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Land–atmosphere interactions govern the process of dust emission and transport. An accurate depiction of these physical processes within numerical weather prediction models allows for better estimating the spatial and temporal distribution of the dust burden and the characterisation of source and recipient areas. In the presented study, the ECMWF-IFS (European Centre for Medium-Range Weather Forecast – Integrated Forecasting System) outputs, produced with and without the assimilation of Aeolus quality-assured Rayleigh–clear and Mie–cloudy horizontal line-of-sight wind profiles, are used as initial or boundary conditions in the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) to simulate 2-month periods in the spring and autumn of 2020, focusing on a case study in October. The experiments have been performed over the broader eastern Mediterranean and Middle East (EMME) region, which is frequently subjected to dust transport, as it encompasses some of the most active erodible dust sources. Aerosol- and dust-related model outputs (extinction coefficient, optical depth and concentrations) are qualitatively and quantitatively evaluated against ground- and satellite-based observations. Ground-based columnar and vertically resolved aerosol optical properties are acquired through AERONET sun photometers and PollyXT lidar, while near-surface concentrations are taken from EMEP. Satellite-derived vertical dust and columnar aerosol optical properties are acquired through LIVAS (LIdar climatology of Vertical Aerosol Structure) and MIDAS (ModIs Dust AeroSol), respectively. Overall, in cases of either high or low aerosol loadings, the model predictive skill is improved when WRF-Chem simulations are initialised with the meteorological fields of Aeolus wind profiles assimilated by the IFS. The improvement varies in space and time, with the most significant impact observed during the autumn months in the study region. Comparison with observation datasets saw a remarkable improvement in columnar aerosol optical depths, vertically resolved dust mass concentrations and near-surface particulate concentrations in the assimilated run against the control run. Reductions in model biases, either positive or negative, and an increase in the correlation between simulated and observed values was achieved for October 2020.

One of the deficiencies of atmospheric dust models is that they struggle to accurately reproduce the transport of coarse and giant dust particles, according to observational evidence. Among the reasons behind that model incapacity that have been proposed in the literature, is the issue of numerical diffusion inside the advection codes of the models. In this study, we examine the importance of that issue in the WRF-L model. To do so, we update the default numerical scheme (UPWIND) which is used for the vertical advection of dust due to gravitational settling. The diffusive UPWIND scheme is replaced with a non-diffusive one, named UNO3 (third-order Upstream Non-Oscillatory scheme). To test the code performance, we perform simulations reproducing the 2D transport of a dust plume which is released at 4 km height above Cabo Verde towards Barbados. The model is initialized on 13/06/2014 at 12 UTC (which coincides with the day of the SALTRACE flight above Cabo Verde) using meteorological conditions of radiosonde from Tenerife airport and wind profile based on ECMWF model climatology. The results suggest that, in the UNO3 simulation, dust particles with a diameter 26 μm can be transported more than 500 km longer than in the BASE simulation and the dust in the atmosphere can be 10% more in the UNO3 simulation compared to the BASE simulation. In future studies, the UNO3 scheme will be tested in other aerosol types also (e.g. volcanic ash, smoke from fires).Acknowledgements: Authors acknowledge support by the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the “2nd Call for H.F.R.I. Research Projects to support Post-Doctoral Researchers” (Project Acronym: StratoFIRE, Project number: 3995) and the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (Project Acronym: D-TECT, Grant Agreement: 725698).

Aeolus, ESA’s space mission, provides vertical profiles of the HLOS wind component in the troposphere and the lower stratosphere. In addition, ALADIN thanks to its HSLR configuration retrieves and provides profiles of extinction/backscatter coefficients of aerosols and clouds (known as spin-off or L2A products), at the ultraviolet region of the spectrum (355nm). However, ALADIN’s design enables the detection only of the returned co-polar component of the transmitted light. This inherent limitation hampers the ability of ALADIN to provide realistic optical products (i.e., underestimated backscatter coefficient profiles) when non-spherical particles (e.g., dust, volcanic ash, cirrus ice crystals) are probed, a deficiency for the case of Earth Observation of highly depolarizing targets with negative impacts on applications of Data Assimilation (DA) and Numerical Weather Prediction (NWP). The ESA L2A+ (Enhancing Aeolus L2A for depolarizing targets and impact on aerosol research and NWP) project kicked off in November 2022, with an overarching objective to develop a refined Aeolus L2A aerosol product (L2A+) and test its application for enhancing aerosol research. The generation of the refined L2A+ Aeolus aerosol optical product will be based, among others, on an integrated approach of novel algorithms (i.e., AEL-FM/AEL-PRO), model outputs (i.e., CAMS), advanced EO-based products (i.e., MSG, MODIS-MIDAS), existing climatologies (ESA-LIVAS), and AOD retrievals from Aeolus itself. The product will be thoroughly compared with L2A and validated against quality-assured measurements from the ESA-ASKOS/JATAC experiment in Cape Verde. With respect to the overarching objectives on aerosol research, L2A+ aims to (1) examine the impact of L2A and L2A+ on aerosol assimilation and dust transport models, (2) assess the impact of Aeolus on NWP, (3) highlight the benefit of the Aeolus joint aerosol and wind assimilation for simulating dust deposition fields, (4) assess the climatological value of L2A+ for aerosol databases such as the ESA-LIVAS long-term climate dataset, and (5) assess the impact of the novel L2A+ product on aerosol assimilation, towards improved dust transport modelling and for further enhancing NWP. The ESA-L2A+ project focuses on the broader the Western Sahara and the Tropical Atlantic Ocean, while due to the extensive wealth of available observational data collected in the framework of the European Space Agency (ESA) ASKOS Tropical Campaign in Cape Verde, which are needed for a complete and descriptive assessment analysis of the project outputs and the evaluation of the enhanced L2A+ product, the developments and experiments will be performed for September 2021. Preliminary results from the project will be presented. The L2A+ team acknowledges support by ESA in the framework of the "Enhancing Aeolus L2A for depolarizing targets and impact on aerosol research and NWP project (4000139424/22/I-NS).

Land–atmosphere interactions govern the process of dust emission and transport. An accurate depiction of these physical processes within numerical weather prediction models allows for better estimating the spatial and temporal distribution of the dust burden and the characterisation of source and recipient areas. In the presented study, the ECMWF-IFS (European Centre for Medium-Range Weather Forecast – Integrated Forecasting System) outputs, produced with and without the assimilation of Aeolus quality-assured Rayleigh–clear and Mie–cloudy horizontal line-of-sight wind profiles, are used as initial or boundary conditions in the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) to simulate 2-month periods in the spring and autumn of 2020, focusing on a case study in October. The experiments have been performed over the broader eastern Mediterranean and Middle East (EMME) region, which is frequently subjected to dust transport, as it encompasses some of the most active erodible dust sources. Aerosol- and dust-related model outputs (extinction coefficient, optical depth and concentrations) are qualitatively and quantitatively evaluated against ground- and satellite-based observations. Ground-based columnar and vertically resolved aerosol optical properties are acquired through AERONET sun photometers and PollyXT lidar, while near-surface concentrations are taken from EMEP. Satellite-derived vertical dust and columnar aerosol optical properties are acquired through LIVAS (LIdar climatology of Vertical Aerosol Structure) and MIDAS (ModIs Dust AeroSol), respectively. Overall, in cases of either high or low aerosol loadings, the model predictive skill is improved when WRF-Chem simulations are initialised with the meteorological fields of Aeolus wind profiles assimilated by the IFS. The improvement varies in space and time, with the most significant impact observed during the autumn months in the study region. Comparison with observation datasets saw a remarkable improvement in columnar aerosol optical depths, vertically resolved dust mass concentrations and near-surface particulate concentrations in the assimilated run against the control run. Reductions in model biases, either positive or negative, and an increase in the correlation between simulated and observed values was achieved for October 2020.

Dust particles larger than 20 µm in diameter (0.2 μm < D < 100 µm) have been regularly observed to remain airborne during long-range transport. In this work we extend the parameterization of mineral dust cycle in the GOCART-AFWA dust scheme of WRFV4.2.1, to include also such coarse and giant particles. The initial particle size distribution in our parameterization is based on observations over desert dust sources and the Stokes’ drag coefficient has also been updated to account for dust particles of all sizes (Re < 105). The new code is applied to simulate dust transport over Cape Verde during the August 2015 AER -D campaign. Model results are evaluated using both airborne dust measurements and the CALIPSO-LIVAS pure dust product. The results show that the modeled lifetimes of the coarser particles are shorter than those observed. Various processes are proposed to explain such inaccuracies, such as the electric field inside dust plumes and non-spherical aerodynamics. Additional sensitivity runs are performed by artificially reducing the settling velocities of the particles to compensate for such underrepresented processes in the model. Our simulations show that particles with diameters of 5–17 μm and 40–100 μm are better represented assuming 80 % reduction in settling velocity (UR80) while particles at the range 17–40 μm are better represented in the UR60 scenario. The overall statistical analysis shows that the UR80 experiment presents the closest agreement with the airborne in situ measurements both in Cape Verde and over the sources. The UR80 experiment improves also the vertical distribution of dust in the model, as compared to the CALIPSO-LIVAS pure dust product. Further research is requested in order to understand the physical processes behind the reduction of settling velocity.

Throughout the year, the Tropical Atlantic Ocean receives constantly enormous amounts of mineral particles emitted over the western Sahara. Despite the numerous efforts, the current state-of-the-art atmospheric-dust models are not yet able to represent adequately the Saharan dust outflows towards the Atlantic Ocean. Several drawbacks in the relevant parameterization schemes can explain this deficiency, which subsequently hampers an optimal assessment of the dust-induced impacts. One of these aspects is the wind acting as the driving force of dust emission and transport. Thanks to the deployment of the ALADIN (Atmospheric Laser Doppler Lidar) lidar, onboard the European Space Agency (ESA) Aeolus satellite, profiles of HLOS (Horizontal Line-Of-Sight) winds are acquired globally up to a maximum of 30 km altitude. This unique global dataset is filling an existing observational gap in the Tropics, among other regions of the planet. In addition, the assimilation of Aeolus HLOS winds has revealed an improvement in numerical weather predictions (NWP), particularly in the Tropics where the major portion of the global dust budget resides.The improvements of NWP are expected to also advance dust numerical simulations. Such hypothesis is under investigation in the NEWTON (ImproviNg dust monitoring and forEcasting through Aeolus Wind daTa assimilatiON) project funded by ESA under the Aeolus+Innovation framework. To address the NEWTON scientific objective, short-term regional dust forecasts, relying on the WRF model operating at the National Observatory of Athens (NOA), are conducted. More specifically, two WRF runs are performed using boundary and initial conditions from the ECMWF IFS (Integrated Forecasting System) outputs, produced with (hel4) and without (hel1) the assimilation of Aeolus quality screened Rayleigh-clear and Mie-cloudy wind profiles. Our simulation domain encompasses most part of the Sahara Desert and the Atlantic Ocean, bounded between the Equator and mid-latitudes. Focus is given on September 2021, when the JATAC (Joint Aeolus Tropical Atlantic Campaign) campaign took place in Cape Verde providing reference observations (ground-based, airborne) valuable for a comprehensive evaluation of WRF dust-related outputs. The assessment analysis is further extended by utilizing the satellite dust datasets MIDAS (ModIs Dust AeroSol) and LIVAS (LIdar climatology of Vertical Aerosol Structure for space-based lidar simulation studies), both developed at NOA, providing columnar dust optical depth and vertical profiles of dust extinction, respectively. Finally, all the NEWTON related activities are disseminated via the official website (https://newton.space.noa.gr) and the EO4Society portal (https://eo4society.esa.int/).

The long–range transport of larger than expected dust particles has been established in numerous observational studies. However, dust transport models struggle to simulate the observed particle size distributions. Studies utilizing a new version of WRF-chem code that contains the full size range of dust particles (0.2-100μm in diameter), estimated that approximately 80% reduction in the particles’ settling velocity is required for the particles to be transported from the desert towards the Cape Verde. Here, we examine the effect of the dust particles’ shape in the dynamics of coarse and giant long-range transport. We specifically apply a new drag coefficient for spheroids in idealized atmospheric WRF-chem simulations above the Atlantic Ocean. Additionally, since there is much confusion about the definition of the size of non-spherical dust particles, where some studies define size as the diameter of a sphere with the same volume, while others as the particles’ maximum, we perform simulations comparing the spherical and spheroid dust particles using both those two different approaches. The results are encouraging for the explanation of long –range dust transport, however more processes should be re-visited, including the dust radiation effects of non-spherical articles.AcknowledgementsThis research was supported by D-TECT (Grant Agreement 725698) funded by the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme. Eleni Drakaki is funded by Stavros Niarchos Foundation (SNF) Fellowship.

Σκοπός της εργασίας υπήρξε η διερεύνηση και ερμηνεία της σχέσης ανάμεσα στο μετασχηματισμό της ελληνικής οικονομίας και στην άνιση περιφερειακή ανάπτυξη για μία συγκεκριμένη ιστορική περίοδο που ξεκινά το 1993 και φτάνει μέχρι το 2010. Η χωρική – οικονομική αναδιάρθρωση στην Ελλάδα εξετάστηκε υπό το θεωρητικό πρίσμα της πολιτικής οικονομίας και της κριτικής Γεωγραφίας, μέσα από τρείς αναλυτικούς άξονες, όπως το κράτος, οι περιφέρειες και η παραγωγή. Η κεντρική παραδοχή υπήρξε ότι η άνιση ανάπτυξη βρίσκεται σε άμεση συνάρτηση με τις ευρύτερες πολιτικοοικονομικές διαδικασίες, μέσα από τις οποίες διαμορφώνεται και τις οποίες διαμορφώνει. Η ανασύνθεση, συγκέντρωση και μελέτη διάσπαρτου υλικού που συμπεριλάμβανε στατιστικά στοιχεία, δημοσιεύματα, νομικά κείμενα και κείμενα πολιτικής και επιστημονική βιβλιογραφία, είχε ως απώτερο στόχο την περιγραφή, κατανόηση και ερμηνεία του περιφερειακού προβλήματος και του τρόπου με τον οποίο η κεντρική εξουσία εργάστηκε σε ότι αφορά τη διαχείριση του. Αυτό που προκύπτει είναι κυρίως ότι το ζήτημα της περιφερειακής ανάπτυξης στις διάφορες μορφές που μπορεί να λάβει στις χωρικές κλίμακες και μέσα από εναλλακτικές προσεγγίσεις, συνεισέφερε στην Ελλάδα του εκσυγχρονισμού και της ευρωπαϊκής ολοκλήρωσης, στην εκτόνωση εντάσεων και αντιφάσεων που ενείχε ο ριζικός μετασχηματισμός της οικονομίας, οι οποίες αν δεν αναχαιτίζονταν θα έφερναν ενδεχομένως το σύστημα νωρίτερα στην κρίση. Τελικά τέθηκε ειδικά για την ελληνική περίπτωση, το κλασικό ερώτημα που διατύπωσε η D. Massey τη δεκαετία 1970 «με ποια έννοια περιφερειακό πρόβλημα» και σε αυτό δόθηκαν απαντήσεις. Η εργασία υποστηρίζει ότι το περιφερειακό πρόβλημα είναι πρόβλημα όχι των λιγότερο ανεπτυγμένων περιφερειών ή περιοχών, αλλά της οικονομίας και της πολιτικής. Επίσης, είναι πρόβλημα της μίας δυναμικής περιφέρειας της μεγέθυνσης που παρασύρει ολόκληρο το σύστημα στη σύγκλιση, αλλά ταυτόχρονα, υπονομεύει τις προϋποθέσεις της ύπαρξης και της υπεροχής της, αποδιοργανώνοντας την παραγωγική δυναμικότητα της ευρύτερης επικράτειας της. Η θέση αυτή, βασισμένη στην υπόθεση ότι ο χώρος του «περιφερειακού» πλάθεται, συντίθεται και αποσυντίθεται, μέσα στο χρόνο και σε εναλλακτικές χωρικότητες, διαφοροποιείται τελικά από τις συνήθεις απόψεις για την περιφερειακή ανάπτυξη στην Ελλάδα. Καταρχήν, αμφισβητεί την παραδοχή ότι η γρήγορη ανάπτυξη της περιόδου υπήρξε μία μονοσήμαντα θετική εξέλιξη, απλά γιατί είχε οφέλη στο εισόδημα και στην απασχόληση και σε ορισμένα βασικά μακροοικονομικά μεγέθη, ακόμα και σε κοινωνικές παροχές και πρόσθετους πόρους στις περιφέρειες. Η ανάπτυξη παρήγαγε νέους διαχωρισμούς, ανισότητες και αποκλεισμούς στο χώρο σε επιμέρους πεδία και τομείς. Παράλληλα εφιστά την προσοχή στους μηχανισμούς της κεντρικής παρέμβασης και τους κοινωνικούς αυτοματισμούς που οδήγησαν σε αφομοίωση των ευρωπαϊκών κατευθύνσεων σε μία άκριτη δέσμευση σε μέσα και κατευθύνσεις, εκτός ενός συνεκτικού και μακροπρόθεσμου στρατηγικού πλαισίου. Σε γενικές γραμμές, υποστηρίζεται ότι η ανάπτυξη στις περιφέρειες χρησιμοποιήθηκε για να εξυπηρετηθεί η εθνική σύγκλιση στο πλαίσιο της οικονομικής ολοκλήρωσης, αλλά και για την εξασφάλιση μίας θεμελιώδους κοινωνικής συναίνεσης σε υψηλής διακινδύνευσης κυβερνητικές επιλογές και αποφάσεις.

The effects of non sphericity and particle orientation on mineral dust gravitational settling are studied for prolate spheroids in the range of Reynolds number up to 100. New drag coefficients for prolate spheroids are defined that take into account the orientation of the particle. The drag coefficients along with the slip correction factors are applied to the momentum equation, which is numerically solved for the calculation of the steady state velocity of the particle with respect to the air. As the aspect ratio increases, the settling velocity of ellipsoids decreases compared to the settling velocity of spherical particles, and the non spherical particles can remain in the atmosphere for longer periods. Moreover, the settling velocity of horizontally oriented particles is smaller than the settling velocity of vertically oriented particles. Assuming that at time t = 0 s the particles are at altitude equal to 6 km, non spherical particles that are horizontally oriented, with aspect ratio equal to 2.4, and polar diameter up to ∼ 24 μ m can remain in the atmosphere for 5 days, while particles with polar diameter up to ∼ 17 μ m can remain in the atmosphere for 10 days. In the case that the particles are vertically oriented, particles with polar diameter up to ∼ 22 μ m can remain in the atmosphere for 5 days, and particles with polar diameter up to ∼ 15 μ m can remain in the atmosphere for 10 days.

Dust particles larger than 20 µm in diameter have been regularly observed to remain airborne during long-range transport. In this work, we modify the parameterization of the mineral dust cycle in the GOCART-AFWA dust scheme of WRFV4.2.1 to also include such coarse and giant particles, and we further discuss the underlying misrepresented physical mechanisms which hamper the model in reproducing adequately the transport of the coarse and giant mineral particles. The initial particle size distribution is constrained by observations over desert dust sources. Furthermore, the Stokes drag coefficient has been updated to account for realistic dust particle sizes (Re < 105). The new code was applied to simulate dust transport over Cabo Verde in August 2015 (AER-D campaign). Model results are evaluated against airborne dust measurements and the CALIPSO-LIVAS pure dust product. The results show that the modeled lifetimes of the coarser particles are shorter than those observed. Several sensitivity runs are performed by reducing artificially the particles' settling velocities in order to compensate underrepresented mechanisms, such as the non-spherical aerodynamics, in the relevant parameterization schemes. Our simulations reveal that particles with diameters of 5.5–17 and 40–100 µm are better represented under the assumption of an 80 % reduction in the settling velocity (UR80), while particles with sizes ranging between 17 and 40 µm are better represented in a 60 % reduction in settling velocity (UR60) scenario. The overall statistical analysis indicates that the best agreement with airborne in situ measurements downwind (Cabo Verde) is achieved with a 40 % reduction in settling velocity (UR40). Moreover, the UR80 experiment improves the representation of the vertical structure of the dust layers as those are captured by the CALIPSO-LIVAS vertically resolved pure dust observations. The current study highlights the necessity of upgrading the existing model parameterization schemes of the dust life-cycle components towards improving the assessment of the dust-related impacts within the Earth–atmosphere system.

Corrigendum to “Effects of dust particle sphericity and orientation on their gravitational settling in the Earth's atmosphere” [Journal of Aerosol Science 150 (2020) 105634]