106 research outputs found
Characterising Saharan Dust Sources and Export using Remote Sensing and Regional Modelling
The PhD-thesis aims to characterise the Saharan dust cycle at diffent seasons using satellite remote sensing techniques and regional modelling studies. A dust index based on 15-minute infrared satellite measurements provided by the SEVIRI instrument onboard the Meteosat Second Generation (MSG) satellite is used to infer spatio-temporal charcteristics of dust sources north of 5°N over Africa since March 2006. The spatial distribution of dust sources points towards the importance of endorehic drainage systems in mountain areas. The temporal distribution of the time-of-day when dust mobilisation starts shows maximum activity during local morning hours, pointing towards the role of the breakdown of the nocturnal low-level jet. Details of the role and ability of the low-level jet breakdown for dust entrainment were studied using regional modelling. Furthermore, the seasonal dust export towards the tropical North Atlantic is considered using regional modelling
Saharan dust transport and deposition towards the tropical northern Atlantic
We present a study of Saharan dust export towards the tropical North Atlantic using the regional dust emission, transport and deposition model LM-MUSCAT. Horizontal and vertical distribution of dust optical thickness, concentration, and dry and wet deposition rates are used to describe seasonality of dust export and deposition towards the eastern Atlantic for three typical months in different seasons. Deposition rates strongly depend on the vertical dust distribution, which differs with seasons. Furthermore the contribution of dust originating from the Bodélé Depression to Saharan dust over the Atlantic is investigated. A maximum contribution of Bodélé dust transported towards the Cape Verde Islands is evident in winter when the Bodélé source area is most active and dominant with regard to activation frequency and dust emission. Limitations of using satellite retrievals to estimate dust deposition are highlighted
Where dirty air is most dangerous
Exposure to poor air quality can damage human health and incur associated costs. The severity of these impacts is not uniform around the globe, but depends on the health and density of the populations
Recommended from our members
Identification of dust sources in a Saharan dust hot-spot and their implementation in a dust-emission model
Although mineral dust plays a key role in the Earthâs climate system and in climate and weather prediction, models still have difficulties in predicting the amount and distribution of mineral dust in the atmosphere. One reason for this is the limited understanding of the distribution of dust sources and their behavior with respect to their spatiotemporal variability in activity. For a better estimation of the atmospheric dust load, this paper presents an approach to localize dust sources and thereby estimate the sediment supply for a study area centered on the AĂŻr Massif in Niger with a northâsouth extent of 16 â â22 â N and an eastâwest extent of 4 â â12 â E. This approach uses optical Sentinel-2 data at visible and near infrared wavelengths together with HydroSHEDS flow accumulation data to localize ephemeral riverbeds. Visible channels from Sentinel-2 data are used to detect sand sheets and dunes. The identified sediment supply map was compared to the dust source activation frequency derived from the analysis of Desert-Dust-RGB imagery from the Meteosat Second Generation series of satellites. This comparison reveals the strong connection between dust activity, prevailing meteorology and sediment supply. In a second step, the sediment supply information was implemented in a dust-emission model. The simulated emission flux shows how much the model results benefit from the updated sediment supply information in localizing the main dust sources and in retrieving the seasonality of dust activity from these sources. The described approach to characterize dust sources can be implemented in other regional model studies, or even globally, and can thereby help to get a more accurate picture of dust source distribution and a more realistic estimation of the atmospheric dust load
Recommended from our members
Investigation of atmospheric conditions fostering the spreading of legionnairesâ disease in outbreaks related to cooling towers
Legionnairesâ disease (LD) is a severe lung infection caused by the bacteria Legionella pneumophila which is usually associated with water managing installations like cooling towers. Several outbreaks of LD have been linked to individual sources of bioaerosol in the past. However, the transmission pathways as well as the influence of meteorological factors in the spreading of such bioaerosols remain unclear. Using the meteorological data near 12 LD outbreaks in Europe for the period 2000â2016, the correlation between key meteorological factors and the occurrence of LD was assessed. Temperature, humidity, atmospheric pressure, wind speed, precipitation, cloud cover and, for the first time, fog occurrence were included as potential risk factors. It was found that the occurrence of fog was related to four of the LD outbreaks, suggesting that the presence of fog droplets and/or the thermal inversions associated with fog may play a role in the disease spreading. This finding can contribute to outbreak investigations and to the prevention of future outbreaks. © 2019, The Author(s)
Recommended from our members
Climate Feedback on Aerosol Emission and Atmospheric Concentrations
Purpose of Review: Climate factors may considerably impact on natural aerosol emissions and atmospheric distributions. The interdependencies of processes within the aerosol-climate system may thus cause climate feedbacks that need to be understood. Recent findings on various major climate impacts on aerosol distributions are summarized in this review. Recent Findings: While generally atmospheric aerosol distributions are influenced by changes in precipitation, atmospheric mixing, and ventilation due to circulation changes, emissions from natural aerosol sources strongly depend on climate factors like wind speed, temperature, and vegetation. Aerosol sources affected by climate are desert sources of mineral dust, marine aerosol sources, and vegetation sources of biomass burning aerosol and biogenic volatile organic gases that are precursors for secondary aerosol formation. Different climate impacts on aerosol distributions may offset each other. Summary: In regions where anthropogenic aerosol loads decrease, the impacts of climate on natural aerosol variabilities will increase. Detailed knowledge of processes controlling aerosol concentrations is required for credible future projections of aerosol distributions
Remote sensing of mineral dust over land with MSG infrared channels: A new Bitemporal Mineral Dust Index
A new Bitemporal Mineral Dust Index (BMDI) is derived from Meteosat Second Generation (MSG) infrared observations over land at two different time slots per day.
This daily dust index is evaluated with AErosol RObotic NETwork (AERONET) surface observations, MODerate resolution Imaging Spectro-radiometer (MODIS) âDeep Blueâ Aerosol Optical Depth (AOD) and Ozone Monitoring Instrument (OMI) Aerosol Index, showing a good capability of the BMDI for dust detection and dust load estimation over land and also over deserts. BMDI dust detection is shown to be limited in scenes with high atmospheric humidity as e.g. coastal regions. In particular the insensitivity of BMDI to biomass burning aerosol is shown, leading to the possibility of remote sensing of mineral dust also in regions with large contributions of biomass burning aerosol to the total column aerosol concentrations. Time series of mineral dust as inferred from BMDI for the year 2006 are presented for four regions over the Sahara. These time series show strong (and different) annual cycles of dust load for all four regions. Especially the strong episodic character of atmospheric dust in the main source regions can be inferred from BMDI observations
NatĂŒrliche VariabilitĂ€t der Wolken im Klimamodell
Wolken spielen im globalen Wasser- und Energiekreislauf eine bedeutende Rolle. StÀndig sind rund 66% der Erde von Wolken bedeckt. Der Bedeckungsgrad variiert auf saisonalen, interannualen und interdekadischen Zeitskalen.
In dieser Diplomarbeit soll neben der saisonalen VariabilitÀt der Bedeckung auch die interannuale und interdekadische VariabilitÀt des Bedeckungsgrades in einem gekoppelten AtmosphÀre/Ozean Zirkulationsmodell ECHAM5/NEMO untersucht werden. Im weiteren werden Wechselwirkungen zwischen dem Bedeckungsgrad und anderen Klimavariablen (SST, Bodenluftdruck, Niederschlag) betrachtet.
Im ersten Teil (Kapitel 5 und 6) der vorliegenden Arbeit wird zur Validierung der Modelldaten eine Vergleichsstudie mit globaler Wolkenbedeckung aus Satellitenbeobachtungen des International Satellite Cloud Climatology Project (ISCCP) durchgefĂŒhrt. Die globale Verteilung der Gesamtbedeckung im Modell folgt entsprechend den Beobachtungsdaten der fĂŒr die verschiedenen Klimazonen typischen Verteilung. Es zeigen sich jedoch lokale Differenzen. So ist die globale Gesamtbedeckung im Model global um 2,46% höher als beobachtet. Die Gesamtbedeckung in den Tropen, Subtropen und Teilen der mittleren Breiten wird vom Modell unterschĂ€tzt, in den subpolaren und polaren Breiten wird diese vom Modell ĂŒberschĂ€tzt. Die saisonale VariabilitĂ€t des Bedeckungsgrades wird vom Modell verstĂ€rkt wiedergegeben. Diese Unterschiede wurden auch in anderen Vergleichsstudien zwischen modellierter Bedeckung in GCMs und Satellitendaten gefunden.
Der zweite Teil (Kapitel 7) dieser Diplomarbeit beschreibt Korrelationsanalysen zwischen dem Bedeckungsgrad und der SST sowie dem Bodenluftdruck. Anhand dieser Korrelationsanalysen werden Aussagen ĂŒber gemeinsame VariabilitĂ€ten getroffen. Ziel ist es, Wechselwirkungen aufzuzeigen. Im Vergleich zwischen modellierter und beobachteter SST zeigen sich Abweichungen von bis zu 6 K. Ein Vergleich von Korrelationen zwischen Bedeckungsgrad und SST sowohl mit Modelldaten als auch mit Beobachtungsdaten zeigt jedoch, dass die Haupkorrelationsmuster vom Modell wiedergegeben werden. Jedoch können aufgrund der gröberen Auflösung im Modell kleinskalige Wechselwirkungen nicht im Detail wiedergegeben werden.
Neben der SST nimmt der Bodenluftdruck starken Einfluss auf die Wolkenbedeckung. Muster hoher Korrelationen stimmen jedoch nur bedingt mit der klimatologischen Verteilung des Bodenluftdrucks und seinen Drucksystemen (Hochdruckgebiete, Tiefdruckgebiete) ĂŒberein.
Im dritten Teil (Kapitel 8) dieser Arbeit wird die VariabilitÀt der Wolkenbedeckung auf verschiedenen vertikalen Leveln im Zusammenhang mit der VariabilitÀt der OberflÀchentemperatur und dem Bodenlufdruck untersucht. So kann gezeigt werden, dass Rahmenbedingungen am Boden wie Luftdruck und Temperatur mit Wolken in unterschiedlichen Höhen unterschiedlich stark wechselwirken. Im weiteren wird deutlich, dass sich der Anteil der VariabilitÀt des Gesamtbedeckungsgrades aus VariabilitÀten in unterschiedlichen Höhen und somit unterschiedlichen Wolkentypen zusammensetzt.
Im letzten Teil (Kapitel 9 und 10) werden RĂŒckkopplungen zwischen dominanten Mustern regionaler KlimavariabilitĂ€t, ENSO und NAO, in Hinblick auf die VariabilitĂ€t des Bedeckungsgrades untersucht
Charakterisierung von Quellen und Transport von Saharastaub durch Fernerkundung und regionale Modellierung
The PhD-thesis aims to characterise the Saharan dust cycle at diffent seasons using satellite remote sensing techniques and regional modelling studies. A dust index based on 15-minute infrared satellite measurements provided by the SEVIRI instrument onboard the Meteosat Second Generation (MSG) satellite is used to infer spatio-temporal charcteristics of dust sources north of 5°N over Africa since March 2006. The spatial distribution of dust sources points towards the importance of endorehic drainage systems in mountain areas. The temporal distribution of the time-of-day when dust mobilisation starts shows maximum activity during local morning hours, pointing towards the role of the breakdown of the nocturnal low-level jet. Details of the role and ability of the low-level jet breakdown for dust entrainment were studied using regional modelling. Furthermore, the seasonal dust export towards the tropical North Atlantic is considered using regional modelling.Die Arbeit beschĂ€ftigt sich mit der Charakterisierung des atmosphĂ€rischen Kreislaufs von nordafrikanischen WĂŒstenstaub. Dazu wurde Satellitendaten auf einer zeitlichen Auflösung von 15 Minuten hinsichtlich der Aktivierung von Staubquellen nördlich von 5°N ĂŒber Afrika ausgewertet. Der Auswertezeitraum beginnt im MĂ€rz 2006. Der erstellte Datensatz wurde hinsichtlich der raum-zeitlichen Verteilung aktiver Staubquellen untersucht. Die rĂ€umlich Verteilung der Staubquellen zeigt die Bedeutung von TrockentĂ€lern im Zuge der Staubmobilisierung auf. Die zeitliche Verteilung einsetzender Staubmobilisierung zeigt ein Maximum wĂ€hrend der lokalen Morgenstunden. Mit Hilfe von regionaler Modellierung wurden diese Ereignisse im Zusammenhang mit dem Heruntermischen des nĂ€chtlichen Grenzschichtstrahlstroms untersucht. Im Weiteren wurde der saisonale Staubexport Richtung tropischen Atlantik mit untersucht
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, 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.
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 atmosphereâdust 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
- âŠ