Displays

Mineral dust accumulation is often causally associated with aridity, with higher dust deposition rates are assumed to reflect increasing magnitude of aridity. However, the relation between dust deposition and aridity is not straightforward; grain sizes play a crucial role in processes associated with mineral dust generation, transportation and deposition in sedimentary settings.

In this study, we apply grain-size analyses in six well-studied cores (spanning the late Holocene) previously collected from alpine lake sites distributed across the arid and semi-arid regions of west, southwest, and the Great Plains of North America. Previous work with these cores has demonstrated that the lake sediments are predominantly detrital, windblown particles and little to no impact of fluvial proceeses . We find that the most commonly occurring grain sizes are a fine fraction (typically <4 microns, which is easily lofted and transported long distances) and a coarse fraction (typically >25 microns and in some cases with a distinct peak at 100 microns, both of which are are too large to be carried long distances and suggest short distance transportation). We used grain size separation techniques to separate the two size fractions and geochemically fingerprinted those from three sites.

We find that more rapid accumulation of the coarser coarser-grain size fractions occurred during wetter intervals in the Holocene. Furthermore, the geochemistry of the coarse fractions indicates regional rather than local sourcing of the material from bedrock weathering. We do not find any clear relationships between the fine fraction and aridity patterns, nor a clear source region for this material.

We hypothesize that the increase in coarser dust deposition during wetter intervals is related to either intensification of land-use patterns associated with agriculture and/or to episodically strong winds. Warmer and wetter intervals in the areas under consideration have been associated with intensified cyclogenesis. Our study demonstrates the critical need to incorporate grain-size analysis as well as geochemical fingerprinting of the different size fractions in interpreting mineral dust record.

Acknowledgement: James Sickman, Jason Neff (for sharing samples), Jacob Ashford, Tyler Vollmer, Audriana Pollen, Alejandra Pedrazza, (for assistance with analyses and archival visits), John Morton, Wendy Freeman (for assisting students in the laboratory), Aradhna Tripati and Juan Lora (for assisting with data interpretation).

How to cite: Bhattacharya, A., Bennett, A., Marchitto, T., and Leithold, E.: Coarse-grained mineral dust deposition in alpine lakes provide evidence of increased windspeeds associated with more intense cyclogenesis during warmer intervals of the late Holocene period in arid and semi-arid tracts of North America., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-190, https://doi.org/10.5194/egusphere-egu2020-190, 2020.

A three-month experiment (June-August 2019) had been carried out on the undulating terrain of the Taklimakan Desert. The mass concentration characteristics of PM_2.5 and PM₁₀ at different locations of the sand ridge were obtained, studying the correlation between dust aerosol mass concentration and meteorological factors under different weather conditions. The results show that: (1) There are differences about the concentration of PM_2.5 and PM₁₀ in different locations of sand ridges under different typical weather conditions. The average mass concentration of PM_2.5 on sunny days meets: West Low Site > East Low Site > High Site, According to the dynamic  characteristic of PM₁₀, peak-valley value of the three stations fluctuated sharply, and the daily average value of mass concentration shows: High Site > East Low Site > West Low Site. When the sand blowing and floating weather occurred, the variation of PM_2.5 mass concentration meet the following rule: East Low Site > High Site, PM₁₀ shows the opposite law. When the first sandstorm occurs, the PM_2.5 mass concentration satisfies the following Law: West Low Site 10 mass concentration change is generally expressed as: West Low Site 2.5 and PM₁₀ meets: West Low Site> High Site> East Low Site (2) Sunny Temperature、 Atmospheric Pressure, Relative Humidity of east low site, high site have a close correlation with PM_2.5, PM₁₀ Mass Concentrations, the wind speed of the west low site and the high site was significantly correlated with the PM_2.5 and PM₁₀ mass concentrations. When the dusty weather occurs, the wind speed has a significant effect on the mass concentration of dust aerosol in the high site, and there is a significant positive correlation between the atmospheric pressure and the aerosol mass concentration in the east low site or high site. During the sand-dust weather , the PM_2.5 and PM₁₀ mass concentrations were significantly negatively correlated with the atmospheric pressure in the high sand dunes, the correlation between wind speed and the PM_2.5 and PM₁₀ mass concentrations was greater than the East low Site. During the sandstorm, atmospheric pressure and temperature have a significant effect on the mass concentration of PM_2.5 and PM_10.

How to cite: He, Q. and Zhao, Q.: Analysis on mass concentration of dust aerosols in rough terrains of the Taklimakan Desert Hinterland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1512, https://doi.org/10.5194/egusphere-egu2020-1512, 2020.

The breakdown of nocturnal low-level jets (NLLJs), West African heat low (WAHL), and Harmattan Surges (HS) have been proved to be important meteorological drivers of the seasonal variation of dust emissions over North Africa. This study further investigated their relative contributions to the interannual variation of dust emissions from 1980 to 2018. Dust emissions from the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2), precipitation data from TerraClimate, and wind speed, temperature, and geopotential from the European Centre for Medium-Range Weather Forecasts (ECMWF) were used to examine the roles of precipitation and wind speed in the dust emission trend as well as the spatiotemporal characteristics of the contributions of those three meteorological factors to the interannual variation of dust emissions. Results indicated that the dust emissions over Sahel and the southern coast of Mediterranean were more sensitive to precipitation rather than wind speed, while areas that were not influenced by rainfall were highly correlated with the cube of the wind speed at 10 m above surface with p < 0.001. The regional difference in the contribution of the three meteorological factors was significant. HS was the main contributor for dust emissions over the northern North Africa primarily in winter and spring. NLLJs primarily controlled the southern part (south of 20°N) in almost all seasons especially in winter and spring, while they contributed more to dust emissions north of 20° N from June to August. The contribution of WAHL started from the south of the Hoggar-Tibesti channel and the lee of Ethiopian Highlands in winter, then it moved northwestward in spring and reached their strongest states in summer.

How to cite: Shi, L., Zhang, J., Yao, F., and Zhang, D.: Relative importance of three climate factors on dust emissions over North Africa, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9181, https://doi.org/10.5194/egusphere-egu2020-9181, 2020.

Identifying the provenance of mineral dust depositions in Antarctica is crucial to reconstruct Southern Hemisphere (SH) atmospheric circulation, validate numerical models, evaluate their contribution as micronutrients in the Southern Ocean and assess their control on the climate changes. For the last few decades, it has been demonstrated Southern South America (SSA) is the main precursor of dust reaching Antarctica during both ice ages and interglacial periods (e.g. Gili et al., 2017, 2016). However, the origin of modern dust depositions on the Antarctic continent is still poorly constrained. Back in the nineties, together with SSA, Australia, New Zealand, and Southern Africa were firstly identified as dust contributors to East Antarctica (EA) (e.g. Delmonte et al., 2004a). Since then, only SSA and Australian dust sources benefited from detailed studies. While some works identified the Makgadikgadi and Etosha Pans as southern Africa's major mineral dust sources in the SH, it was not until recently the Namib Desert coastal areas were described as another important regional dust sources. Within the Namib Desert and along the coast, the Kuiseb (K), Omaruru (O) and Huab (H) dry riverbeds are the three main areas identified as the dustiest ones with the higher frequency of dust emission events (Von Holdt et al., 2017). Here we use Sr, Nd and Pb isotopes (measured on HR-MC-ICP-MS) to characterize and evaluate the influence of this region in Southern Africa as a dust source to EA. Samples collected in K, O and H desertic areas were analyzed together with snow samples collected along a ~250 km N-S transect (defined from the coast to inland) at seven different sampling sites in the surroundings of Dronning Maud Land, EA. In addition, using the bulk of the Huab region, dust aerosols were generated into an atmospheric simulation chamber (CESAM) to reproduce, mechanically the saltation and sandblasting processes responsible for the release of mineral dust in natural conditions. Our isotopic results show Namibia’s coast emerged as another possible source end-member, together with some regions in SSA, that supply dust to EA during warmer periods.

References:

Delmonte, B., Basile-Doelsch, I., Petit, J.R., Maggi, V., Revel-Rolland, M., Michard, A., Jagoutz, E., Grousset, F., 2004. Comparing the EPICA and Vostok dust records during the last 220,000 years: stratigraphical correlation and provenance in glacial periods. Earth-Sci. Rev. 66, 63–87.

Gili, S., Gaiero, D.M., Goldstein, S.L., Chemale, F. Jr., Koester, E., Jweda, J., Vallelonga, P., Kaplan, M.R., 2016. Provenance of dust to Antarctica: a lead isotopic perspective. Geophys. Res. Lett. 43. http://dx.doi.org/10.1002/2016GL068244.

Gili, S., D.M. Gaiero, S.L. Goldstein, F. Chemale, J. Jweda, M.R. Kaplan, R.A. Becchio, and E. Koester (2017). Glacial/interglacial changes of Southern Hemisphere wind circulation from the geochemistry of South American dust. Earth Planet. Sci. Lett., 469, 98-109, doi: 10.1016/j.epsl.2017.04.007.

Von Holdt, JR., Eckardt FD., and Wiggs GFS., 2017. Landsat identifies aeolian dust emission dynamics at the landform scale. Remote Sensing of Environment 198., 229–243.

How to cite: Gili, S., Vanderstraeten, A., Cazaunau, M., Chaput, A., Doussin, J.-F., Di Biagio, C., Formenti, P., King, J. S., Magnold, A., Mattielli, N., Pangui, E., Van Overmeiren, P., and Walgraeve, C.: The role of Southern Africa as a dust precursor to East Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18441, https://doi.org/10.5194/egusphere-egu2020-18441, 2020.

Throughout the Quaternary, variations of the insolation received over Africa have governed the monsoon dynamics in this region, generating a recurrence of intense rainfall periods. These African Humid Periods (AHP) are characterized by a major transformation of the Saharan hydrological cycle, favouring the development of vast fluvial systems and tropical humid ecosystems in the currently hyper-arid Sahara Desert. In the current context of global warming, the mechanisms as well as the environmental responses associated with these periods of rapid changes between two extreme climatic contexts remain crucial to understand. Many studies have investigated the mechanisms associated with the last AHP that occurred in the early Holocene (9 to 5ka), and more particularly its initiation and termination. Despite all these efforts, these climatic transitions remain highly debated (e.g. influence of high latitudes versus regional forcing, vegetation feedback). Here, we propose to improve our understanding of the Holocene AHP by studying Saharan dust deposited in Lake Bastani (Corsica, western Mediterranean) during the last 12ka. Indeed, as dust emissions are function of the aridity of their sources, among other parameters such as wind intensity, Saharan dust fluxes recorded over and out of Africa may represent an indirect way to reconstruct Sahara past hydrological changes. Bastani Lake is a high elevation system with a very restricted watershed and has been described as a natural Saharan dust trap during the last 3ka (Sabatier et al., accepted). In this study, we present a Holocene multi-proxy characterization of the fine-grained sediments recorded in Bastani lake. We develop a multiproxies approach based on mineralogy and major elements composition of the clay fraction as well as microscopic observations and quantification of the biogenic silica, which complicates Saharan dust supply estimation in this system. This effort to decipher the Bastani lake sediments composition will allow us to qualify and quantify the Saharan dust signal from the bulk sediment record (watershed erosion/alteration, biogenic silica productivity) in order to discuss, to our knowledge, the northernmost aeolian response of the Sahara desert hydrological changes of the termination of this key climatic transition.

Reference: Sabatier et al., Past African dust inputs in Western Mediterranean area controlled by the complex interaction between ITCZ, NAO and TSI, Climate of the Past, accepted.

Keywords: Saharan dust, Saharan hydrological cycle, Paleoclimatology, Holocene, clay mineralogy, geochemistry, biogenic silica.

How to cite: Leblanc, M., Skonieczny, C., Sabatier, P., Colin, C., Miska, S., Govin, A., Bout-Roumazeilles, V., Bory, A., Debret, M., Jouffroy-Bapicot, I., and Vannière, B.: Saharan dust deposited in Lake Bastani, Corsica: The northernmost dust record of the termination of the Holocene African Humid Period?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19212, https://doi.org/10.5194/egusphere-egu2020-19212, 2020.

Mineral dust plays an important role in the ocean’s carbon cycle through the input of nutrients and metals which potentially fertilise phytoplankton, and by ballasting organic matter from the surface ocean to the deep sea floor. In addition, mineral dust feeds back on climate through many different pathways like changing the radiative balance of the atmosphere, by stimulating cloud formation, dampening hurricane formation and by changing the earth’s albedo. Because open-ocean dust-flux measurements are either based on shipboard- or sediment-trap data, they are biased by interpolation and extrapolation of point observations in space and time. Alternatively, dust-flux estimations can be made using satellite observations, but these are often hampered by the presence of clouds. For these reasons we have been studying Saharan dust along a Transatlantic transect between northwest Africa and the Caribbean, focussing on temporal and spatial variability of dust-deposition fluxes and how these are reflected in terms of dust particle size and composition. One important finding deals with the deposition of Saharan dust by rain, which seems to be an important way to make nutrients available to phytoplankton living in the surface ocean. Nutrient-release bottle experiments in ambient sea water carried out along the same transect demonstrate how wet deposition of Saharan dust increases the release of both macro- (P, Si) and micronutrients (Fe) up to an order-of-magnitude as opposed to dry deposition. Rain-amplified bioavailability of these nutrients may well be the key to increased surface-ocean productivity in the remote and oligotrophic parts of the oceans and, potentially, also continental ecosystems. See: www.nioz.nl/dust

How to cite: Stuut, J.-B., Guerreiro, C., Brummer, G.-J., Korte, L., and Van der Does, M.: Present-day Saharan dust fluxes across the Atlantic Ocean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19416, https://doi.org/10.5194/egusphere-egu2020-19416, 2020.

Saharan dust events were investigated in the Carpathian Basin (Central Europe) for the period between 1979 and 2018 by using various satellite (TOMS and OMI Aerosol Index; MODIS AOD) and numerical forecast (Barcelona Supercomputing Centre’s DREAM, NMMB/BSC-Dust-model and SKIRON) products and modelled deposition of NASA’s Modern-Era Retrospective analysis for Research and Applications, Version 2. The identified 218 episodes were classified into three characteristic clusters based on synoptic background. 700 hPa geopotential height, wind vectors and meridional flow patterns, as well as backward trajectories of the episodes determined the classification.

Interannual variability of dust activity was remarkable, while seasonal frequencies of the episodes revealed clear spatiotemporal patterns with spring (40.2%) and summer (31.6%) maxima of the events. Mean values of dust deposition showed springtime maxima (44.1%) and dominance of wet deposition (77-93%), while amount of deposited dust material in the other seasons were quite similar, indicating the governing role of local weather conditions (e.g., precipitation patterns). Average warm advection of the episodes was 3.5°C (with spring minima, due to the more rain), but the decadal surface air temperature anomalies showed a general increasing trend.

Recently, a few more intense wintertime dust deposition events indicated changes in the deterministic atmospheric flow system. Seasonal and decadal zonal mean surface air temperature anomalies of dusty days showed clearly the increased warming of high latitudes during the last few winter episodes. The enhanced meridionality of (dust transporting) winds was also observable in the number of days with 15< m/s meridional wind component (at 700 hPa). Warmer Arctic region and more meandering air flow patterns could be responsible for these unusual dust episodes in the recent years.

Support of the National Research, Development and Innovation Office NKFIH KH130337 and NKFIH K120213 are gratefully acknowledged.

How to cite: Varga, G., Gammoudi, N., and Kovács, J.: 40-years of Saharan dust events in the Carpathian Basin: background, frequency, intensity, changing patterns, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20517, https://doi.org/10.5194/egusphere-egu2020-20517, 2020.

Aerosols, due to their interaction primary with the shortwave, but also with the longwave radiation, constitute a significant climate component, and at the same time an important, but still uncertain, factor of the contemporary climatic change. Apart from radiation, aerosols also interact with clouds, acting as Cloud Condensation Nuclei (CCN) and/or Ice Nuclei (IN), modifying the cloud optical and physical properties like cloud albedo, extent, lifetime or precipitation producing ability. Hence, it is also expected that high loads of specific aerosol types, such as desert dust, can induce even stronger effects on the above mentioned cloud properties.

More specifically, dust aerosols, which are inserted in the atmosphere mainly from the great world deserts, represent the major global aerosol component. These aerosols can remain suspended in the air and travel for several days, reaching areas far away from their sources. The Mediterranean Basin (MB), which is one of the most responsive regions to climate change, due to its location (nearby the Sahara desert in North Africa and the deserts of Middle East), is frequently affected from massive and extended dust transport. Because of the potentially significant role of these dust episodes, and their seasonal and inter-annual variability, they are worth to be studied and monitored through time.

In the present study, a modified version of a satellite algorithm, which is fully described by Gavrouzou et al. in another study of this conference, is used for the determination of strong and extreme dust episodes in the Mediterranean Basin over the period 2005-2018. The algorithm, using MODIS C6.1 spectral Aerosol Optical Depth (AOD) and OMI OMAERUV Aerosol Index (AI) as input data, ran on a daily and an 1°x1° pixel level basis and determined the occurrence and intensity of dust episodes whenever the AI is greater than 1 and the Angstrom Exponent (AE), which is calculated from spectral AOD data, is lower than 0.4. Any day is characterized as an episodic one when the dust optical depth (DOD) exceeds a computed threshold value (mean value plus two or four standard deviations for strong and extreme episodes, respectively) on at least 30 pixels of the study area. According to the algorithm results, 148 dust episode days (104 strong and 44 extreme) are found during the 2005-2018 period in the Mediterranean Basin. Most of the episodes occur in July (27 strong- and 3 extreme-episode days) and April (25 strong- and 6 extreme-episode days) while dust episodes are not detected at all in November and December. It is also found that in April, March and May take place the highest number of extreme MB episodes (23 out of the total 44 ones).

How to cite: Hatzianastassiou, N., Gavrouzou, M., Gkikas, A., and Mihalopoulos, N.: A climatology of dust episodes in the broader Mediterranean Basin using satellite MODIS C6.1 and OMI OMAERUV data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20288, https://doi.org/10.5194/egusphere-egu2020-20288, 2020.

Aerosol particles influence the Earth’s radiation budget, and thus weather and climate, through their interaction primarily with solar, but also with terrestrial radiation. Moreover, aerosol-cloud interactions are essential, since aerosols act as Cloud Condensation Nuclei (CCN) and/or Ice Nuclei (IN), and thus crucially affect cloud properties. Dust is a major aerosol type, accounting for a great fraction of the global aerosol mass, mostly originating from the global deserts). Dust aerosols exert a strong radiative forcing, while acting as CCN and/or IN, thus modifying the cloud physical optical and radiative properties as well as also cloud lifetime and precipitation. However, the direct and indirect effects of dust are strongly dependent on their spatial and temporal distribution, which still has a considerable degree of uncertainty. This uncertainty is due to limitations of our knowledge about the dust spatiotemporal variability, which is due to the strong variability both of the dust sources and emissions as well as their transport and removal processes. However, in the last two decades, significant steps have been made towards improving the ability to observe dust from satellites. Advanced retrieval algorithms enable to effectively derive key aerosol optical properties which are characteristic of their physical properties such as size and absorptivity. The availability of such aerosol data since the early 2000s offers nowadays the possibility to build satellite-based dust climatologies.

In the present study a global dust climatology is constructed using a satellite based algorithm. The algorithm is initialized with the latest editions of Collection 6.1 MODIS-Aqua and OMAER-UV OMI-Aura data spanning the 14-year period from 2005 to 2018. The raw data of the algorithm are: (1) spectrally resolved MODIS Aerosol Optical Depth-AOD and (2) OMI Aerosol Index-AI), both available on a daily basis and at 1°x1° latitude-longitude spatial resolution. The algorithm computes, using the spectral AOD values, the aerosol Angstrom Exponent (AE), which is finally used along with AI as the main algorithm input data that are characteristic of aerosol size (AE) and absorptivity (AI). By applying appropriate thresholds that ensure the coarse size and significant absorptivity of dust, the algorithm identifies presence of dust in the atmospheric column on a daily and 1°x1° basis over the entire globe and the period 2005-2018. The algorithm estimates the frequency of presence and the associated loading (in terms of dust optical depth, DOD) of dust on a monthly and annual basis. The 14-year study period enables the computation of climatological mean values, as well as the intra-annual and inter-annual variability and trends of dust. Specific emphasis is given to the world’s great deserts, as well as to regions undergoing important transport of dust.

How to cite: Gavrouzou, M., Hatzianastassiou, N., Gkikas, A., and Mihalopoulos, N.: Global dust climatology based on MODIS C6.1 and OMI-OMAERUV satellite data for the period 2005 to 2019, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-706, https://doi.org/10.5194/egusphere-egu2020-706, 2020.

An advanced dust reanalysis with high spatial (at 10km x 10km) and temporal resolution is produced in the framework of DustClim project (Dust Storms Assessment for the development of user-oriented Climate Services in Northern Africa, Middle East and Europe) [1], aiming to provide reliable information on dust storms current conditions and predictions, focusing on the dust impacts on various socio-economic sectors.

This regional reanalysis is based on the assimilation of dust-related satellite observations from MODIS instrument [2], in the Multiscale Online Nonhydrostatic Atmosphere Chemistry model (NMMB-MONARCH) [3], over the region of Northern Africa, Middle East and Europe. The reanalysis is now available for a seven-year period (2011-2016) providing the following dust products: Columnar and surface concentration, distributed in 8 dust particle size bins, with effective radius ranging from 0,15μm to 7,1μm, dust load, dry and wet dust deposition, dust optical depth (DOD) and coarse dust optical depth (radius>1μm) at 550nm and profiles of dust extinction coefficient at 550nm.

A thorough evaluation of the reanalysis is in progress to assess the quality and uncertainty of the dust simulations, using dust-filtered products, retrieved from different measurement techniques, both from in-situ and remote sensing observations. The datasets considered for the DustClim reanalysis evaluation, provide observations of variables that are included in the model simulations. The DOD is provided by AERONET network [4] and by IASI [5], POLDER [6], MISR [7] and MODIS space-borne sensors; Dust extinction profiles are provided by ACTRIS/EARLINET network [8] and CALIPSO/LIVAS dataset [9]; Dust PM10 surface concentrations derived from INDAAF/SDT [10] network and estimated from PM10 measurements [11] performed within EEA/EIONET [12] network; Dust deposition measurements collected by the INDAAF/SDT and the CARAGA/DEMO [13] networks; Dust size distribution from in situ observations (ground-based and airborne); And column-averaged dust size distribution at selected stations from the AERONET network.

In this work, we present the results of the model evaluation for the year 2012. The first evaluation results will focus on dust extinction coefficient profiles from EARLINET and LIVAS, on DOD using AERONET, MISR and MODIS datasets, and on dust PM10 concentration from INDAAF/SDT network. Moreover, a DOD climatology covering the whole reanalysis period (2011-2016) will be compared with the results obtained from AERONET network.

References

[1] https://sds-was.aemet.es/projects-research/dustclim

[2] https://modis.gsfc.nasa.gov/

[3] Di Tomaso et al., Geosci. Model Dev., 10, 1107-1129, doi:10.5194/gmd-10-1107-2017., 2017.

[4] https://aeronet.gsfc.nasa.gov/

[5] Cuesta et al., J. Geophys. Res., 120, 7099-7127, 2015.

[6] http://www.icare.univ-lille1.fr/parasol/overview/

[7] https://misr.jpl.nasa.gov/

[8] https://www.earlinet.org/

[9] Marinou et al., Atmos. Chem. Phys., 17, 5893–5919, https://doi.org/10.5194/acp-17-5893-2017, 2017.

[10] https://indaaf.obs-mip.fr/

[11] Barnaba et al., Atmospheric environment, 161, 288-305, 2017.

[12] https://www.eionet.europa.eu/

[13] Laurent et al., Atmos. Meas. Tech., 8, 2801–2811, 2015.

Acknowledgement

DustClim project is part of ERA4CS, an ERA-NET initiated by JPI Climate, and funded by FORMAS (SE), DLR (DE), BMWFW (AT), IFD (DK), MINECO (ES), ANR (FR) with co-funding by the European Union (Grant 690462).

How to cite: Mytilinaios, M., Mona, L., Barnaba, F., Ciamprone, S., Trippetta, S., Papagiannopoulos, N., Basart, S., Di Tomaso, E., Jorba, O., García-Pando, C. P., Proestakis, E., Marinou, E., Amiridis, V., Formenti, P., Cuesta, J., Di Biagio, C., Laurent, B., and Marticorena, B.: Evaluation of NMMB-MONARCH dust reanalysis within the DustClim ERA4CS project, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21863, https://doi.org/10.5194/egusphere-egu2020-21863, 2020.

DustClim (Dust Storms Assessment for the development of user-oriented Climate Services in Northern Africa, Middle East and Europe) is a project of the European Research Area For Climate Services (ERA4CS). DustClim is aiming to provide reliable information on sand and dust storms for developing dust-related services for selected socio-economic sectors: air quality, aviation and solar energy.

This contribution will describe the work done within the DustClim project towards the production of a dust reanalysis over the domain of Northern Africa, the Middle East and Europe at an unprecedented high spatial resolution (at 10km x 10km) using the state-of-art Multiscale Online Nonhydrostatic Atmosphere Chemistry model (MONARCH) and its data assimilation capability (Di Tomaso et al., 2017). An ensemble-based Kalman filter (namely the local ensemble transform Kalman filter – LETKF) has been utilized to optimally combine model simulations and satellite retrievals.

Dust ensemble forecasts are used to estimate flow-dependent forecast uncertainty, which is used by the data assimilation scheme to optimally combine model prior information with satellite retrievals. Satellite observations from MODIS Deep Blue with specific observational constraint for dust (Ginoux et al., 2012; Pu and Ginoux, 2016; Sayer et al., 2014) are considered for assimilation over land surfaces, including source regions. MONARCH ensemble has been generated by applying multi-parameters, multi-physics, multi-meteorological initial and boundary conditions perturbations. Sensitive parameters of the assimilation configuration like the balance between observational and background uncertainty, or the spatial location of errors have been carefully calibrated.

The dust reanalysis for the period 2011-2016 is being compared against independent dust-filtered observations from AERONET (AErosol RObotic NETwork) show the benefit of the assimilation of dust-related MODIS Deep Blue products over areas not easily covered by other observational datasets. Particularly relevant is the improvement of the model skills over the Sahara.

References:
Di Tomaso, E., Schutgens, N. A. J., Jorba, O., and Pérez García-Pando, C. (2017): Assimilation of MODIS Dark Target and Deep Blue observations in the dust aerosol component of NMMB-MONARCH version 1.0, Geosci. Model Dev., 10, 1107-1129, doi:10.5194/gmd-10-1107-2017.
Ginoux, P., Prospero, J. M., Gill, T. E., Hsu, N. C. and Zhao, M. Global-Scale Attribution of Anthropogenic and Natural Dust Sources and Their Emission Rates Based on Modis Deep Blue Aerosol Products. Rev Geophys 50, doi:10.1029/2012rg000388 (2012).
Pu, B., and Ginoux, P. (2016). The impact of the Pacific Decadal Oscillation on springtime dust activity in Syria. Atmospheric Chemistry and Physics, 16(21), 13431-13448.
Sayer, A. M., Munchak, L. A., Hsu, N. C., Levy, R. C., Bettenhausen, C., and Jeong, M.-J.: MODIS Collection 6 aerosol products: Comparison between Aqua’s e-Deep Blue, Dark Target, and “merged” data sets, and usage recommendations, J. Geophys. Res.-Atmos., 119, 13965–13989, doi:10.1002/2014JD022453, 2014.

Acknowledgement
DustClim project is part of ERA4CS, an ERA-NET initiated by JPI Climate, and funded by FORMAS (SE), DLR (DE), BMWFW (AT), IFD (DK), MINECO (ES), ANR (FR) with co-funding by the European Union (Grant 690462). We acknowledge PRACE for awarding access to HPC resources through the eDUST and eFRAGMENT1 projects.

How to cite: Di Tomaso, E., Basart, S., Escribano, J., Ginoux, P., Jorba, O., Macchia, F., Montane, G., Castrillo, M., and Pérez García-Pando, C.: Towards high-towards high-resolution dust reanalysis for Northern Africa, the Middle East and Europe, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17599, https://doi.org/10.5194/egusphere-egu2020-17599, 2020.

How to cite: Wang, X. and Liu, J.: Impact of Arctic amplification on declining spring dust events in East Asia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8175, https://doi.org/10.5194/egusphere-egu2020-8175, 2020.

In this study, we present results of new mineral dust simulations performed with the model setup ECHAM-HAMMOZ. The simulations are part of the AWI project DustIron, a coupled data-model approach to investigate past changes of the Southern Hemisphere dust cycle and potential Southern Ocean iron fertilization as a result of atmospheric mineral dust / iron input.

The model setup consists of the latest atmospheric general circulation model release ECHAM6, coupled to the aerosol model HAM2.3 and the atmospheric chemistry model MOZ1.0. Our focus is on dust emission and deposition rates as well as the identification of key source and deposition areas in the Southern Hemisphere by sensitivity experiments for modern (1850 AD) and last glacial maximum (21 ka BP) climate conditions. The spatial patterns of the decadal mean of the simulated annual dust deposition agree well with recent CESM simulation results (Albani et al., 2016) for modern climate conditions. A comparison of the decadal mean of the total global annual dust emissions simulated with ECHAM-HAMMOZ (1361 Tg a^-1) to CESM (2785 Tg a^-1, Albani et al., 2019) shows that the model performs rather at the lower end concerning global dust emissions. The tendency to a slight underestimation of global annual mineral dust emissions, however, is in agreement with the model’s aerosol evaluation by Tegen et al. (2019).

How to cite: Krätschmer, S., Werner, M., Lamy, F., Völker, C., and van der Does, M.: DustIron: Global mineral dust simulations with ECHAM-HAMMOZ for modern and last glacial maximum climate conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5463, https://doi.org/10.5194/egusphere-egu2020-5463, 2020.

Since the late 20th century East Asia has frequently experienced unprecedented transboundary extreme ultrafine dust events (TEUDEs) due to a fast economic development based on significant amount of fossil fuel consumption. In this study, spatio-temporal patterns of the TEUDEs in East Asia and the roles of synoptic climate patterns and changing large-scale atmospheric circulation systems in exacerbating the anthropogenic atmospheric pollution events causing considerable human deaths are examined. Analyses of the Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua and Terra aerosol optical depth (AOD) data (2000-2019) clearly show that the pollutants are produced mainly in northern China and move toward central Korea and southern Japanese islands during cold seasons when coals consumption soars for heating. Synoptic climatic maps drawn from the NCEP-NCAR I reanalysis data for multiple TEUDEs demonstrate that a north clockwise- south anticlockwise wind vector anomaly pattern in cold seasons formed by less southward meandering of Siberian High pressure (SH) helps the stagnation of significant amount of ultrafine dusts over East Asia. It is also notable that the long-term poleward retreating trend of cold season circumpolar vortex, which is associated with less frequent gusty wind flow from the SH, may provide a favorable condition for intense, long-lasting TEUDEs across East Asia under a warmer monsoon climate.

How to cite: Choi, G.: Transboundary Extreme Ultrafine Dust Events in East Asia under a Warmer Monsoon Climate, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18811, https://doi.org/10.5194/egusphere-egu2020-18811, 2020.

An estimated 50 Mt yr^-1 of dust is emitted from North American landscapes, with profound regional impacts (Shao et al., 2011). Dust emission flux in North America is controlled by wind speed and land surface (aerodynamic) roughness that are variable in both space and time. Vegetation growth, form and spatial distribution characterise different ecosystem regimes and protect the soil surface from the shearing stress of the wind. In the dry western US, diverse land use and management drivers create disturbance regimes that produce diverse ecosystem responses that could be drastically impacting rates of wind erosion and dust emission (Ravi et al., 2010). Resolving the impacts of ecosystem change on aeolian processes is needed to quantify anthropogenic-induced dust loads and identify management options as environmental solutions (Webb and Pierre, 2018).

Currently, erosion surfaces in North America are derived from satellite imagery, either by spatial analysis of mean aerosol optical depth concentrations (e.g. Ginoux et al., 2012) or point source identification through subjective analysis of individual daily multispectral images (e.g. Lee et al., 2012; Kandakji et al., 2020). In either approach, the results are subjected to spatial and temporal bias caused by a lag in emission-to-observation period and loss of data during cloudy (dust and meteorological) periods. To complement these approaches we produced the first moderate (500 m) resolution daily maps of dust emission across the dry western United States. These maps were based on estimates of soil surface wind friction velocity (u_s*) derived from MODIS albedo data (Chappell and Webb 2016) using a commonly applied model (Marticorena and Bergammetti, 1995).

The North American dust emission climatology from 2001-2018 was compared with the u_s* data volume to identify the spatio-temporal occurrence of three key disturbance regimes: i) land clearing for energy infrastructure, ii) invasion of shrublands by exotic annual grasses that alter fire regimes, and iii) replacement of grasslands by invasive shrub species. Against this background we examine the state and transition of ecosystem change across these landscapes to understand the impact on current dust emission. We use these findings to comment on the implications for future dust emission and to encourage the development of this modelling approach in Earth System Models.    

How to cite: Hennen, M., Webb, N., and Chappell, A.: The impact of ecosystem change on dust emission in North America, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21883, https://doi.org/10.5194/egusphere-egu2020-21883, 2020.

With the advances in modeling approaches, and the application of satellite and ground-based data in dust-related research, our understanding of the dust cycle is significantly improved in recent decades. However, two aspects of the dust cycle, the vertical profiles and diurnal cycles of dust aerosols have not been understood adequately, mainly due to the sparsity of observations. A micro-pulse LIDAR has been operating at the King Abdullah University of Science and Technology (KAUST) campus located on the east coast of the Red Sea (22.3N, 39.1E), measuring the backscattering from atmospheric aerosols at a high temporal resolution for several years since 2015. It is the only operating LIDAR system over the Arabian Peninsula. We use this LIDAR data together with other collocated observations and high-resolution WRF-Chem model simulations to study the 3-d structure of aerosols, with a focus on dust over the Red Sea Arabian coastal plains. 

Firstly, we investigate the vertical profiles of aerosol extinction and concentration in terms of their seasonal and diurnal variability. Secondly, using the hourly model output and observations, we study the diurnal cycle of aerosols over the site. Thirdly, we explore the interactions between dust aerosols and land/sea breezes, which are the critical components of the local diurnal circulation in the region. 

We found a substantial variation in the vertical profile of aerosols in different seasons. There is also a marked difference in the daytime and nighttime vertical distribution of aerosols in the study site, as shown by LIDAR data. A prominent dust layer is observed at ~5-7km at night in the LIDAR data, corresponding to the long-range transported dust of non-local origin. The vertical profiles of aerosol extinction are consistently reproduced in LIDAR, MERRA-2 reanalysis, and CALIOP data, as well as in WRF-Chem simulations in all seasons. Our results show that the sea breezes are much deeper (~1km) than the land breezes (~200m), and both of them prominently affect the distribution of dust aerosols over the study site. Sea breezes mainly trap the dust aerosols near the coast, brought by the northeasterly trade winds from inland deserts, causing elevated dust maxima at the height of ~1.5km. Also, sea and land breezes intensify dust emissions from the coastal region in daytime and nighttime, respectively. Such dust emissions caused by sea breezes and land breezes are most active in spring and winter. Finally, WRF-Chem successfully captures the onset, demise, and the height of some large-scale dust events as compared to LIDAR data qualitatively. 

How to cite: Parajuli, S., Stenchikov, G., Ukhov, A., and Shevchenko, I.: Interaction of the Vertical Profile of Dust Aerosols with Land/sea Breezes over the Eastern Coast of the Red Sea from LIDAR and High-resolution WRF-Chem Simulations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2077, https://doi.org/10.5194/egusphere-egu2020-2077, 2020.

The Infrared Atmospheric Sounder Interferometer (IASI) is well suited for monitoring of dust aerosols because of its capability to determine both AOD and altitude of the dust layer, and because of the good match between the IASI times of observation (9.30 am and pm, local time) and the time of occurrence of the main Saharan dust uplift mechanisms. Here, starting from IASI-derived dust characteristics for an 11-year period, we assess the capability of IASI to bring realistic information on the dust diurnal cycle. We first show the morning and nighttime climatology of IASI-derived dust AOD for two major dust source regions of the Sahara: The Bodele Depression and the Adrar region. Compared with simulations from a high resolution model, permitting deep convection to be explicitly resolved, IASI performs well. In a second step, a Dust Emission Index specific to IASI is constructed, combining simultaneous information on dust AOD and mean altitude, with the aim of observing the main dust emission areas, daytime and nighttime. Comparisons are then made with other equivalent existing results derived from ground based or other satellite observations. Results demonstrate the capability of IASI to improve the documentation of dust distribution over Sahara over a long period of time. Associating observations of dust aerosols in the visible, on which a majority of aerosol studies are so far based, and in the infrared thus appears as a way to complement the results from other satellite instruments in view of improving our knowledge of their impact on climate.

How to cite: capelle, V., chedin, A., Scott, N., and Todd, M.: Contribution of IASI to the observation of the dust aerosol diurnal cycle over Sahara, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15180, https://doi.org/10.5194/egusphere-egu2020-15180, 2020.

The terrain surrounding the Sahara desert is formed by some mountains ranges, as the Atlas mountain system in the northern edge of the desert and the Hoggar Mountains in Southern Algeria. Such orography, jointly with atmospheric circulation, plays an important role in the mobilization and transport of desert dust over medium and large distances. This study explores the interaction between complex terrain and atmospheric circulation in order to better understand an exceptional desert dust outbreak affecting Portugal in February 2017. The Meso-NH model is able to represent the atmospheric motions in different scales, and has been implemented with a rather complete parametrization package of physical processes in the atmosphere. The capability of the model to simulate dust emission is also explored. The on-line dust emission parametrization type is taken from the distribution of emitted dust of SURFEX with no need to use chemistry to activate dusts. A set of two simulations was performed for the period between 16 February at 0000 UTC to 24 February 1200 UTC, with the Meso-NH model configured in a single domain at 10 km horizontal resolution and 300x360 grid points. The experiments were defined as a) control experiment (CTRL), and b) dust experiment (DUST). From the large domain simulations, it was possible to assess the source of dust and its mobilization over Western Sahara desert, namely over the Northern part of Mauritania and Mali and Eastern part of Algeria. The formation of a cyclonic circulation at the surface favoured the dust uplifting. Such a surface low merged with a cut-off low that moved southward over the Iberian Peninsula and remained centred in the north of Morocco. Such pattern intensified the northward flow found at 700 hPa toward the Atlas Mountains range, inducing the dust transport above 3 km altitude. As expected, the simulations showed the ability to assess important details about the atmospheric circulation not resolved by low density of observations over the domain considered. Furthermore, the simulations were able to show the way that the atmospheric ingredients were brought together to produce the exceptional transport of desert dust toward Portugal. The orographic effects playing an important role in dust mobilization (convergence and cyclogenesis at the surface) and atmospheric circulation to the maintenance of the dust transport have been highlighted. Such event were responsible for the transport of high amount of dust toward the Iberian Peninsula.

How to cite: Costa, M. J., Couto, F., Cardoso, E., Salgado, R., and Guerrero-Rascado, J. L.: Modelling an exceptional desert dust transport toward Portugal on February 2017, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11443, https://doi.org/10.5194/egusphere-egu2020-11443, 2020.

Aeolian dust, the most dominant atmospheric aerosol by mass, decreases the solar energy reaching the Earth surface by absorbing and scattering the solar radiation. This energy loss increases mainly with the dust concentration in the atmosphere, which is controlled by the emission, transport and removal of the dust particles. All these processes can vary significantly depending on the convection treatment in the model simulations, thereby affect the solar energy forecast.

This study investigates the dust impacts on solar energy generation within convection-resolving simulations using the next-generation atmospheric modeling system ICON-ART (ICOsahedral Nonhydrostatic with Aerosols and Reactive Trace gases). The simulation set-up includes a global domain with 40 km horizontal resolution with three nests down to 5 km horizontal resolution over North Africa and Europe. The innermost nest resolves convection while other domains are based on parameterized convection. This set-up is used to simulate the period 22-27 June 2019, which is associated with a Saharan dust outbreak in clear sky conditions over North Africa and large parts of Europe. 

Compared to the global simulation, the convection-resolving simulation leads to significantly higher dust optical depth in North Africa. This is related to the elevated coarse mode concentrations due to higher vertical velocities in the convection-resolving simulation. However, dust optical depth over Europe only slightly changes as a large portion of coarse mode particles do not reached Europe due to their large sedimentation velocities. The results are compared with AERONET, ceilometer and radiation measurements.

How to cite: Hoshyaripour, G. A., Bachmann, V., Filipitsch, F., Straub, J., Foerstner, J., Mattis, I., Wagner, F., Vogel, H., and Vogel, B.: Saharan Dust and Solar Energy Generation in Europe: Case Study of June 2019, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7330, https://doi.org/10.5194/egusphere-egu2020-7330, 2020.

In order to reveal the essential feature of radiation in extreme arid region of Northwest China,using the global radiation，direct radiation,diffuse radiation and meteorological data in the Tazhong station( in Takli-makan desert hinterland,83°39'E,38°58'N),the characteristics of atmospheric transparency coefficient,influence of sand-dust on solar radiation were analyzed by the statistical methods.The results show that: The coefficient of atmosphere transparency is better from October to December than other months,but it's worse in spring and summer.The index of the atmosphere transparency P₂ is the most ( least) in clear day ( sand storm day ) .The global radiation is more than 1000 W·m^-2 in clear day,dust day and sand blowing day,while,it is up to 700 W·m^-2 in sand storm day at most.The diffuse radiation is partly less than 400 W·m^-2,mainly between 100 and 200 W·m^-2in clear day.It is less than 600 W·m^-2 in dusty day mostly. The direct radiation is reduced by dust aerosol.The probability are 41.2%,72.5%,78.1% and 100% when direct radiation is less than 200 W·m^-2 during clear day,dust day,sand blowing day and sand storm day.The diffuse radiation is gradually concentration high value with the sand of the atmosphere is increased.The variation of every radiation is big in dusty day.The daily curve (value) of diffuse radiation is similar to the global radiation,which is reduced by dust aerosol is the same as the direct radiation.That suggests the atmosphere transparency is closely related to the global radiation,diffuse radiation and direct radiation.

How to cite: Jin, L., He, Q., Li, Z., Mamtimin, A., and Miao, Q.: Influence of Sand-Dust on Solar Radiation in the Hinterland of Taklimakan Desert, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1515, https://doi.org/10.5194/egusphere-egu2020-1515, 2020.

The interactions between aeolian dust and anthropogenic air pollution, notably chemical ageing of mineral dust and coagulation of dust and pollution particles, modify the atmospheric aerosol burden. Since the aerosol particles can act as cloud condensation nuclei, this not only affects the radiative transfer directly via aerosol radiation interactions, but also indirectly through cloud adjustments. We study both radiative effects using the global ECHAM/MESSy atmospheric chemistry-climate model (EMAC) which combines the Modular Earth Submodel System (MESSy) with the European Centre/Hamburg (ECHAM) climate model. Our simulations show that the dust-pollution interactions reduce the cloud water and hence the reflection of solar radiation. The associated climate warming outweighs the cooling which the dust-pollution interactions exert through the direct radiative effect. In total, this results in a net warming by dust-pollution interactions which we estimate to moderate the negative global anthropogenic aerosol forcing at the top of the atmosphere by more than 0.1 W / m².

How to cite: Klingmueller, K., Karydis, V., Bacer, S., Stenchikov, G., and Lelieveld, J.: Weaker cooling by aerosols due to dust-pollution interactions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8381, https://doi.org/10.5194/egusphere-egu2020-8381, 2020.

Desert dust aerosols occur as complex ensembles of particles with irregular shapes. Furthermore, these particles consist of a variety of different minerals which often coexist next to each other within individual particles. While in recent years the nonsphericity of particles is considered more and more in optical models of desert dust, the mineralogical inhomogeneity is still rarely considered though it can have a significant effect on light scattering and absorption.

Is this study, we discuss optical properties of irregularly-shaped inhomogeneous dust particles which were modelled with a Discrete Dipole Approximation code. We show how absorbing inclusions embedded in a non-absorbing material affect absorption and scattering by a particle as compared to the case when all the absorbing material is homogeneously distributed inside the particle. Hematite and goethite were selected as the material of the absorbing inclusions since these minerals are known to be responsible for most of the light absorption in desert dust aerosols.

How to cite: Gasteiger, J., Gattringer, A., and Weinzierl, B.: Model study on effect of hematite and goethite on optical properties of inhomogeneous desert dust aerosols, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18006, https://doi.org/10.5194/egusphere-egu2020-18006, 2020.

Natural mineral dust and intensive anthropogenic emissions and its complex mixing processes during transport result in great impacts on regional environmental quality and climate in East Asia. However, the morphology change and hygroscopicity of East Asian dust particles owing to coating anthropogenic pollutants are still statistically poorly understood. In this study, the statistically significant morphology change and hygroscopic growth of East Asian dust particles in a real atmosphere were firstly evaluated by combining CALIOP lidar measurements and relative humidity (RH) derived from the MERRA-2 during the past ten years (2007-2016). Our statistical results indicate that the optical properties of East Asian dust aerosol have significant region inhomogeneity and trend to be smaller in particle size and regular in shape during transport away from the source area. The dust particle irregularities and extinction coefficient were significantly decreasing and increasing with increasing ambient RH, respectively.The irregularity declining rate of mineral dust tended to slow down from source region (-0.89) to transport region with intensive anthropogenic emissions (-0.14). The strong positive linear correlation between dust extinction coefficient and relative humidity demonstrate the dust aerosol’s hygroscopic growth. It is attributed as a result of possible saline component and coating anthropogenic pollutants. The stronger hygroscopic growth of dust aerosol in the lower atmosphere has also been found. These results improve our understanding on the hygroscopicity of East Asian dust aerosol. Dust particles coating with anthropogenic pollution have a great ability of acting cloud condensation nucleus (CCN) in the lower atmosphere, which will affect the cloud microphysical processes and even climate effect.

How to cite: Wang, T. and Han, Y.: CALIPSO-based morphology change and hygroscopic growth of East Asian dust , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9312, https://doi.org/10.5194/egusphere-egu2020-9312, 2020.

Electrical processes can be a potential key player in the lifecycle of desert dust. The dust particles can be charged during their transport, either by the attachment of atmospheric ions or by particle to particle collisions (triboelectric effect). Measurements indicate that, on average, larger particles become positively charged while the smaller ones become negatively charged [Zhao, H. L., J. Electrostat, 55, 2002; Lacks, D.J., et al., Phys. Rev. Lett., 100, 188305, 2008; Merrison, J.P., Aeolian Res., 4, 2012; Shinbrot, T. and Herrmann, H.J., Nature, 451, 2008]. During dust transportation, the larger and mainly positively charged particles separate from the smaller negatively charged particles due to the gravitational sedimentation, which sorts the dust particles by size. This process develops vertical electric fields within the dust cloud, enhancing the pre-existing field due to the depletion of atmospheric conductivity by the presence of the dust layer [Gringel W. and Mulheisen. R., Beitr. Phys. Atmos., 51, 121–8, 1978]. Depending on its strength, the total electric field within the dust cloud can: (a) counteract the gravitational settling of large particles and (b) cause a preferential orientation of the non-spherical particles along the vertical direction affecting particle aerodynamics [Ulanowski, Z., et al., Atmos. Chem. Phys., 7, 2007]. Therefore, electrical processes may alter dust removal processes, and thus the evolution of particle size during transport, affecting dust-radiation-cloud interactions and the associated air quality [Sajani S.Z., et al., Occup. Environ. Med., 68(6), 2011], weather, and climate modeling [Mahowald, N., et al., Aeolian Res., 15, 2014].

In the present work, we have developed a novel 3D Cartesian time-dependent model that takes into account several atmospheric processes, such as: (i) the ionization due to the galactic cosmic rays radiation, (ii) the ion-ion recombination, and (iii) the ion attachment to non spherical dust particles.  The model is able to self-consistently calculate the time dynamics of the atmospheric conductivity, and the atmospheric electric field, under the presence of a distribution of stationary non spherical dust particles. Additionally, the total charge density, dust particle charge and dust particle orientation are also quantified. The new 3D electrification formalism allows the study of dust layers without imposing any symmetry and  is valid for layers with any horizontal and vertical extend, as opposed to 1D models which are valid when the horizontal extend is much larger than the vertical, or to 2D models which assume a symmetry in the shape of the dust layer. The results are compared, in the limiting case that the horizontal extend is much larger than the vertical one, with those obtained from 1D models found in the past literature [e.g. Zhou, L., Tinsley, B.A., Adv. Space Res. 50, 2012]. Moreover, the effect of the studied electrification process is assessed through a comparison with recent and unique electric field measurements within lofted dust layers, as performed with the use of novel low cost atmospheric electricity sensors in an experimental campaign of the D-TECT ERC project, in Cyprus the past November.

How to cite: Mallios, S., Daskalopoulou, V., Skoubris, E., Hloupis, G., Papaioannou, A., and Amiridis, V.: A 3D Time-Dependent Model for the Study of the Electrification of Non Spherical Dust Particles due to Ion Attachment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-857, https://doi.org/10.5194/egusphere-egu2020-857, 2020.

Sediment samples were collected from Morocco, Algeria and Tunisia (as possible source sediments) and from Hungary (2018 dust events), and analyzed with the following measurements: laser diffraction, X-ray powder diffraction, automated static image analysis, and scanning electron microscopy (SEM). Similarities were expected in the results of desert-originated samples and samples collected in Hungary. In order to identify the typical dust transportation routes and possible source areas, the backward trajectories were plotted using the NOAA HYSPLIT model [1].

According to particle size distribution results, active dust emission is taking place at the location of investigated desert samples, and the samples collected in Hungary can be the particles out-blown from the source areas. The evaluated mineralogical results show that every sample contains quartz and phyllosilicates. SEM micrographs and image analyses results assume that the samples collected in Hungary are from the same source area. Using HYSPLIT application, trajectories of two analyzed dust events reveal that one desert sample, as a possible source is excluded and that the two trajectories cross each other at a junction point above North Africa (depression area between the Hoggar Mts. and Tademaït). This point can be the sought possible source location. The results in this study are convenient with those founded by Blott et al. [2] and Ahmed et al. [3]

Acknowledgment

Support of the National Research, Development and Innovation Office NKFIH KH130337 and K120213 is gratefully acknowledged.

References

1. Draxler, RR, Rolph, GD. 2012. HYSPLIT (HYbrid Single‐Particle Lagrangian Integrated Trajectory) Model access via NOAA ARL READY Website. NOAA Air Resources Laboratory: Silver Spring, MD. http://ready.arl.noaa.gov/HYSPLIT.php, last accessed 2019/03/20.
2. Blott, S. J., Al-Dousari, A. M., Pye, K., Saye, S. E.: Three-dimensional characterization of sand grain shape and surface texture using a nitrogen gas adsorption technique. Journal of Sedimentary Research 74, 156–159‏ (2004).
3. Ahmed, M., Al-Dousari, N., Al-Dousari, A.: The role of dominant perennial native plant species in controlling the mobile sand encroachment and fallen dust problem in Kuwait. Arabian Journal of Geosciences 9, 134 (2016)

How to cite: Kovács, J., Gammoudi, N., Kovács, A., and Varga, G.: Saharan dust events in the Carpathian Basin (Central Europe) in 2018: provenance analyses by granulometry, XRD and SEM methods, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10111, https://doi.org/10.5194/egusphere-egu2020-10111, 2020.

The contemporary aeolian system is poorly understood due in part to a scarcity of direct measurements of modern dust deposition. The Uinta Mountains of Northeastern Utah, USA are well-suited to the study of contemporary dust owing to their gently sloping, soil-mantled alpine zones and relatively inert, quartzite-dominated bedrock. Capitalizing on this unique setting, eight marble dust traps, as well as one active dust collector, have been installed throughout the mountain range. Previous study of samples from these collectors has supported the quantification of mineral dust inputs to alpine pedogenesis and identified isotopic fingerprints that link dust to potential source regions. This project focuses on dust emptied from these samplers in Fall 2019, representing two years of continuous dust accumulation. The mean dust flux for these years is 4.1 g/m²/y, which corresponds to historic flux measurements ranging from 2.7 g/m²/y to 4.4 g/m²/y. The relatively large dust mass of these multi-year samples allows for samples from each collector to be split into a coarse and fine fraction prior to further analysis. Before separation, the median grain size of 2019 dust samples is approximately 10 µm. After sample separation, carried out through timed settling following Stoke’s Law, the approximate median particle diameter is 6 µm for the fine fraction, and 20 µm for the coarse fraction. Coarse Uinta dust is more enriched in quartz and feldspar relative to fine dust, which is dominated by clay minerals. The coarse material is therefore more mineralogically similar to local bedrock, supporting the theory that larger particles are endogenous in origin. Clay minerals are less abundant in local bedrock, suggesting that fine mineral dust may have an exogenous source. Analysis of trace and major elemental abundances, as well as Sr and Nd isotopic fingerprinting will support additional interpretations about the nature and origin of modern dust in the Uintas. These results will contribute to ongoing efforts to better understand how specific dust source regions influence the properties of mineral aerosols arriving in remote alpine environments.

How to cite: Olson, P. and Munroe, J.: Geochemical characterization of discrete grain size fractions within contemporary alpine dust, Uinta Mountains, Utah, USA, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11041, https://doi.org/10.5194/egusphere-egu2020-11041, 2020.

Atmospheric aerosols over polar regions have attracted considerable attention for their pivotal effects on climate change. In this study, temporospatial variations in single-particle-based depolarization ratios (δ: s-polarized component divided by the total backward scattering intensity) were studied over the Northwest Pacific and the Arctic Ocean using an optical particle counter with a depolarization module. The δ value of aerosols was 0.06 ± 0.01 for the entire observation period, 61 ± 10% lower than the observations for coastal Japan (0.12 ± 0.02) (Pan et al. Atmos. Chem. Phys. 2016, 16, 9863−9873) and inland China (0.19 ± 0.02) (Tian et al. Atmos. Chem. Phys. 2018, 18, 18203−18217) in summer. The volume concentration showed two dominant size modes at 0.9 and 2 μm. The super-micrometer particles were mostly related to sea-salt aerosols with a δ value of 0.09 over marine polar areas, ∼22% larger than in the low-latitude region because of differences in chemical composition and dry air conditions. The δ values for fine particles (<1 μm) were 0.05 ± 0.1, 50% lower than inland anthropogenic pollutants, mainly because of the complex mixtures of sub-micrometer sea salts. High particle concentrations in the Arctic Ocean could mostly be attributed to the strong marine emission of sea salt associated with deep oceanic cyclones, whereas long-range transport pollutants from the continent were among the primary causes of high particle concentrations in the Northwest Pacific region.

How to cite: Pan, X., Tian, Y., Yan, J., Lin, Q., Sun, Y., Fu, P., and Wang, Z.: Size Distribution and Depolarization Properties of Aerosol Particles over the Northwest Pacific and Arctic Ocean from Shipborne Measurements during an R/V Xuelong Cruise, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13205, https://doi.org/10.5194/egusphere-egu2020-13205, 2020.

Volcanic dust (v-dust) is a highly variable source of natural particles in the atmosphere, and during the period of high volcanic activity it can provide a large surface for heterogeneous interactions with other atmospheric compounds. With an area of 103,000 km², Iceland is the biggest volcanic desert on earth. It was chosen as a case study due to frequency of volcanic eruptions and high aeolian activity in the area. This is a comprehensive study of the heterogeneous reactivity of Icelandic volcanic dust with sulfur dioxide (SO₂) gas. First, we focused on the kinetics of the reaction of SO₂ with natural v-dust samples under atmospheric conditions using coated wall flow tube reactor. Steady-state uptake coefficients were measured to represent the long-term phenomena of the processing of aerosols in the atmosphere and the values obtained can be directly incorporated in chemical transport modeling. Second, the mechanism of the reaction of SO₂ with natural v-dust samples was studied using infrared Fourier transform spectroscopy (DRIFTS). Both sulfites and sulfates were observed on the surface of v-dust, with sulfates being the final oxidation product, attesting to SO₂ heterogeneous reactivity. Surface hydroxyl groups were found to play a crucial role in the conversion of SO₂ to sulfates as evidenced from both flow tube and DRIFTS experiments. Based on these experimental results, a mechanism for SO₂ interaction with different surface sites of v-dust was proposed and discussed. Third, in order to monitor the amount of sulfites and sulfates formed on the surface of mineral dusts of different origins a simple, accurate and precise reversed-phase liquid chromatography method was developed and validated to stabilize and analyze sulfites and sulfates in the extract of dusts exposed to SO₂. Besides SO₂ gas, v-dust reacts with other atmospheric pollutants, such as NO₂ and O₃, proving that heterogeneous processes play an important role in the atmospheric chemistry. One must keep in mind that as a result of such transformations, such properties as ice nucleation and optical properties might change as well soliciting further investigation of heterogeneous reactivity of Icelandic v-dusts.

How to cite: Urupina, D., Romanias, M., Thevenet, F., and Lasne, J.: Uptake and surface chemistry of SO2 on natural Icelandic volcanic dusts under simulated atmospheric conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-530, https://doi.org/10.5194/egusphere-egu2020-530, 2020.

Samples from the Horqin sandy land were exposed to a series of wind velocities and the sink particles were collected at the end of the diffusion section of a wind tunnel. The resulting grain size was coarser than the original one, and the original samples showed lower average content of the SiO₂ and higher average content of Al₂O₃, Fe₂O₃, MgO, CaO, Na₂O, and K₂O than the collected samples did. Comparing with other dust source area in China, the Horqin sandy land had higher content of the Zr, Ba, SiO₂, Al₂O₃ and K₂O. Compared with the average upper continental crust (UCC) composition, surface samples were rich in the content of the Y, Zr, Nb, Ba, La, Nd. Geochemistry characteristics of the fine grain components of the Horqin sandy land differ from those from other dust source regions, because the fine-grained particles in the Horqin sandy land were mostly derived from various local deposits formed in its unique depositional environments controlled by several tectonic activities.

How to cite: Zhang, C. and Wang, X.: A wind-tunnel study on the sorting effects of wind erosion towards the geochemistry and the particle size of the surface samples from the Horqin sandy land, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3894, https://doi.org/10.5194/egusphere-egu2020-3894, 2020.