scholarly journals Temporal variability of mineral dust concentrations over West Africa: analyses of a pluriannual monitoring from the AMMA Sahelian Dust Transect

2010 ◽  
Vol 10 (18) ◽  
pp. 8899-8915 ◽  
Author(s):  
B. Marticorena ◽  
B. Chatenet ◽  
J. L. Rajot ◽  
S. Traoré ◽  
M. Coulibaly ◽  
...  
Keyword(s):  
West Africa ◽  
Rainy Season ◽  
Seasonal Cycle ◽  
Mineral Dust ◽  
General Pattern ◽  
Regional Scale ◽  
Surface Wind ◽  
Dry Season ◽  
Dust Concentration ◽  
Saharan Dust

Abstract. The Sahelian belt is known to be a region where atmospheric levels of suspended mineral dust are among the highest observed on Earth. In the framework of the AMMA (African Monsoon Multidisciplinary Analysis) International Program, a transect of 3 ground based stations, the "Sahelian Dust Transect" (SDT), has been deployed in order to obtain quantitative information on the mineral dust content and its variability over the Sahel. The three stations, namely Banizoumbou (Niger), Cinzana (Mali) and M'Bour (Senegal) are aligned around 14° N along the east-westward main pathway of the Saharan and Sahelian dust towards the Atlantic Ocean. We discuss data collected between January 2006 and December 2008 to investigate the main characteristics of the mineral dust concentration over West Africa and their connection with the dominant meteorological situations. The succession of the dry season during which the Sahel is under the influence of the dry Harmattan wind and the wet season induced by the entrance of the monsoon flow is clearly identified from the basic meteorological parameters (air temperature and moisture, wind direction). Atmospheric dust concentrations at the three stations exhibit a similar seasonal cycle, with a monthly maximum during the dry season and a minimum occurring during the rainy season, indicating that the general pattern of dust concentration is similar at regional scale. This seasonal cycle of the dust concentrations is not phased with the seasonal cycle of surface wind velocity locally measured, suggesting that it is mainly controlled by Saharan dust transport. Local dust emissions induced by strong surface winds are responsible for the occurrence of extremely high daily concentrations observed at the beginning of the rainy season. A decrease in the dust concentration is observed when moving from Niger to Senegal.

scholarly journals Temporal variability of mineral dust concentrations over West Africa: analyses of a pluriannual monitoring from the AMMA Sahelian Dust Transect

2010 ◽  
Vol 10 (3) ◽  
pp. 8051-8101 ◽  
Author(s):  
B. Marticorena ◽  
B. Chatenet ◽  
J. L. Rajot ◽  
S. Traoré ◽  
M. Coulibaly ◽  
...  
Keyword(s):  
West Africa ◽  
Rainy Season ◽  
Seasonal Cycle ◽  
Mineral Dust ◽  
General Pattern ◽  
Regional Scale ◽  
Surface Wind ◽  
Dry Season ◽  
Dust Concentration ◽  
Dust Content

Abstract. The Sahelian belt is known to be a region where the mineral dust content is among the highest observed on Earth. In the framework of the AMMA (African Monsoon Multidisciplinary Analysis) International Program, a transect of 3 ground based stations, the "Sahelian Dust Transect" (SDT), has been deployed in order to obtain quantitative information on the mineral dust content and its variability over the Sahel. The three stations, namely Banizoumbou (Niger), Cinzana (Mali) and M'Bour (Senegal) are aligned around 14° N along the east-west main pathway of the Saharan and Sahelian dust towards the Atlantic Ocean. We discuss data collected between January 2006 and December 2008 to investigate the main characteristics of the mineral dust concentration over West Africa and their connection with the dominant meteorological situations. The succession of the dry season during which the Sahel is under the influence of the dry Harmattan wind and the wet season induced by the entrance of the monsoon flow is clearly identified from the basic meteorological parameters (air temperature and moisture, wind direction). Atmospheric dust concentrations at the three stations exhibit a similar seasonal cycle, with a monthly maximum during the dry season and a minimum occurring during the rainy season, indicating that the general pattern of dust concentration is similar at regional scale. This seasonal cycle of the dust concentrations is not phased with the seasonal cycle of surface wind velocity suggesting that it is mainly controlled by Saharan dust transport. A decrease in the dust concentration is observed when moving from Niger to Senegal. However, local dust emissions induced by strong surface winds are responsible for the occurrence of extremely high daily concentrations observed at the beginning of the rainy season.

scholarly journals Variability of mineral dust deposition in the western Mediterranean basin and south-east of France

2016 ◽  
Vol 16 (14) ◽  
pp. 8749-8766 ◽  
Author(s):  
Julie Vincent ◽  
Benoit Laurent ◽  
Rémi Losno ◽  
Elisabeth Bon Nguyen ◽  
Pierre Roullet ◽  
...  
Keyword(s):  
Mediterranean Basin ◽  
Mineral Dust ◽  
Sampling Site ◽  
Regional Scale ◽  
Western Mediterranean ◽  
Saharan Dust ◽  
Deposition Flux ◽  
Dust Deposition ◽  
Western Mediterranean Basin ◽  
Provenance Areas

Abstract. Previous studies have provided some insight into the Saharan dust deposition at a few specific locations from observations over long time periods or intensive field campaigns. However, no assessment of the dust deposition temporal variability in connection with its regional spatial distribution has been achieved so far from network observations over more than 1 year. To investigate dust deposition dynamics at the regional scale, five automatic deposition collectors named CARAGA (Collecteur Automatique de Retombées Atmosphériques insolubles à Grande Autonomie in French) have been deployed in the western Mediterranean region during 1 to 3 years depending on the station. The sites include, from south to north, Lampedusa, Majorca, Corsica, Frioul and Le Casset (southern French Alps). Deposition measurements are performed on a common weekly period at the five sites. The mean dust deposition fluxes are higher close to the northern African coasts and decrease following a south–north gradient, with values from 7.4 g m−2 year−1 in Lampedusa (35°31′ N, 12°37′ E) to 1 g m−2 year−1 in Le Casset (44°59′ N, 6°28′ E). The maximum deposition flux recorded is of 3.2 g m−2 wk−1 in Majorca with only two other events showing more than 1 g m−2 wk−1 in Lampedusa, and a maximum of 0.5 g m−2 wk−1 in Corsica. The maximum value of 2.1 g m−2 year−1 observed in Corsica in 2013 is much lower than existing records in the area over the 3 previous decades (11–14 g m−2 year−1). From the 537 available samples, 98 major Saharan dust deposition events have been identified in the records between 2011 and 2013. Complementary observations provided by both satellite and air mass trajectories are used to identify the dust provenance areas and the transport pathways from the Sahara to the stations for the studied period. Despite the large size of African dust plumes detected by satellites, more than 80 % of the major dust deposition events are recorded at only one station, suggesting that the dust provenance, transport and deposition processes (i.e. wet vs. dry) of dust are different and specific for the different deposition sites in the Mediterranean studied area. The results tend to indicate that wet deposition is the main form of deposition for mineral dust in the western Mediterranean basin, but the contribution of dry deposition (in the sense that no precipitation was detected at the surface) is far from being negligible, and contributes 10 to 46 % to the major dust deposition events, depending on the sampling site.

scholarly journals Radiative forcing associated with a springtime case of Bodélé and Sudan dust transport over West Africa

2010 ◽  
Vol 10 (4) ◽  
pp. 8811-8858 ◽  
Author(s):  
C. Lemaître ◽  
C. Flamant ◽  
J. Cuesta ◽  
J.-C. Raut ◽  
P. Chazette ◽  
...  
Keyword(s):  
West Africa ◽  
Heating Rate ◽  
Radiative Forcing ◽  
Mineral Dust ◽  
Regional Scale ◽  
Longwave Radiation ◽  
Heating Rates ◽  
Dust Layer ◽  
In Situ Observations

Abstract. The radiative forcing due to mineral dust over West Africa is investigated using the radiative code STREAMER, as well as remote sensing and in situ observations gathered during the African Monsoon Multidisciplinary Analysis Special Observing Period (AMMA SOP). We focus on two days (13 and 14 June 2006) of an intense and long-lasting episode of dust being lifted in remote sources in Chad and Sudan and transported across West Africa in the African easterly jet region, during which airborne operations were conducted at the regional scale, from the southern fringes of the Sahara to the Gulf of Guinea. Profiles of heating rates are computed from airborne LEANDRE 2 and space-borne CALIOP lidar observations using two mineral dust model constrained by airborne in situ data and ground-based sunphotometer obtained during the campaign. Complementary space-borne observations (from MODIS) and in-situ observations such as dropsondes are also used to take into account a realistic infrared contribution of the water vapour. We investigate the variability of the heating rate on the vertical within a dust plume, as well as the contribution of longwave radiation to the heating rate and the radiative forcing of dust during the nighttime. The sensitivity of the so-derived heating rate is also analyzed for some key variables for which the associated uncertainties are quite large. During daytime, the warming associated with the presence of dust was found to be between 1.5 K day−1 and 4 K day−1, on average, depending on altitude and latitude. Strong warming (i.e. heating rates as high as 8 K day−1) was also observed locally in some limited part of the dust plumes. Obviously, during nighttime much smaller values of heating/cooling are retrieved (less than ±1 K day−1) but large enough to modify the low tropospheric equilibrium. Furthermore, cooling is observed as the result of the longwave forcing in the dust layer, while warming is observed below the dust layer, in the monsoon layer.

scholarly journals The role of aerosol–radiation–cloud interactions in linking anthropogenic pollution over southern west Africa and dust emission over the Sahara

2019 ◽  
Vol 19 (23) ◽  
pp. 14657-14676 ◽  
Author(s):  
Laurent Menut ◽  
Paolo Tuccella ◽  
Cyrille Flamant ◽  
Adrien Deroubaix ◽  
Marco Gaetani
Keyword(s):  
West Africa ◽  
Mineral Dust ◽  
Surface Wind ◽  
Dust Emission ◽  
Longwave Radiation ◽  
Atmospheric Composition ◽  
Anthropogenic Emissions ◽  
Dust Emissions ◽  
Aerosol Cloud ◽  
The Impact

Abstract. The aerosol direct and indirect effects are studied over west Africa in the summer of 2016 using the coupled WRF-CHIMERE regional model including aerosol–cloud interaction parameterization. First, a reference simulation is performed and compared with observations acquired during the Dynamics-aerosol-chemistry-cloud interactions in West Africa (DACCIWA) field campaign which took place in June and July 2016. Sensitivity experiments are also designed to gain insights into the impact of the aerosols dominating the atmospheric composition in southern west Africa (one simulation with halved anthropogenic emissions and one with halved mineral dust emissions). The most important effect of aerosol–cloud interactions is found for the mineral dust scenario, and it is shown that halving the emissions of mineral dust decreases the 2 m temperature by 0.5 K and the boundary layer height by 25 m on a monthly average (July 2016) and over the Saharan region. The presence of dust aerosols also increases (decreases) the shortwave (longwave) radiation at the surface by 25 W m−2. It is also shown that the decrease of anthropogenic emissions along the coast has an impact on the mineral dust load over west Africa by increasing their emissions in the Saharan region. It is due to a mechanism where particulate matter concentrations are decreased along the coast, imposing a latitudinal shift of the monsoonal precipitation and, in turn, an increase of the surface wind speed over arid areas, inducing more mineral dust emissions.

Ice nucleating particle concentrations in Dust Regional Atmospheric Model (DREAM) – going one step further

2021 ◽  
Author(s):  
Luka Ilić ◽  
Eleni Marinou ◽  
Aleksandar Jovanović ◽  
Maja Kuzmanoski ◽  
Slobodan Ničković
Keyword(s):  
Field Experiments ◽  
Mineral Dust ◽  
Atmospheric Model ◽  
Dust Concentration ◽  
Saharan Dust ◽  
Dust Particles ◽  
Vertical Profiles ◽  
Regional Atmospheric Model ◽  
Immersion Freezing ◽  
The Mediterranean

<p>Mineral dust particles in the atmosphere have a large influence on the physical properties of clouds and their lifecycle. Findings from field experiments, modeling, and laboratory studies suggest that mineral dust particles are very efficient ice-nucleating particles (INPs) even in regions distant from the desert sources. The major sources of mineral dust present in the Mediterranean basin are located in the Sahara Desert. Understanding the significance of mineral dust in ice initiation led to the development of INPC parameterizations in presence of dust for immersion freezing and deposition nucleation processes. These parameterizations were mineralogically indifferent, estimating the dust ice nucleating particle concentrations (INPCs) based on dust concentration and thermodynamic parameters. In recent studies, feldspar and quartz minerals have shown to be significantly more efficient INPs than other minerals found in dust. These findings led to the development of mineralogy-sensitive immersion freezing parameterizations. In this study, we implement mineralogy-sensitive and mineralogically-indifferent INPC parameterizations into a regional coupled atmosphere-dust numerical model. We use the Dust Regional Atmospheric Model (DREAM) to perform one month of simulations of the atmospheric cycle of dust and its feldspar and quartz fractions during Saharan dust intrusion events in the Mediterranean. EARLINET (European Aerosol Lidar Network) and AERONET (AErosol RObotic NETwork) measurements are used with POLIPHON algorithm (Polarization Lidar Photometer Networking) to derive cloud-relevant dust concentration profiles. We compare DREAM results with lidar-based vertical profiles of dust mass concentration, surface area concentration, number concentration, and INPCs. This analysis is a step towards the systematic analysis of dust concentration and INPC parameterizations performance when compared to lidar derived vertical profiles.</p>

The Madden–Julian Oscillation’s Influence on Spring Rainy Season Precipitation over Equatorial West Africa*

2015 ◽  
Vol 28 (22) ◽  
pp. 8653-8672 ◽  
Author(s):  
Fisseha Berhane ◽  
Benjamin Zaitchik ◽  
Hamada S. Badr
Keyword(s):  
Indian Ocean ◽  
West Africa ◽  
Rainy Season ◽  
Regional Scale ◽  
Relative Strength ◽  
Boreal Summer ◽  
Kelvin Wave ◽  
Equatorial Wave ◽  
The Indian Ocean ◽  
Rain Rates

Abstract This paper characterizes the influence of the Madden–Julian oscillation (MJO) on spring rainy season (March–June) convection variability over equatorial West Africa (EWA) and investigates mechanisms of association. It is found that the MJO has a significant impact on convection and precipitation anomalies over the region. Over large portions of EWA, MJO impacts on rainfall constitute a difference on the order of 20%–50% from average daily rain rates for the season. This impact is primarily due to the direct influence of the eastward movement of the MJO convective core into EWA, which is associated with westerly low-level wind anomalies that advect moisture from the Atlantic Ocean to the region. In addition, equatorial Rossby and Kelvin waves triggered by MJO convection anomalies over the Indian Ocean have a significant and systematic influence on EWA spring rainy season precipitation. The Kelvin wave contribution and the relative strength of the direct MJO convective influence compared to that of equatorial wave activity differs from findings of studies that have examined MJO influence on EWA during boreal summer. In addition, MJO is found to influence precipitation extremes during spring rains in a manner that is not observed in summer. Importantly, in this analysis the influences of MJO convection and each of the MJO-associated convectively coupled equatorial waves frequently coincide, reaching EWA approximately 20 days after MJO convection initiates in the Indian Ocean. This coincident timing enhances the total MJO impact on the region, and it also implies that MJO events have potential for prediction of regional-scale convection and rainfall anomalies over EWA in this season.

scholarly journals Variability of mineral dust deposition in the western Mediterranean basin and South-East of France

2015 ◽  
Vol 15 (23) ◽  
pp. 34673-34717 ◽  
Author(s):  
J. Vincent ◽  
B. Laurent ◽  
R. Losno ◽  
E. Bon Nguyen ◽  
P. Roullet ◽  
...  
Keyword(s):  
Mediterranean Basin ◽  
Mineral Dust ◽  
Sampling Site ◽  
Regional Scale ◽  
Western Mediterranean ◽  
Saharan Dust ◽  
Deposition Flux ◽  
Dust Deposition ◽  
Western Mediterranean Basin ◽  
Provenance Areas

Abstract. Previous studies have provided some insight into the Saharan dust deposition at a few specific locations from observations over long time periods or intensive field campaigns. However, no assessment of the dust deposition temporal variability in connection with its regional spatial distribution has been achieved so far from network observations over more than one year. To investigate dust deposition dynamics at the regional scale, five automatic deposition collectors named CARAGA ("Collecteur Automatique de Retombées Atmosphériques insolubles à Grande Autonomie" in French) have been deployed in the western Mediterranean region during one to three years depending on the station. The sites include, from South to North, Lampedusa Isl., Mallorca Isl., Corsica Isl., Frioul Isl. and Le Casset (South of French Alps). Deposition measurements are performed on a common weekly period at the 5 sites. The mean Saharan dust deposition fluxes are higher close to the North African coasts and decrease following a South to North gradient, with values from 7.4 g m−2 yr−1 in Lampedusa (35°31' N–12°37' E) to 1 g m−2 yr−1 in Le Casset (44°59' N–6°28' E). The maximum deposition flux recorded is of 3.2 g m−2 wk−1 in Mallorca with only 2 other events showing more than 1 g m−2 wk−1 in Lampedusa, and a maximum of 0.5 g m−2 wk−1 in Corsica. The maximum value of 2.1 g m−2 yr−1 observed in Corsica in 2013 is much lower than existing records in the area over the 3 previous decades (11–14 g m−2 yr−1). From the 537 available samples, ninety eight major Saharan dust deposition events have been identified in the records between 2011 and 2013. Complementary observations provided by both satellite and air mass trajectories are used to identify the dust provenance areas and the transport pathways from the Sahara to the stations. Despite the large size of African dust plumes detected by satellites, more than eighty percent of the major dust deposition events are recorded at only one station, suggesting that the dust provenance, transport, and deposition processes (i.e. wet vs. dry) of dust are different and specific for the different deposition sites in the Mediterranean studied area. The results also show that wet deposition is the main way of deposition for mineral dust in the western Mediterranean basin, but the contribution of dry deposition is far to be negligible, and contributes by 15 to 46 % to the major dust deposition events, depending on the sampling site.

scholarly journals Atmospheric dust modeling from meso to global scales with the online NMMB/BSC-Dust model – Part 2: Experimental campaigns in Northern Africa

2011 ◽  
Vol 11 (11) ◽  
pp. 30273-30331 ◽  
Author(s):  
K. Haustein ◽  
C. Pérez ◽  
J. M. Baldasano ◽  
O. Jorba ◽  
S. Basart ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Initial Conditions ◽  
Regional Scale ◽  
Surface Wind ◽  
Companion Paper ◽  
Northern Africa ◽  
Saharan Dust ◽  
Temperature Cycle ◽  
Daily Maximum ◽  
Model Initialization

Abstract. The new online NMMB/BSC-Dust model is intended to provide short to medium-range weather and dust forecasts from regional to global scales. The companion paper Pérez et al., 2011 develops the dust model parameterizations and provides daily to annual evaluations of the model for its global and regional configurations. Modeled aerosol optical depth (AOD) was evaluated against AERONET Sun photometers over Northern Africa, Middle East and Europe with correlations around 0.6–0.7 on average without dust data assimilation. In this paper we analyze in detail the behavior of the model using data from the Saharan Mineral dUst experiment (SAMUM-1) in 2006 and the Bodélé Dust Experiment (BoDEx) in 2005. AOD from satellites and Sun photometers, vertically resolved extinction coefficients from lidars and particle size distributions at the ground and in the troposphere are used, complemented by wind profile data and surface meteorological measurements. All simulations were performed at the regional scale for the Northern African domain at the expected operational resolution of 25 km. Model results for SAMUM-1 generally show good agreement with satellite data over the most active Saharan dust sources. The model reproduces the AOD from Sun photometers close to sources and after long-range transport, and the dust size spectra at different height levels. At this resolution, the model is not able to reproduce a large haboob occurred during the campaign. Some deficiencies are found concerning the vertical distribution. The mixing height is underestimated which may be attributed to poor soil initial conditions. For the BoDEx period, particular attention is paid to understand the dust model behavior in relation with the low level jet (LLJ) in the Bodélé. The diurnal temperature cycle depends strongly on the soil moisture, which is underestimated in the NCEP analysis used for model initialization. The daily maximum surface wind speeds are underestimated up to 50% in some days even when using a more accurate soil moisture initialization. The dust plume over the Bodélé is well reproduced by the model and the reductions in the threshold friction velocity substantially reduce the negative AOD bias in the model due to wind speed underestimation. The LLJ is also well reproduced, which is remarkable given the rather poor model initialization with NCEP-FNL data.

scholarly journals Atmospheric dust modeling from meso to global scales with the online NMMB/BSC-Dust model – Part 2: Experimental campaigns in Northern Africa

2012 ◽  
Vol 12 (6) ◽  
pp. 2933-2958 ◽  
Author(s):  
K. Haustein ◽  
C. Pérez ◽  
J. M. Baldasano ◽  
O. Jorba ◽  
S. Basart ◽  
...  
Keyword(s):  
Regional Scale ◽  
Surface Wind ◽  
Companion Paper ◽  
Horizontal Resolution ◽  
Northern Africa ◽  
Saharan Dust ◽  
Temperature Cycle ◽  
Time Step ◽  
Wind Speeds ◽  
Dust Modeling

Abstract. The new NMMB/BSC-Dust model is intended to provide short to medium-range weather and dust forecasts from regional to global scales. It is an online model in which the dust aerosol dynamics and physics are solved at each model time step. The companion paper (Pérez et al., 2011) develops the dust model parameterizations and provides daily to annual evaluations of the model for its global and regional configurations. Modeled aerosol optical depth (AOD) was evaluated against AERONET Sun photometers over Northern Africa, Middle East and Europe with correlations around 0.6–0.7 on average without dust data assimilation. In this paper we analyze in detail the behavior of the model using data from the Saharan Mineral dUst experiment (SAMUM-1) in 2006 and the Bodélé Dust Experiment (BoDEx) in 2005. AOD from satellites and Sun photometers, vertically resolved extinction coefficients from lidars and particle size distributions at the ground and in the troposphere are used, complemented by wind profile data and surface meteorological measurements. All simulations were performed at the regional scale for the Northern African domain at the expected operational horizontal resolution of 25 km. Model results for SAMUM-1 generally show good agreement with satellite data over the most active Saharan dust sources. The model reproduces the AOD from Sun photometers close to sources and after long-range transport, and the dust size spectra at different height levels. At this resolution, the model is not able to reproduce a large haboob that occurred during the campaign. Some deficiencies are found concerning the vertical dust distribution related to the representation of the mixing height in the atmospheric part of the model. For the BoDEx episode, we found the diurnal temperature cycle to be strongly dependant on the soil moisture, which is underestimated in the NCEP analysis used for model initialization. The low level jet (LLJ) and the dust AOD over the Bodélé are well reproduced. The remaining negative AOD bias (due to underestimated surface wind speeds) can be substantially reduced by decreasing the threshold friction velocity in the model.

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