Harmattan, Saharan heat low, and West African monsoon circulation: modulations on the Saharan dust outflow towards the North Atlantic
The outflow of dust from the northern African continent towards the North Atlantic is stimulated by the atmospheric circulation over North Africa, which modulates the spatio-temporal distribution of dust source activation and consequently the entrainment of mineral dust into the boundary layer,...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2017-09-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/17/10223/2017/acp-17-10223-2017.pdf |
| _version_ | 1819171566278148096 |
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| author | K. Schepanski B. Heinold I. Tegen |
| author_facet | K. Schepanski B. Heinold I. Tegen |
| author_sort | K. Schepanski |
| collection | DOAJ |
| description | The outflow of dust from the northern African continent towards the
North Atlantic is stimulated by the atmospheric circulation over North
Africa, which modulates the spatio-temporal distribution of dust source
activation and consequently the entrainment of mineral dust into the boundary
layer, as well as the transport of dust out of the source regions. The
atmospheric circulation over the North African dust source regions,
predominantly the Sahara and the Sahel, is characterized by three major
circulation regimes: (1) the harmattan (trade winds), (2) the Saharan heat
low (SHL), and (3) the West African monsoon circulation. The strength of the
individual regimes controls the Saharan dust outflow by affecting the
spatio-temporal distribution of dust emission, transport pathways, and
deposition fluxes.<br><br>This study aims at investigating the atmospheric
circulation pattern over North Africa with regard to its role favouring dust
emission and dust export towards the tropical North Atlantic. The focus of
the study is on summer 2013 (June to August), during which the SALTRACE
(Saharan Aerosol Long-range TRansport and Aerosol-Cloud interaction
Experiment) field campaign also took place. It involves satellite observations by
the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) flying on board
the geostationary Meteosat Second Generation (MSG) satellite, which are
analysed and used to infer a data set of active dust sources. The
spatio-temporal distribution of dust source activation frequencies (DSAFs)
allows for linking the diurnal cycle of dust source activations to dominant
meteorological controls on dust emission. In summer, Saharan dust source
activations clearly differ from dust source activations over the Sahel
regarding the time of day when dust emission begins. The Sahara is dominated
by morning dust source activations predominantly driven by the breakdown of
the nocturnal low-level jet. In contrast, dust source activations in the
Sahel are predominantly activated during the second half of the day, when
downdrafts associated with deep moist convection are the major atmospheric
driver. Complementary to the satellite-based analysis on dust source
activations and implications from their diurnal cycle, simulations on
atmosphere and dust life cycle were performed using the mesoscale
atmosphere–dust model system COSMO-MUSCAT (COSMO: COnsortium for Small-scale
MOdelling; MUSCAT: MUltiScale Chemistry Aerosol Transport Model). Fields from
this simulation were analysed regarding the variability of the harmattan, the
Saharan heat low, and the monsoon circulation as well as their impact on the
variability of the Saharan dust outflow towards the North Atlantic. This
study illustrates the complexity of the interaction among the three major
circulation regimes and their modulation of the North African dust outflow.
Enhanced westward dust fluxes frequently appear following a phase
characterized by a deep SHL. Ultimately, findings from this study contribute
to the quantification of the interannual variability of the atmospheric dust
burden. |
| first_indexed | 2024-12-22T19:53:19Z |
| format | Article |
| id | doaj.art-3f7dd1127a2e48dc8e933af5e609c643 |
| institution | Directory Open Access Journal |
| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-12-22T19:53:19Z |
| publishDate | 2017-09-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-3f7dd1127a2e48dc8e933af5e609c6432022-12-21T18:14:29ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242017-09-0117102231024310.5194/acp-17-10223-2017Harmattan, Saharan heat low, and West African monsoon circulation: modulations on the Saharan dust outflow towards the North AtlanticK. Schepanski0B. Heinold1I. Tegen2Leibniz Institute for Tropospheric Research (TROPOS), Leipzig, GermanyLeibniz Institute for Tropospheric Research (TROPOS), Leipzig, GermanyLeibniz Institute for Tropospheric Research (TROPOS), Leipzig, GermanyThe outflow of dust from the northern African continent towards the North Atlantic is stimulated by the atmospheric circulation over North Africa, which modulates the spatio-temporal distribution of dust source activation and consequently the entrainment of mineral dust into the boundary layer, as well as the transport of dust out of the source regions. The atmospheric circulation over the North African dust source regions, predominantly the Sahara and the Sahel, is characterized by three major circulation regimes: (1) the harmattan (trade winds), (2) the Saharan heat low (SHL), and (3) the West African monsoon circulation. The strength of the individual regimes controls the Saharan dust outflow by affecting the spatio-temporal distribution of dust emission, transport pathways, and deposition fluxes.<br><br>This study aims at investigating the atmospheric circulation pattern over North Africa with regard to its role favouring dust emission and dust export towards the tropical North Atlantic. The focus of the study is on summer 2013 (June to August), during which the SALTRACE (Saharan Aerosol Long-range TRansport and Aerosol-Cloud interaction Experiment) field campaign also took place. It involves satellite observations by the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) flying on board the geostationary Meteosat Second Generation (MSG) satellite, which are analysed and used to infer a data set of active dust sources. The spatio-temporal distribution of dust source activation frequencies (DSAFs) allows for linking the diurnal cycle of dust source activations to dominant meteorological controls on dust emission. In summer, Saharan dust source activations clearly differ from dust source activations over the Sahel regarding the time of day when dust emission begins. The Sahara is dominated by morning dust source activations predominantly driven by the breakdown of the nocturnal low-level jet. In contrast, dust source activations in the Sahel are predominantly activated during the second half of the day, when downdrafts associated with deep moist convection are the major atmospheric driver. Complementary to the satellite-based analysis on dust source activations and implications from their diurnal cycle, simulations on atmosphere and dust life cycle were performed using the mesoscale atmosphere–dust model system COSMO-MUSCAT (COSMO: COnsortium for Small-scale MOdelling; MUSCAT: MUltiScale Chemistry Aerosol Transport Model). Fields from this simulation were analysed regarding the variability of the harmattan, the Saharan heat low, and the monsoon circulation as well as their impact on the variability of the Saharan dust outflow towards the North Atlantic. This study illustrates the complexity of the interaction among the three major circulation regimes and their modulation of the North African dust outflow. Enhanced westward dust fluxes frequently appear following a phase characterized by a deep SHL. Ultimately, findings from this study contribute to the quantification of the interannual variability of the atmospheric dust burden.https://www.atmos-chem-phys.net/17/10223/2017/acp-17-10223-2017.pdf |
| spellingShingle | K. Schepanski B. Heinold I. Tegen Harmattan, Saharan heat low, and West African monsoon circulation: modulations on the Saharan dust outflow towards the North Atlantic Atmospheric Chemistry and Physics |
| title | Harmattan, Saharan heat low, and West African monsoon circulation: modulations on the Saharan dust outflow towards the North Atlantic |
| title_full | Harmattan, Saharan heat low, and West African monsoon circulation: modulations on the Saharan dust outflow towards the North Atlantic |
| title_fullStr | Harmattan, Saharan heat low, and West African monsoon circulation: modulations on the Saharan dust outflow towards the North Atlantic |
| title_full_unstemmed | Harmattan, Saharan heat low, and West African monsoon circulation: modulations on the Saharan dust outflow towards the North Atlantic |
| title_short | Harmattan, Saharan heat low, and West African monsoon circulation: modulations on the Saharan dust outflow towards the North Atlantic |
| title_sort | harmattan saharan heat low and west african monsoon circulation modulations on the saharan dust outflow towards the north atlantic |
| url | https://www.atmos-chem-phys.net/17/10223/2017/acp-17-10223-2017.pdf |
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