined areas with the same resolution, the difference between global variable-resolution and uniform-resolution experiments also exists, which is partly related to their difference in dynamic time-step and the coefficient for horizontal diffusion. Refinement at convection-permitting resolution around the Tibetan Plateau (TP) simulates less dust due to its more efficient wet scavenging from resolved convective precipitation around the TP against coarse resolution. Mineral dust plays an important role in Earth's climate system. Numerical simulation of dust and its impacts on a regional scale still has large uncertainties, partly due to the relatively coarse horizontal resolution. Limited-area simulation at relatively high resolution can generally better characterize dust and its impacts on a regional scale; however, lateral boundary conditions may introduce some numerical issues and constrain regional feedback, such as dust-cloud and dust-radiation interactions, to large-scale circulation. In this study, a novel modeling framework of atmospheric dust and its climatic feedbacks with the capability of global variable-resolution simulation is established and evaluated. The model produces reasonable global spatial distributions of dust compared to observations and previous studies. The difference between the simulations at global quasi-uniform resolution and global variable resolution with regional refinement over East Asia and North Africa is significant, particularly with refinement at convection-permitting resolution. This model may be used in the future to provide new insights into the impacts of dust on regional and global climate systems. A modeling framework of atmospheric dust with the capability of global variable-resolution simulation is introduced and evaluatedExperiments with regional refinement produce less dust emissions and mass loading and smaller dry deposition due to weaker surface windRefinement at convection-permitting resolution simulates stronger wet scavenging and less dust mass compared to coarse resolution

In this work, we report the ongoing implementation of online-coupled aerosol-cloud microphysical-radiation interactions in the Brazilian global atmospheric model (BAM) and evaluate the initial results, using remote-sensing data for JFM 2014 and JAS 2019. Rather than developing a new aerosol model, which incurs significant overheads in terms of fundamental research and workforce, a simplified aerosol module from a preexisting global aerosol-chemistry-climate model is adopted. The aerosol module is based on a modal representation and comprises a suite of aerosol microphysical processes. Mass and number mixing ratios, along with dry and wet radii, are predicted for black carbon, particulate organic matter, secondary organic aerosols, sulfate, dust, and sea salt aerosols. The module is extended further to include physically based parameterization for aerosol activation, vertical mixing, ice nucleation, and radiative optical properties computations. The simulated spatial patterns of surface mass and number concentrations are similar to those of other studies. The global means of simulated shortwave and longwave cloud radiative forcing are comparable with observations with normalized mean biases <= 11% and <= 30%, respectively. Large positive bias in BAM control simulation is enhanced with the inclusion of aerosols, resulting in strong overprediction of cloud optical properties. Simulated aerosol optical depths over biomass burning regions are moderately comparable. A case study simulating an intense biomass burning episode in the Amazon is able to reproduce the transport of smoke plumes towards the southeast, thus showing a potential for improved forecasts subject to using near-real-time remote-sensing fire products and a fire emission model. Here, we rely completely on remote-sensing data for the present evaluation and restrain from comparing our results with previous results until a complete representation of the aerosol lifecycle is implemented. A further step is to incorporate dry deposition, in-cloud and below-cloud scavenging, sedimentation, the sulfur cycle, and the treatment of fires.

Aerosol absorption constitutes a significant component of the total radiative effect of aerosols, and hence its representation in general circulation models is crucial to radiative forcing estimates. We use here multiple observations to evaluate the performance of CAM5.3-Oslo with respect to its aerosol representation. CAM5.3-Oslo is the atmospheric component of the earth system model NorESM1.2 and shows on average an underestimation of aerosol absorption in the focus region over East and South Asia and a strong aerosol absorption overestimation in desert and arid regions compared to observations and other AeroCom phase III models. We explore the reasons of the model spread and find that it is related to the column burden and residence time of absorbing aerosols, in particular black carbon and dust. We conduct further sensitivity simulations with CAM5.3-Oslo to identify processes which are most important for modelled aerosol absorption. The sensitivity experiments target aerosol optical properties, and contrast their impact with effects from changes in emissions and deposition processes, and the driving meteorology. An improved agreement with observations was found with the use of a refined emission data set, transient emissions and assimilation of meteorological observations. Changes in optical properties of absorbing aerosols can also reduce the under- and overestimation of aerosol absorption in the model. However, changes in aerosol absorption strength between the sensitivity experiments are small compared to the inter-model spread among the AeroCom phase III models.

This study presents an assessment of the impact of black carbon (BC) regional emissions of four Nordic countries (Denmark, Finland, Norway and Sweden - denoted henceforth as DFNS). The surface concentrations, radiative forcing and BC-in-snow forcing were calculated using ECHAM-HAMMOZ global aerosol-climate model and, where possible, evaluated with field observations. We found that the model is reproducing the BC surface concentrations for most of the measurement sites considered within 1-2 standard deviations, with only few exceptions. The radiative forcing (top of the atmosphere, short-wave, clear and total sky) of BC emitted in DFNS on regional (Nordic and Arctic area separately) and global levels was calculated by removing the anthropogenic emissions from DFNS. The total values for clear sky for the three regions are 16.2 +/- 1.4, 2.9 +/- 0.28 and 0.04 +/- 0.022mW/m(2), respectively. The presence of clouds enhanced the BC radiative forcing. The forcing caused by BC deposited on snow is roughly equal to the direct radiative forcing of airborne BC (17.3 +/- 3.34mW/m(2) over DFNS, 4.2 +/- 0.77mW/m(2) over the Arctic and 0.042 +/- 0.012mW/m(2) globally).

Observational evidence demonstrates that marine organic aerosols (MOA) are able to act as ice nuclei. MOA explains a substantial portion of the submicron marine aerosol, so that they have the potential to effectively influence marine cloud microphysics and cloud radiative forcing. This study provides the first evaluation of the radiative forcing and climatic impact of marine organic aerosols as ice nuclei on a global scale. MOA is implemented into a coupled aerosol and general circulation model. It is found that MOA contributes to more ice formation than dust or black carbon/organic matter in mixed-phase clouds. They also have a significant impact on the ice water path in the Southern Hemisphere and therefore could be an important missing source of ice nuclei in current models. The addition of MOA as natural heterogeneous ice nuclei reduces the magnitude of the total top-of-atmosphere anthropogenic aerosol forcing by as much as 0.3 W/m(2).

[1] The Model for Integrated Research on Atmospheric Global Exchanges ( MIRAGE) modeling system, designed to study the impacts of anthropogenic aerosols on the global environment, is described. MIRAGE consists of a chemical transport model coupled online with a global climate model. The chemical transport model simulates trace gases, aerosol number, and aerosol chemical component mass ( sulfate, methane sulfonic acid (MSA), organic matter, black carbon ( BC), sea salt, and mineral dust) for four aerosol modes (Aitken, accumulation, coarse sea salt, and coarse mineral dust) using the modal aerosol dynamics approach. Cloud-phase and interstitial aerosol are predicted separately. The climate model, based on Community Climate Model, Version 2 (CCM2), has physically based treatments of aerosol direct and indirect forcing. Stratiform cloud water and droplet number are simulated using a bulk microphysics parameterization that includes aerosol activation. Aerosol and trace gas species simulated by MIRAGE are presented and evaluated using surface and aircraft measurements. Surface-level SO2 in North American and European source regions is higher than observed. SO2 above the boundary layer is in better agreement with observations, and surface-level SO2 at marine locations is somewhat lower than observed. Comparison with other models suggests insufficient SO2 dry deposition; increasing the deposition velocity improves simulated SO2. Surface-level sulfate in North American and European source regions is in good agreement with observations, although the seasonal cycle in Europe is stronger than observed. Surface-level sulfate at high-latitude and marine locations, and sulfate above the boundary layer, are higher than observed. This is attributed primarily to insufficient wet removal; increasing the wet removal improves simulated sulfate at remote locations and aloft. Because of the high sulfate bias, radiative forcing estimates for anthropogenic sulfur given in 2001 by S. J. Ghan and colleagues are probably too high. Surface- level dimethyl sulfide (DMS) is similar to 40% higher than observed, and the seasonal cycle shows too much DMS in local winter, partially caused by neglect of oxidation by NO3. Surface-level MSA at marine locations is similar to80% higher than observed, also attributed to insufficient wet removal. Surface- level BC is similar to 50% lower than observed in the United States and similar to 40% lower than observed globally. Treating BC as initially hydrophobic would lessen this bias. Surface- level organic matter is lower than observed in the United States, similar to BC, but shows no bias in the global comparison. Surface- level sea salt concentrations are similar to 30% lower than observed, partly caused by low temporal variance of the model's 10 m wind speeds. Submicrometer sea salt is strongly underestimated by the emissions parameterization. Dust concentrations are within a factor of 3 at most sites but tend to be lower than observed, primarily because of neglect of very large particles and underestimation of emissions and vertical transport under high-wind conditions. Accumulation and Aitken mode number concentrations and mean sizes at the surface over ocean, and condensation nuclei concentrations aloft over the Pacific, are in fair agreement with observations. Concentrations over land are generally higher than observations, with mean sizes correspondingly lower than observations, especially at some European locations. Increasing the assumed size of emitted particles produces better agreement at the surface over land, and reduci

A three-dimensional aerosol transport-radiation model coupled with a general circulation model, Spectral Radiation-Transport Model for Aerosol Species (SPRINTARS), simulates atmospheric aerosol distributions and optical properties. The simulated results are compared with aerosol sampling and optical observations from ground, aircraft, and satellite acquired by intensive observation campaigns over east Asia in spring 2001. Temporal variations of the aerosol concentrations, optical thickness, and Angstrom exponent are in good agreement between the simulation and observations. The midrange values of the Angstrom exponent, even at the Asian dust storm events over the outflow regions, suggest that the contribution of the anthropogenic aerosol, such as carbonaceous and sulfate, to the total optical thickness is of an order comparable to that of the Asian dust. The radiative forcing by the aerosol direct and indirect effects is also calculated. The negative direct radiative forcing is simulated to be over -10 W m(-2) at the tropopause in the air mass during the large-scale dust storm, to which both anthropogenic aerosols and Asian dust contribute almost equivalently. The direct radiative forcing, however, largely depends on the cloud water content and the vertical profiles of aerosol and cloud. The simulation shows that not only sulfate and sea salt aerosols but also black carbon and soil dust aerosols, which absorb solar and thermal radiation, make strong negative radiative forcing by the direct effect at the surface, which may exceed the positive forcing by anthropogenic greenhouse gases over the east Asian region.