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) “Deep Blue” 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

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

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

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 Earth’s 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 Aïr Massif in Niger with a north–south extent of 16 ∘ –22 ∘ N and an east–west extent of 4 ∘ –12 ∘ 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

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

Investigation of atmospheric conditions fostering the spreading of legionnaires’ disease in outbreaks related to cooling towers

Legionnaires’ 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 2000–2016, 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)

Quantifying Fire‐Driven Dust Emissions Using a Global Aerosol Model

Vegetation fires have become increasingly recognized as a potential entrainment mechanism for mineral dust. However, the global importance of this emission pathway remains largely unknown. Based on previous LES investigations, we developed a parameterization that relates the dust emission potential of wildfires to observational data of the fire radiative power and further soil‐surface conditions. It was implemented into the aerosol‐climate model ICON‐HAM and simulations with and without the new emission pathway were conducted for the 10‐year period 2004–2013. Fire‐dust emissions can account for around 230 (190–255) Tg yr −1 , which represents around 18 (15–21) % of the total global dust emissions. These additional emissions originate largely from regions that are typically not known as significant sources of mineral dust. Locally, wildfires can enhance the presence of atmospheric dust particles and on the Southern hemisphere might even surpass other forms of dust emission. Highly dust active fire regions are identified in areas where burning grasslands create suitable emission conditions together with emissive soil types despite rather weak fires, for example, in Eastern Europe or the Central US. Fire‐dust emissions are subject to a strong seasonal cycle, mainly driven by the fire activity, following the hemispheric warm and dry seasons. Multi‐year comparisons with (dust) AOD observations revealed improvements due to the additional fire‐dust emissions, particularly in the most fire‐active regions on the Southern hemisphere. Nevertheless, further research and improvements of the parameterization are required to better classify the source areas and their variation with the changing climate and land use conditions

Natürliche Variabilität der Wolken im Klimamodell

Wolken spielen im globalen Wasser- und Energiekreislauf eine bedeutende Rolle. Ständig sind rund 66% der Erde von Wolken bedeckt. Der Bedeckungsgrad variiert auf saisonalen, interannualen und interdekadischen Zeitskalen. In dieser Diplomarbeit soll neben der saisonalen Variabilität der Bedeckung auch die interannuale und interdekadische Variabilität des Bedeckungsgrades in einem gekoppelten Atmosphäre/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) durchgeführt. Die globale Verteilung der Gesamtbedeckung im Modell folgt entsprechend den Beobachtungsdaten der für 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 unterschätzt, in den subpolaren und polaren Breiten wird diese vom Modell überschätzt. Die saisonale Variabilität des Bedeckungsgrades wird vom Modell verstärkt 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 über gemeinsame Variabilitäten 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) überein. Im dritten Teil (Kapitel 8) dieser Arbeit wird die Variabilität der Wolkenbedeckung auf verschiedenen vertikalen Leveln im Zusammenhang mit der Variabilität der Oberflächentemperatur 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 Variabilität des Gesamtbedeckungsgrades aus Variabilitäten in unterschiedlichen Höhen und somit unterschiedlichen Wolkentypen zusammensetzt. Im letzten Teil (Kapitel 9 und 10) werden Rückkopplungen zwischen dominanten Mustern regionaler Klimavariabilität, ENSO und NAO, in Hinblick auf die Variabilität 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 beschäftigt sich mit der Charakterisierung des atmosphärischen Kreislaufs von nordafrikanischen Wüstenstaub. Dazu wurde Satellitendaten auf einer zeitlichen Auflösung von 15 Minuten hinsichtlich der Aktivierung von Staubquellen nördlich von 5°N über Afrika ausgewertet. Der Auswertezeitraum beginnt im März 2006. Der erstellte Datensatz wurde hinsichtlich der raum-zeitlichen Verteilung aktiver Staubquellen untersucht. Die räumlich Verteilung der Staubquellen zeigt die Bedeutung von Trockentälern im Zuge der Staubmobilisierung auf. Die zeitliche Verteilung einsetzender Staubmobilisierung zeigt ein Maximum während der lokalen Morgenstunden. Mit Hilfe von regionaler Modellierung wurden diese Ereignisse im Zusammenhang mit dem Heruntermischen des nächtlichen Grenzschichtstrahlstroms untersucht. Im Weiteren wurde der saisonale Staubexport Richtung tropischen Atlantik mit untersucht