The spatial distribution of mineral dust and its shortwave radiative forcing over North Africa: modeling sensitivities to dust emissions and aerosol size treatments

Abstract. A fully coupled meteorology-chemistry-aerosol model (WRF-Chem) is applied to simulate mineral dust and its shortwave (SW) radiative forcing over North Africa. Two dust emission schemes (GOCART and DUSTRAN) and two aerosol models (MADE/SORGAM and MOSAIC) are adopted in simulations to investigate the modeling sensitivities to dust emissions and aerosol size treatments. The modeled size distribution and spatial variability of mineral dust and its radiative properties are evaluated using measurements (ground-based, aircraft, and satellites) during the AMMA SOP0 campaign from 6 January to 3 February of 2006 (the SOP0 period) over North Africa. Two dust emission schemes generally simulate similar spatial distributions and temporal evolutions of dust emissions. Simulations using the GOCART scheme with different initial (emitted) dust size distributions show that the difference of initial dust size distributions can result in significant difference (up to ~50%) in simulating SW dust heating and SW dust radiative forcing at the surface over the Sahel region. The modal approach of MADE/SORGAM retains 25% more fine dust particles (radius <1.25 μm) but 8% less coarse dust particles (radius >1.25 μm) than the sectional approach of MOSAIC in simulations using the same size-resolved dust emissions. Consequently, MADE/SORGAM simulates 11% higher AOD, up to 13% lower SW dust heating rate, and 15% larger (more negative) SW dust radiative forcing at the surface than MOSAIC over the Sahel region. In the daytime of the SOP0 period, the model simulations show that mineral dust heats the lower atmosphere (1–3 km) with a maximum rate of 0.8±0.5 K day−1 below 1 km and reduces the downwelling SW radiation at the surface by up to 58 W m−2 over the Sahel region. This highlights the importance of including dust radiative impact in understanding the regional climate of North Africa. When compared to the available measurements, the WRF-Chem simulations can generally capture the measured features of mineral dust and its radiative properties over North Africa, suggesting that the model is suitable for more extensive simulations of dust impact on regional climate over North Africa.

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The spatial distribution of mineral dust and its shortwave radiative forcing over North Africa: modeling sensitivities to dust emissions and aerosol size treatments

Atmospheric Chemistry and Physics ◽

10.5194/acp-10-8821-2010 ◽

2010 ◽

Vol 10 (18) ◽

pp. 8821-8838 ◽

Cited By ~ 174

Author(s):

C. Zhao ◽

X. Liu ◽

L. R. Leung ◽

B. Johnson ◽

S. A. McFarlane ◽

...

Keyword(s):

North Africa ◽

Radiative Forcing ◽

Mineral Dust ◽

Regional Climate ◽

Dust Emission ◽

Radiative Properties ◽

Lower Atmosphere ◽

Dust Particles ◽

Dust Emissions ◽

Sahel Region

Abstract. A fully coupled meteorology-chemistry-aerosol model (WRF-Chem) is applied to simulate mineral dust and its shortwave (SW) radiative forcing over North Africa. Two dust emission schemes (GOCART and DUSTRAN) and two aerosol models (MADE/SORGAM and MOSAIC) are adopted in simulations to investigate the modeling sensitivities to dust emissions and aerosol size treatments. The modeled size distribution and spatial variability of mineral dust and its radiative properties are evaluated using measurements (ground-based, aircraft, and satellites) during the AMMA SOP0 campaign from 6 January to 3 February of 2006 (the SOP0 period) over North Africa. Two dust emission schemes generally simulate similar spatial distributions and temporal evolutions of dust emissions. Simulations using the GOCART scheme with different initial (emitted) dust size distributions require ~40% difference in total emitted dust mass to produce similar SW radiative forcing of dust over the Sahel region. The modal approach of MADE/SORGAM retains 25% more fine dust particles (radius<1.25 μm) but 8% less coarse dust particles (radius>1.25 μm) than the sectional approach of MOSAIC in simulations using the same size-resolved dust emissions. Consequently, MADE/SORGAM simulates 11% higher AOD, up to 13% lower SW dust heating rate, and 15% larger (more negative) SW dust radiative forcing at the surface than MOSAIC over the Sahel region. In the daytime of the SOP0 period, the model simulations show that the mineral dust heats the lower atmosphere with an average rate of 0.8 ± 0.5 K day−1 over the Niamey vicinity and 0.5 ± 0.2 K day−1 over North Africa and reduces the downwelling SW radiation at the surface by up to 58 W m−2 with an average of 22 W m−2 over North Africa. This highlights the importance of including dust radiative impact in understanding the regional climate of North Africa. When compared to the available measurements, the WRF-Chem simulations can generally capture the measured features of mineral dust and its radiative properties over North Africa, suggesting that the model is suitable for more extensive simulations of dust impact on regional climate over North Africa.

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Sensitivity of the WRF-Chem (V3.6.1) model to different dust emission parametrisation: assessment in the broader Mediterranean region

Geoscientific Model Development ◽

10.5194/gmd-10-2925-2017 ◽

2017 ◽

Vol 10 (8) ◽

pp. 2925-2945 ◽

Cited By ~ 17

Author(s):

Emmanouil Flaounas ◽

Vassiliki Kotroni ◽

Konstantinos Lagouvardos ◽

Martina Klose ◽

Cyrille Flamant ◽

...

Keyword(s):

North Africa ◽

Eastern Mediterranean ◽

Dust Emission ◽

Model Performance ◽

Dust Particles ◽

Dust Transport ◽

Dust Emissions ◽

Extinction Coefficients ◽

Airborne Measurements ◽

Model Aerosol

Abstract. In this study we aim to assess the WRF-Chem model capacity to reproduce dust transport over the eastern Mediterranean. For this reason, we compare the model aerosol optical depth (AOD) outputs to observations, focusing on three key regions: North Africa, the Arabian Peninsula and the eastern Mediterranean. Three sets of four simulations have been performed for the 6-month period of spring and summer 2011. Each simulation set uses a different dust emission parametrisation and for each parametrisation, the dust emissions are multiplied with various coefficients in order to tune the model performance. Our assessment approach is performed across different spatial and temporal scales using AOD observations from satellites and ground-based stations, as well as from airborne measurements of aerosol extinction coefficients over the Sahara. Assessment over the entire domain and simulation period shows that the model presents temporal and spatial variability similar to observed AODs, regardless of the applied dust emission parametrisation. On the other hand, when focusing on specific regions, the model skill varies significantly. Tuning the model performance by applying a coefficient to dust emissions may reduce the model AOD bias over a region, but may increase it in other regions. In particular, the model was shown to realistically reproduce the major dust transport events over the eastern Mediterranean, but failed to capture the regional background AOD. Further comparison of the model simulations to airborne measurements of vertical profiles of extinction coefficients over North Africa suggests that the model realistically reproduces the total atmospheric column AOD. Finally, we discuss the model results in two sensitivity tests, where we included finer dust particles (less than 1 µm) and changed accordingly the dust bins' mass fraction.

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Potential Dust Induced Changes on the Seasonal Variability of Temperature Extremes Over the Sahel: A Regional Climate Modeling Study

Frontiers in Earth Science ◽

10.3389/feart.2020.591150 ◽

2021 ◽

Vol 8 ◽

Author(s):

Ibrahima Diba ◽

Jules Basse ◽

Mamadou Ndiaye ◽

Hamady Ngansou Sabaly ◽

Arona Diedhiou ◽

...

Keyword(s):

Energy Demand ◽

Climate Model ◽

Mineral Dust ◽

Climate Modeling ◽

Regional Climate ◽

Heat Index ◽

Dust Particles ◽

Temperature Extremes ◽

Dust Emissions ◽

The Impact

The aim of this study is to simulate the impact of mineral dust emissions from the Sahel–Saharan zone on temperature extremes over the Sahel. To achieve this goal, we performed two numerical simulations: one with the standard version of the regional climate model RegCM4 (no dust run) and another one with the same version of this model incorporating a dust module (dust run). The difference between both versions of the model allowed to isolate the impacts of mineral dust emissions on temperature extremes. The results show that the accumulation of mineral dust into the atmosphere leads to a decrease of the frequency of warm days, very warm days, and warm nights over the Sahel. This decrease is higher during the MAM (March-April-May) and JJA (June-July-August) periods especially in the northern and western parts of the Sahel. The impact of the mineral dust emissions is also manifested by a decrease of the frequency of tropical nights especially during MAM in the northern Sahel. When considering the warm spells, mineral particles tend to weaken them especially in MAM and JJA in the northern Sahel. To estimate the potential impacts of the mineral dust accumulation on heat stress, the heat index and the humidex are used. The analysis of the heat index shows that the dust impact is to reduce the health risks particularly in the northern Sahel during the MAM period, in the western Sahel during JJA, and in the southern and the northeastern parts of the Sahel during the SON (September-October-November) period. As for the humidex, it is characterized by a decrease especially in the northern Sahel for all seasons. This reduction of the occurrence of thermal extremes may have a positive effect on the energy demand for cooling and on global health. However, the accumulation of dust particles in the atmosphere may also increase the meningitis incidence and prevalence.

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Mineral dust modelling with MADE3 in EMAC v2.54

10.5194/gmd-2020-82 ◽

2020 ◽

Author(s):

Christof G. Beer ◽

Johannes Hendricks ◽

Mattia Righi ◽

Bernd Heinold ◽

Ina Tegen ◽

...

Keyword(s):

Atmospheric Chemistry ◽

General Circulation ◽

Climate Models ◽

Mineral Dust ◽

Dust Emission ◽

Circulation Model ◽

Dust Particles ◽

Model Resolution ◽

Time Step ◽

Dust Emissions

Abstract. 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.

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U.K. HiGEM: Impacts of Desert Dust Radiative Forcing in a High-Resolution Atmospheric GCM

Journal of Climate ◽

10.1175/jcli-d-13-00556.1 ◽

2014 ◽

Vol 27 (15) ◽

pp. 5907-5928 ◽

Cited By ~ 9

Author(s):

M. J. Woodage ◽

S. Woodward

Keyword(s):

Particle Size ◽

High Resolution ◽

Particle Size Distribution ◽

Size Distribution ◽

Radiative Forcing ◽

Mineral Dust ◽

West African Monsoon ◽

Radiative Properties ◽

Saharan Dust ◽

Dust Particles

Abstract This work investigates the impacts of mineral dust aerosol on climate using the atmospheric component of the U.K. High-Resolution Global Environmental Model (HiGEM) with an interactive embedded mineral dust scheme. It extends earlier work by Woodage et al. in which direct radiative forcing due to dust was calculated and in which it was reported that the global total dust burden was increased when this was included in the model. Here this result is analyzed further and the regional and global impacts are investigated. It is found that particle size distribution is critically important: In regions where large, more absorbent dust particles are present, burdens are increased because of the enhanced heating aloft, which strengthens convection, whereas, in areas where smaller, more scattering particles dominate, the surface layers are stabilized and dust emissions are decreased. The consequent changes in dust load and particle size distribution when radiative effects are included make the annual mean global forcing more positive at the top of the atmosphere (0.33 versus 0.05 W m−2). Impacts on the West African monsoon are also considered, where Saharan dust brings about a northward shift in the summertime intertropical convergence zone with increased precipitation on its northern side. This contrasts with results from some other studies, but the authors’ findings are supported by recent observational data. They argue that the impacts depend crucially on the size distribution and radiative properties of the dust particles, which are poorly known on a global scale and differ here from those used in other models.

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Modelling mineral dust emissions and atmospheric dispersion with MADE3 in EMAC v2.54

Geoscientific Model Development ◽

10.5194/gmd-13-4287-2020 ◽

2020 ◽

Vol 13 (9) ◽

pp. 4287-4303

Author(s):

Christof G. Beer ◽

Johannes Hendricks ◽

Mattia Righi ◽

Bernd Heinold ◽

Ina Tegen ◽

...

Keyword(s):

Atmospheric Chemistry ◽

General Circulation ◽

Climate Models ◽

Mineral Dust ◽

Dust Emission ◽

Circulation Model ◽

Dust Particles ◽

Model Resolution ◽

Time Step ◽

Dust Emissions

Abstract. It was hypothesized that using mineral dust emission climatologies in global chemistry climate models (GCCMs), i.e. prescribed monthly-mean dust emissions representative of a specific year, may lead to misrepresentations of strong dust burst events. This could result 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 emissions for our model simulations: (i) a prescribed monthly-mean climatology of dust emissions representative of the year 2000 and (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 the mineral dust properties in our model. We compare results from simulations with T42L31 and T63L31 model resolution (2.8∘×2.8∘ and 1.9∘×1.9∘ in latitude and longitude, respectively; 31 vertical levels) with the reference setup (T42L19). The different model versions are 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 but find only a weak sensitivity concerning these changes. 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.

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Impact of Desert Dust Radiative Forcing on Sahel Precipitation: Relative Importance of Dust Compared to Sea Surface Temperature Variations, Vegetation Changes, and Greenhouse Gas Warming

Journal of Climate ◽

10.1175/jcli4056.1 ◽

2007 ◽

Vol 20 (8) ◽

pp. 1445-1467 ◽

Cited By ~ 234

Author(s):

Masaru Yoshioka ◽

Natalie M. Mahowald ◽

Andrew J. Conley ◽

William D. Collins ◽

David W. Fillmore ◽

...

Keyword(s):

Surface Temperature ◽

Sea Surface Temperature ◽

North Africa ◽

Radiative Forcing ◽

Sea Surface ◽

Desert Dust ◽

Direct Radiative Forcing ◽

Sahel Region ◽

Precipitation Reduction ◽

Sahel Precipitation

Abstract The role of direct radiative forcing of desert dust aerosol in the change from wet to dry climate observed in the African Sahel region in the last half of the twentieth century is investigated using simulations with an atmospheric general circulation model. The model simulations are conducted either forced by the observed sea surface temperature (SST) or coupled with the interactive SST using the Slab Ocean Model (SOM). The simulation model uses dust that is less absorbing in the solar wavelengths and has larger particle sizes than other simulation studies. As a result, simulations show less shortwave absorption within the atmosphere and larger longwave radiative forcing by dust. Simulations using SOM show reduced precipitation over the intertropical convergence zone (ITCZ) including the Sahel region and increased precipitation south of the ITCZ when dust radiative forcing is included. In SST-forced simulations, on the other hand, significant precipitation changes are restricted to over North Africa. These changes are considered to be due to the cooling of global tropical oceans as well as the cooling of the troposphere over North Africa in response to dust radiative forcing. The model simulation of dust cannot capture the magnitude of the observed increase of desert dust when allowing dust to respond to changes in simulated climate, even including changes in vegetation, similar to previous studies. If the model is forced to capture observed changes in desert dust, the direct radiative forcing by the increase of North African dust can explain up to 30% of the observed precipitation reduction in the Sahel between wet and dry periods. A large part of this effect comes through atmospheric forcing of dust, and dust forcing on the Atlantic Ocean SST appears to have a smaller impact. The changes in the North and South Atlantic SSTs may account for up to 50% of the Sahel precipitation reduction. Vegetation loss in the Sahel region may explain about 10% of the observed drying, but this effect is statistically insignificant because of the small number of years in the simulation. Greenhouse gas warming seems to have an impact to increase Sahel precipitation that is opposite to the observed change. Although the estimated values of impacts are likely to be model dependent, analyses suggest the importance of direct radiative forcing of dust and feedbacks in modulating Sahel precipitation.

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Dust emission size distribution impact on aerosol budget and radiative forcing over the Mediterranean region: a regional climate model approach

Atmospheric Chemistry and Physics ◽

10.5194/acp-12-10545-2012 ◽

2012 ◽

Vol 12 (21) ◽

pp. 10545-10567 ◽

Cited By ~ 55

Author(s):

P. Nabat ◽

F. Solmon ◽

M. Mallet ◽

J. F. Kok ◽

S. Somot

Keyword(s):

Size Distribution ◽

Radiative Forcing ◽

Mediterranean Basin ◽

Climate Model ◽

Regional Climate ◽

Dust Emission ◽

Dust Deposition ◽

The Mediterranean ◽

Dust Distribution ◽

The Mediterranean Basin

Abstract. The present study investigates the dust emission and load over the Mediterranean basin using the coupled chemistry–aerosol–regional climate model RegCM-4. The first step of this work focuses on dust particle emission size distribution modeling. We compare a parameterization in which the emission is based on the individual kinetic energy of the aggregates striking the surface to a recent parameterization based on an analogy with the fragmentation of brittle materials. The main difference between the two dust schemes concerns the mass proportion of fine aerosol that is reduced in the case of the new dust parameterization, with consequences for optical properties. At the episodic scale, comparisons between RegCM-4 simulations, satellite and ground-based data show a clear improvement using the new dust distribution in terms of aerosol optical depth (AOD) values and geographic gradients. These results are confirmed at the seasonal scale for the investigated year 2008. This change of dust distribution has sensitive impacts on the simulated regional dust budget, notably dry dust deposition and the regional direct aerosol radiative forcing over the Mediterranean basin. In particular, we find that the new size distribution produces a higher dust deposition flux, and smaller top of atmosphere (TOA) dust radiative cooling. A multi-annual simulation is finally carried out using the new dust distribution over the period 2000–2009. The average SW radiative forcing over the Mediterranean Sea reaches −13.6 W m−2 at the surface, and −5.5 W m−2 at TOA. The LW radiative forcing is positive over the basin: 1.7 W m−2 on average over the Mediterranean Sea at the surface, and 0.6 W m−2 at TOA.

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Homogeneized modeling of mineral dust emissions over Europe and Africa using the CHIMERE model

Geoscientific Model Development Discussions ◽

10.5194/gmdd-7-3441-2014 ◽

2014 ◽

Vol 7 (3) ◽

pp. 3441-3480 ◽

Cited By ~ 8

Author(s):

R. Briant ◽

L. Menut ◽

G. Siour ◽

C. Prigent

Keyword(s):

Air Quality ◽

Main Part ◽

Roughness Length ◽

Mineral Dust ◽

Satellite Observations ◽

Production Model ◽

Dust Production ◽

Dust Emissions ◽

Sahel Region ◽

Agricultural Areas

Abstract. In the region including Africa and Europe, the main part of mineral dust emissions is observed in Africa. The particles are thus transported towards Europe and constitute a non-negligible part of the surface aerosols measured and controlled in the framework of the European air quality legislation. The modelling of these African dust emissions fluxes and transport is widely studied and complex parameterizations are already used in regional to global model for this Sahara-Sahel region. In a lesser extent, mineral dust emissions occur locally in Europe, mainly over agricultural areas. Their modelling is generally poorly done or just ignored. But in some cases, this contribution may be important and may impact the European air quality budget. In this study, we propose an homogeneized calculations of mineral dust fluxes for Europe and Africa. For that, we extended the CHIMERE dust production model (DPM) by using new soil and surface datasets, and the global aeolian roughness length dataset provided by GARLAP from microwave and visible satellite observations. This DPM is detailed along with academic tests case results and simulation on a real case results.

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Impact of dust size parameterizations on aerosol burden and radiative forcing in RegCM4

Atmospheric Chemistry and Physics ◽

10.5194/acp-17-769-2017 ◽

2017 ◽

Vol 17 (2) ◽

pp. 769-791 ◽

Cited By ~ 7

Author(s):

Athanasios Tsikerdekis ◽

Prodromos Zanis ◽

Allison L. Steiner ◽

Fabien Solmon ◽

Vassilis Amiridis ◽

...

Keyword(s):

Optical Depth ◽

Radiative Forcing ◽

Climate Model ◽

Size Range ◽

Regional Climate ◽

Deposition Velocity ◽

Research Unit ◽

Dust Particles ◽

Total Size ◽

The Mediterranean

Abstract. We investigate the sensitivity of aerosol representation in the regional climate model RegCM4 for two dust parameterizations for the period 2007–2014 over the Sahara and the Mediterranean. We apply two discretization methods of the dust size distribution keeping the total mass constant: (1) the default RegCM4 4-bin approach, where the size range of each bin is calculated using an equal, logarithmic separation of the total size range of dust, using the diameter of dust particles, and (2) a newly implemented 12-bin approach with each bin defined according to an isogradient method where the size ranges are dependent on the dry deposition velocity of dust particles. Increasing the number of transported dust size bins theoretically improves the representation of the physical properties of dust particles within the same size bin. Thus, more size bins improve the simulation of atmospheric processes. The radiative effects of dust over the area are discussed and evaluated with the CALIPSO dust optical depth (DOD). This study is among the first studies evaluating the vertical profile of simulated dust with a pure dust product. Reanalysis winds from ERA-Interim and the total precipitation flux from the Climate Research Unit (CRU) observational gridded database are used to evaluate and explain the discrepancies between model and observations. The new dust binning approach increases the dust column burden by 4 and 3 % for fine and coarse particles, respectively, which increases DOD by 10 % over the desert and the Mediterranean. Consequently, negative shortwave radiative forcing (RF) is enhanced by more than 10 % at the top of the atmosphere and by 1 to 5 % on the surface. Positive longwave RF locally increases by more than 0.1 W m−2 in a large portion of the Sahara, the northern part of the Arabian Peninsula and the Middle East. The four-bin isolog method is to some extent numerically efficient, nevertheless our work highlights that the simplified representation of the four-bin approach produces less dust optical depth and RF, a fact that should be taken into account by future studies of the same region.

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