Modelling an exceptional desert dust transport toward Portugal on February 2017

2020 ◽  
Author(s):  
Maria João Costa ◽  
Flavio Couto ◽  
Eduardo Cardoso ◽  
Rui Salgado ◽  
Juan Luis Guerrero-Rascado
Keyword(s):  
Iberian Peninsula ◽  
Atmospheric Circulation ◽  
Dust Emission ◽  
Horizontal Resolution ◽  
Sahara Desert ◽  
Dust Transport ◽  
Western Sahara ◽  
Orographic Effects ◽  
Desert Dust ◽  
The North

<p>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.</p>

scholarly journals North African dust transport toward the western Mediterranean basin: Atmospheric controls on dust source activation and transport pathways during June–July 2013

2016 ◽  
Author(s):  
Kerstin Schepanski ◽  
Marc Mallet ◽  
Bernd Heinold ◽  
Max Ulrich
Keyword(s):  
Atmospheric Circulation ◽  
Mediterranean Basin ◽  
Dust Emission ◽  
Western Mediterranean ◽  
North African ◽  
Atmospheric Dust ◽  
Dust Source ◽  
Dust Transport ◽  
The Mediterranean ◽  
Heat Low

Abstract. Dust transported from North African source region toward the Mediterranean basin and Europe is an ubiquitous phenomenon in the Mediterranean region. Winds formed by large-scale pressure gradients foster dust entrainment into the atmosphere over North African dust source regions and advection of dust downwind. The constellation of centers of high and low pressure determines wind speed and direction, and thus the chance for dust emission over Northern Africa and transport toward the Mediterranean. Here, we present characteristics of the atmospheric dust life-cycle determining dust transport toward the Mediterranean basin. Using the atmosphere-dust model COSMO-MUSCAT (COSMO: COnsortium for Small-scale MOdelling; MUSCAT: MUltiScale Chemistry Aerosol Transport Model), a complementary analysis of dust source activation, emission fluxes, transport pathways, and deposition rates is provided with focus on the ChArMEx (Chemistry-Aerosol Mediterranean Experiment) special observation period in June and July 2013. Modes of atmospheric circulation, identified from empirical orthogonal function (EOF) analysis of the geopotential height at 850 hPa are used for investigating the characteristics of the atmospheric dust life-cycle regarding the atmospheric circulation over the Mediterranean. Two different phases are identified from the first EOF, which in total are explaining 45 % of the variance. They are characterized by the propagation of the subtropical ridge into the Mediterranean basin, the position of the Saharan heat low and the predominance Iberian heat low and discussed illustrating a dipole pattern for enhanced (reduced) dust emission fluxes, stronger (weaker) meridional dust transport, and consequent increased (decreased) atmospheric dust concentrations and deposition fluxes. In case of a predominant high pressure zone over the western and central Mediterranean (positive phase), a hot spot in dust emission flux is evident over the Grand Erg Occidental and reduced level of atmospheric dust loading occurs over the western Mediterranean basin. The meridional transport in northward direction is reduced due to prevailing northerly winds. In case of a predominant heat low trough linking the Iberian and the Sahara heat low (negative phase), meridional dust transport toward the western Mediterranean is increased due to prevailing southerly winds resulting into an enhanced atmospheric dust loading over the western Mediterranean. Altogether, results form this study illustrate the relevance of knowing dust source location in concert with atmospheric circulation. The study elaborates the question on the variability of dust transport toward the Mediterranean and Europe in dependence on the atmospheric circulation as a driver for dust emission and a determinant for dust transport routes, exemplarily for the two-month period June to July 2013. Ultimately, outcomes from this study contribute to the understanding of the variance in dust transport into a populated region.

scholarly journals An Evaluation of the CHIMERE Chemistry Transport Model to Simulate Dust Outbreaks across the North Hemisphere in March 2014

2017 ◽  
Author(s):  
Bertrand Bessagnet ◽  
Laurent Menut ◽  
Augustin Colette ◽  
Florian Couvidat ◽  
Mo Dan ◽  
...  
Keyword(s):  
Long Range ◽  
Transport Model ◽  
Global Analysis ◽  
Qualitative Evaluation ◽  
Horizontal Resolution ◽  
Dust Storms ◽  
Orographic Effects ◽  
The North ◽  
Caribbean Area ◽  
Local Budget

Mineral dust is one of the most important aerosol in mass over the world, affecting health and dynamics. This aerosol is mainly emitted over arid areas but may be long-range transported, impacting the local budget of air quality in many cities. While models were extensively used to study a single specific event, or making a global analysis at coarse resolution, the goal of our study is to simultaneously focus on several areas - Europe, North America, Central Asia, East China and the Caribbean area - for a one month period, March 2014, avoiding any parameter fitting to better simulate a given dust outbreak. The simulation is performed for the first time with the hemispheric version of the CHIMERE model, with a horizontal resolution of 10km. In this study, an overview of several simultaneous dust outbreaks over the north hemisphere is proposed to assess the capability of such modelling tools to predict dust pollution events. A quantitative and qualitative evaluation of the most striking episodes is presented with comparisons to satellite data, ground based Particulate Matter and calcium measurements. Despite some overestimation of dust concentrations far from emission areas, the model is able to simulate the timing of the arrival of dust outbreaks on observational sites. For instance, several spectacular dust storms in the US and China are perfectly captured by the models. The high resolution allows to better describe and understand the orographic effects and the long-range transport of dust plumes.

scholarly journals Airborne dust distributions over the Tibetan Plateau and surrounding areas derived from the first year of CALIPSO lidar observations

2008 ◽  
Vol 8 (16) ◽  
pp. 5045-5060 ◽  
Author(s):  
Z. Liu ◽  
D. Liu ◽  
J. Huang ◽  
M. Vaughan ◽  
I. Uno ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Time History ◽  
Dust Particles ◽  
The Tibetan Plateau ◽  
Airborne Dust ◽  
Dust Transport ◽  
Desert Dust ◽  
The North ◽  
Surrounding Areas ◽  
Lidar Observations

Abstract. Using an analysis of the first full year of CALIPSO lidar measurements, this paper derives unprecedented, altitude-resolved seasonal distributions of desert dust transported over the Tibetan Plateau (TP) and the surrounding areas. The CALIPSO lidar observations include numerous large dust plumes over the northern slope and eastern part of the TP, with the largest number of dust events occurring in the spring of 2007, and some layers being lofted to altitudes of 11–12 km. Generation of the Tibetan airborne dusts appears to be largely associated with source regions to the north and on the eastern part of the plateau. Examination of the CALIPSO time history reveals an "airborne dust corridor" due to the eastward transport of dusts originating primarily in these source areas. This corridor extends from west to east and shows a seasonality largely modulated by the TP through its dynamical and thermal forcing on the atmospheric flows. On the southern side, desert dust particles originate predominately in Northwest India and Pakistan. The dust transport occurs primarily in dry seasons around the TP western and southern slopes and dust particles become mixed with local polluted aerosols. No significant amount of dust appears to be transported over the Himalayas. Extensive forward trajectory simulations are also conducted to confirm the dust transport pattern from the nearby sources observed by the CALIPSO lidar. Comparisons with the OMI and MODIS measurements show the unique capability of the CALIPSO lidar to provide unambiguous, altitude-resolved dust measurements.

scholarly journals Diagnosis of the Relationship between Dust Storms over the Sahara Desert and Dust Deposit or Coloured Rain in the South Balkans

2010 ◽  
Vol 2010 ◽  
pp. 1-14 ◽  
Author(s):  
N. G. Prezerakos ◽  
A. G. Paliatsos ◽  
K. V. Koukouletsos
Keyword(s):  
Atmospheric Circulation ◽  
Dust Cloud ◽  
Dust Storms ◽  
Dust Particles ◽  
Sahara Desert ◽  
Synoptic Scale ◽  
Yellow Colour ◽  
Western Sahara ◽  
Sand Storm ◽  
Dust Deposits

The main objects of study in this paper are the synoptic scale atmospheric circulation systems associated with the rather frequent phenomenon of coloured rain and the very rare phenomenon of dust or sand deposits from a Saharan sandstorm triggered by a developing strong depression. Analysis of two such cases revealed that two days before the occurrence of the coloured rain or the dust deposits over Greece a sand storm appeared over the north-western Sahara desert. The flow in the entire troposphere is southerly/south-westerly with an upward vertical motion regime. If the atmospheric conditions over Greece favour rain then this rain contains a part of the dust cloud while the rest is drawn away downstream adopting a light yellow colour. In cases where the atmospheric circulation on the route of the dust cloud trajectories is not intensively anticyclonic dust deposits can occur on the surface long far from the region of the dust origin. Such was the case on 4th April, 1988, when significant synoptic-scale subsidence occurred over Italy and towards Greece. The upper air data, in the form of synoptic maps, illustrate in detail the synoptic-scale atmospheric circulations associated with the emission-transport-deposition and confirm the transportation of dust particles.

scholarly journals Seasonal changes of Sahara desert dust transport over Balkans

2021 ◽  
Vol 33 ◽  
pp. 76-86
Author(s):  
Maria Dimitrova
Keyword(s):  
Sahara Desert ◽  
Satellite Measurements ◽  
Seasonal Behavior ◽  
Dust Transport ◽  
The Balkans ◽  
Desert Dust ◽  
Space Instruments ◽  
Area Of Interest ◽  
Aerosol Index ◽  
Different Sources

This article presents an investigation of seasonal behavior of Sahara desert dust transport over the Balkans. The data used is satellite measurements of monthly averaged Absorption Aerosol Index (AAI) value. The researched period is from June 1995 till the end of 2019. The data used is from four different space instruments onboard five satellites. The area of interest is a rectangle with corners 23 E 43 N and 24 E 35 N. The data from different sources is compared and discussed.

scholarly journals Quantification of the dust optical depth across spatiotemporal scales with the MIDAS global dataset (2003–2017)

2021 ◽  
Author(s):  
Antonis Gkikas ◽  
Emmanouil Proestakis ◽  
Vassilis Amiridis ◽  
Stelios Kazadzis ◽  
Enza Di Tomaso ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Optical Depth ◽  
Northern Hemisphere ◽  
Boreal Summer ◽  
Transport Pathways ◽  
Lake Chad ◽  
Dust Transport ◽  
Western Sahara ◽  
The North ◽  
Spatiotemporal Scales

Abstract. Quantifying the dust optical depth (DOD) and its uncertainty across spatiotemporal scales is key to understanding and constraining the dust cycle and its interactions with the Earth System. This study quantifies the DOD along with its monthly and year-to-year variability between 2003 and 2017 at global and regional levels based on the MIDAS (ModIs Dust AeroSol) dataset, which combines MODIS-Aqua retrievals and MERRA-2 reanalysis products. We also describe the annual and seasonal geographical distributions of DOD across the main dust source regions and transport pathways. MIDAS provides columnar mid-visible (550 nm) DOD at fine spatial resolution (0.1° × 0.1°), expanding the current observational capabilities for monitoring the highly variable spatiotemporal features of the dust burden. We obtain a global DOD of 0.032 ± 0.003 – approximately a quarter (23.4 % ± 2.4 %) of the global AOD – with about one order of magnitude more DOD in the northern hemisphere (0.056 ± 0.004; 31.8 % ± 2.7 %) than in the southern hemisphere (0.008 ± 0.001; 8.2 % ± 1.1 %) and about 3.5 times more DOD over land (0.070 ± 0.005) than over ocean (0.019 ± 0.002). The northern hemisphere monthly DOD is highly correlated with the corresponding monthly AOD (R2 = 0.94) and contributes 20 % to 48 % of it, both indicating a dominant dust contribution. In contrast, the contribution of dust to the monthly AOD does not exceed 17 % in the southern hemisphere, although the uncertainty in this region is larger. Among the major dust sources of the planet, the maximum DODs (~1.2) are recorded in the Bodélé Depression of the northern Lake Chad Basin, whereas moderate-to-high intensities are encountered in the Western Sahara (boreal summer), along the eastern parts of the Middle East (boreal summer) and in the Taklamakan Desert (spring). Over oceans, major long-range dust transport is observed primarily along the Tropical Atlantic (intensified during boreal summer) and secondarily in the North Pacific (intensified during boreal spring). Our calculated global and regional averages and associated uncertainties are consistent with some but not all recent observationally based studies. Our work provides a simple, yet flexible method to estimate consistent uncertainties across spatiotemporal scales, which will enhance the use of the MIDAS dataset in future studies.

The conflict in Western Sahara – an unresolved issue from the decolonization period

2002 ◽  
Vol 5 ◽  
pp. 375-380 ◽  
Author(s):  
Hans-Peter Gasser
Keyword(s):  
Atlantic Coast ◽  
Small Towns ◽  
Sahara Desert ◽  
Unresolved Issue ◽  
African Continent ◽  
Western Sahara ◽  
North West ◽  
The North ◽  
North Western ◽  
Phosphate Deposits

The territory of Western Sahara has an area of about 280,000 sq. km and approximately 250,000 inhabitants, known as Sahrawis. It is situated in the north-west of the African continent, where the Sahara Desert meets the Atlantic Ocean, and has a coastline of more than 1,000 km. In the north, Western Sahara has a common border of 443 km with Morocco, and in the south and west it is bordered by Mauritania (1,561 km). The territory also has a short common border of 42 km with Algeria. The climate is predominantly that of the desert: hot and dry in summer, cold in winter, with little or no rainfall. In the coastal regions vegetation may be abundant. While the Sahrawis were originally nomads, most of the population now lives in small towns and villages. The economy is based on agriculture and fishing, primarily destined for local consumption. Rich phosphate deposits are the main export commodity. There seem to be oil deposits off the Atlantic coast.

scholarly journals Rapid increase in simulated North Atlantic dust deposition due to fast change of northwest African landscape during the Holocene

2018 ◽  
Author(s):  
Sabine Egerer ◽  
Martin Claussen ◽  
Christian Reick
Keyword(s):  
North Atlantic ◽  
Marine Sediment ◽  
Dust Emission ◽  
Sudden Increase ◽  
Dust Deposition ◽  
North African ◽  
Western Sahara ◽  
The North ◽  
Dust Sources ◽  
Sediment Records

Abstract. Marine sediment records from a series of core sites along the northwest African margin show a sudden increase in North Atlantic dust deposition about 5 ka BP that has been associated with an abrupt end of the African Humid Period (AHP). To assess the causes of the abrupt shift in North Atlantic dust deposition, we explore changes in the Holocene dust cycle and in North African climate and landscape by performing several time slice simulations from 8 ka BP until the pre-industrial era. Therefore, we use the coupled aerosol-climate model ECHAM6-HAM2 including dynamic vegetation and interactive dust, whereas ocean conditions and lake surface area are prescribed for each time slice. We find a rapid increase in simulated dust deposition between 6 and 4 ka BP that is fairly consistent with the abrupt change in marine sediment records at around 20° N. The rapid change in simulated dust deposition is caused by a rapid increase in simulated dust emission in the western Sahara, where the main dust sources for dust transport towards the North Atlantic are located. The sudden increase in dust emission in the western Sahara is according to our simulations a consequence of a fast decline of vegetation cover from 22° N to 18° N that might occur due to vegetation-climate feedbacks or due to the existence of a precipitation threshold on vegetation growth. Additionally, the prescribed gradual reduction of lake area enforces accelerated dust release as highly productive dust sources are uncovered. Changes in the Saharan landscape and dust emission south of 18° N and in the eastern Sahara as well as changes in atmospheric circulation play a minor role in driving the dynamics of North Atlantic dust deposition at the core sites. Our study identifies spatial and temporal heterogeneity in the transition of the North African landscape. As a consequence, implications from local data records on large scale climate have to be treated with caution.

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