Seasonal cycle of desert aerosols in western Africa: analysis of the coastal transition with passive and active sensors

Senghor, Habib; Machu, Éric; Hourdin, F.; Gaye, Amadou Thierno

doi:10.5194/acp-17-8395-2017

Cited by 26 publications

(45 citation statements)

References 111 publications

(144 reference statements)

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“…Across the entire study region, the greatest frequency of high DAOD occurs over West Africa during boreal summer, consistent with Ginoux et al (2012) based on MODIS DAOD, in apparent contradiction with the region's relatively low frequency of dust activation at that time of year. Indeed, during boreal summer, elevated West African dust aerosols (Senghor et al, 2017) are frequently transported westward ( Figure S4) over the tropical Atlantic Ocean, exerting influence on tropical cloud systems, precipitation, and hurricane development (Dunion & Velden, 2004;Evan et al, 2006;Kaufman et al, 2005;Kishcha et al, 2015). Indeed, during boreal summer, elevated West African dust aerosols (Senghor et al, 2017) are frequently transported westward ( Figure S4) over the tropical Atlantic Ocean, exerting influence on tropical cloud systems, precipitation, and hurricane development (Dunion & Velden, 2004;Evan et al, 2006;Kaufman et al, 2005;Kishcha et al, 2015).…”

Section: Seasonal Distribution Of Dust Emission and Concentrationmentioning

confidence: 99%

“…One likely cause of the widespread high DAOD over West Africa is the seasonally enhanced ascending motion during May to September ( Figure S3), which extends the lifetime of dust aerosols in the atmosphere and enables longer transport (Engelstaedter & Washington, 2007), thereby leading to broader regions of high DAOD over West Africa. Indeed, during boreal summer, elevated West African dust aerosols (Senghor et al, 2017) are frequently transported westward ( Figure S4) over the tropical Atlantic Ocean, exerting influence on tropical cloud systems, precipitation, and hurricane development (Dunion & Velden, 2004;Evan et al, 2006;Kaufman et al, 2005;Kishcha et al, 2015).…”

Section: Seasonal Distribution Of Dust Emission and Concentrationmentioning

confidence: 99%

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Identification and Characterization of Dust Source Regions Across North Africa and the Middle East Using MISR Satellite Observations

Калашникова

Garay

et al. 2018

Geophysical Research Letters

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Motivated by limitations in current satellite‐based dust source identification techniques, this study examines dust emissions and concentrations over North Africa and the Middle East during 2000–2016 by analyzing stereo and optical products from the Multiangle Imaging SpectroRadiometer instrument on the National Aeronautics and Space Administration polar‐orbiting Terra satellite. Based on the occurrence of fast‐moving, near‐surface dust plumes from the Multiangle Imaging SpectroRadiometer cloud motion vector product, dust sources in the study region are identified in geographical depressions, including the Bodélé Depression, which represents the leading source. The West African El Djouf desert generates substantial dust emissions, which are typically underestimated by aerosol loading‐based dust source identifications. In response to local vegetation cover anomalies, dust emissions and concentrations increased at 15% year−1 over the Middle East and decreased at 12% year−1over the central Sahel during 2001–2013 but partly recovered toward their climatological means afterward.

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Section: Seasonal Distribution Of Dust Emission and Concentrationmentioning

confidence: 99%

Section: Seasonal Distribution Of Dust Emission and Concentrationmentioning

confidence: 99%

Identification and Characterization of Dust Source Regions Across North Africa and the Middle East Using MISR Satellite Observations

Калашникова

Garay

et al. 2018

Geophysical Research Letters

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“…The vertical distribution of atmospheric particles between two aerosol types in the troposphere was already observed by Heese et al [17]. Despite the important quantity of the black (Figure 1(a)) and the bottom (Figure 1(b) [37]. In the following sections, we will consider that attenuated backscatter signal from aerosol was dominated by mineral dust over Dakar.…”

Section: Methodsmentioning

confidence: 54%

Seasonal Behavior of Aerosol Vertical Concentration in Dakar and Role Played by the Sea-Breeze

Senghor¹,

Machu²,

Durán³

et al. 2020

OJAP

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The Westward transport of mineral dust from the North Africa continent to Atlantic Ocean can produce poor air quality, low visibilities, and negatively impacting respiratory and cardiac health due to the optical and physical properties of aerosols. The dynamical impact of the sea-breeze on the dust vertical distribution in West Africa remains unknown. To investigate this issue, we have used in-situ measurements from lidar. We have focused on the attenuated backscatter of aerosols to study the effect of the local circulation on the vertical profile of mineral dust at land-sea transition. The results highlight a strong diurnal cycle of mineral dust associated with the nocturnal low-level jet (NLLJ). The jet is located between 500 m and 1000 m and crucially affected by the dynamic of the sea-breeze circulation.

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“…Such perturbations to the radiative budget are significant, and to the authors' knowledge it is the first time that such large values have been measured over ocean, in combination with dust in situ, vertically resolved properties. Slingo et al (2006) documented a major dust storm over Niger, with extremely high AOD peaking 3-4 and a subsequent midday solar direct radiative effect of −100 W m −2 at the TOA and −250 W m −2 at the surface. Their surface and TOA flux changes were of a similar magnitude to those measured over the dust front discussed here; however, the change per AOD unit that we observed is larger, and this can be explained with the low ocean albedo.…”

Section: Discussionmentioning

confidence: 99%

Unexpected vertical structure of the Saharan Air Layer and giant dust particles during AER-D

Marenco

Ryder

Estellés³

et al. 2018

Atmos. Chem. Phys.

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Abstract. The Saharan Air Layer (SAL) in the summertime eastern Atlantic is typically well mixed and 3–4 km deep, overlying the marine boundary layer (MBL). In this paper, we show experimental evidence that at times a very different structure can be observed. During the AERosol properties – Dust (AER-D) airborne campaign in August 2015, the typical structure described above was observed most of the time, and was associated with a moderate dust content yielding an aerosol optical depth (AOD) of 0.3–0.4 at 355 nm. In an intense event, however, an unprecedented vertical structure was observed close to the eastern boundary of the basin, displaying an uneven vertical distribution and a very large AOD (1.5–2), with most of the dust in a much lower level than usual (0.3–2 km). Estimated dust concentrations and column loadings for all flights during the campaign spanned 300–5500 and 0.8–7.5 g m−2, respectively. The shortwave direct radiative impact of the intense dust event has been evaluated to be as large as -260±30 and -120±15 W m−2 at the surface and top of atmosphere (TOA), respectively. We also report the correlation of this event with anomalous lightning activity in the Canary Islands. In all cases, our measurements detected a broad distribution of aerosol sizes, ranging from ∼0.1 to ∼80 µm (diameter), thus highlighting the presence of giant particles. Giant dust particles were also found in the MBL. We note that most aerosol models may miss the giant particles due to the fact that they use size bins up to 10–25 µm. The unusual vertical structure and the giant particles may have implications for dust transport over the Atlantic during intense events and may affect the estimate of dust deposited to the ocean. We believe that future campaigns could focus more on events with high aerosol load and that instrumentation capable of detecting giant particles will be key to dust observations in this part of the world.

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Seasonal cycle of desert aerosols in western Africa: analysis of the coastal transition with passive and active sensors

Abstract: Abstract. The impact of desert aerosols on climate, atmospheric processes, and the environment is still debated in the scientific community.

Cited by 26 publications

References 111 publications

Identification and Characterization of Dust Source Regions Across North Africa and the Middle East Using MISR Satellite Observations

Identification and Characterization of Dust Source Regions Across North Africa and the Middle East Using MISR Satellite Observations

Seasonal Behavior of Aerosol Vertical Concentration in Dakar and Role Played by the Sea-Breeze

Unexpected vertical structure of the Saharan Air Layer and giant dust particles during AER-D

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