Spelling suggestions: "subject:"mineral duty.""
41 |
Characterization of mineral dust emitted from an actively retreating glacier in Yukon, CanadaBachelder, Jill 04 1900 (has links)
No description available.
|
42 |
Investigation of Mineral Dust Aerosols - Chemistry Intractions in the Marine EnvironmentsJeong, Gill-Ran 24 August 2007 (has links)
Mineral dust aerosols play an important role in atmospheric chemistry through photolysis and heterogeneous uptake. Both mechanisms strongly depend on the size and composition of mineral dust. Because of the complex nature of dust, chemistry modeling commonly relies on simplified assumptions about the properties of dust particles relevant to physiochemical processes. The goal of this thesis is to investigate the impact of size-resolved composition of dust aerosols on atmospheric photochemistry. The relative importance of dust characteristics in photolysis and heterogeneous loss and the relative roles of the two mechanisms on atmospheric photochemistry are investigated.
A new block of spectral aerosol optical properties was developed and incorporated into the tropospheric ultraviolet and visible radiation transfer code in order to calculate spectral actinic fluxes and photolysis rates, J-values. The Fuchs-Sutugin approximation was employed to compute mass transfer from gas to dust mineral species and heterogeneous loss rate, kloss,j. The J-values and kloss,j were incorporated into a one-dimensional photochemistry model to simulate the diurnal cycle of a vertical profile of photochemical species. Several cases of dust loading were considered in the clean and polluted marine environments. A size-resolved mineralogical composition was constructed by selecting a range of the mass fraction of the three main mineral species such as iron oxide-containing clay minerals, carbonate-containing species, and quartz.
This work demonstrates that differences in microphysical and chemical properties of mineral dust lead to the important changes in spectral optical properties, J-values, and kloss,j. It also shows that non-linear relationships of photochemical species with two mechanisms result in various changes in the photochemical oxidant fields and that the most important factor controlling the photochemistry field is the dust size distribution, followed by the amount of mineral species with high uptake coefficients and the amount of iron oxide-clay aggregates.
This work demonstrates that accounting for regional differences in microphysical and chemical properties of mineral dust will improve the assessment of the impact of mineral dust on tropospheric photochemistry. In addition, it suggests that the size and composition of mineral dust will lead to a deeper understanding of the impact of mineral dust on the global climate system.
|
43 |
Radiative Effect of Mixed Mineral Dust and Biomass Burning Aerosol in the Thermal InfraredKöhler, Claas H. 17 January 2014 (has links) (PDF)
This thesis treats the optical properties of mixed mineral dust and biomass burning aerosol in the thermal infrared (TIR) based on Fourier Transform infrared spectrometer (FTIR) measurements and radiative transfer simulations. The measurements were part of the Saharan Mineral Dust Experiment 2 (SAMUM-2) conducted from January to February 2008 at Praia, Cape Verde. The large amount of different instruments co-located at the main field site during the campaign resulted in a unique dataset comprising in-situ information and remote sensing data perfectly suited for column closure studies. The ultimate goal of this work is to investigate the consistency of microphysical and TIR remote sensing data. This is achieved by reproducing the measured radiances at top and bottom of the atmosphere (TOA, BOA) with a radiative transfer model, which assimilates the microphysical aerosol information gathered during SAMUM-2.
The first part of the thesis describes several experimental efforts, including a novel calibration method and a drift correction algorithm for the ground-based FTIR instrument operated within the scope of SAMUM-2 by the author. The second part introduces the concurrent radiative transfer library PIRATES, which has been developed in the framework of this thesis for the analysis of TIR aerosol optical properties. The third and final part of the treatise compares measured and simulated spectra for various typical scenarios encountered during SAMUM-2.
It is demonstrated in three case studies, that measured radiances in the TIR atmospheric window region (8-12 µm) can be reproduced at BOA and TOA by radiative transfer simulations assuming spheroidal model particles. Moreover,
spherical particles are shown to be an inadequate model for mineral dust aerosol
in this spectral region unless the aerosol optical depth is small.
|
44 |
Dust-related ice formation in the troposphere: A statistical analysis based on 11 years of lidar observations of aerosols and clouds over Leipzig / Staubbeinflusste Eisbildung in der Troposphäre: Statistische Untersuchungen von Aerosol- und Wolkenprofilen anhand von Lidarmessungen der Jahre 1997 bis 2008Seifert, Patric 28 July 2011 (has links) (PDF)
Im Rahmen der vorliegenden Arbeit wurde der Zusammenhang zwischen heterogener Eisbildung und Temperatur auf Basis eines 11-Jahres Lidardatensatzes untersucht, wobei besonders der potenzielle Einfluss von Wüstenstaubaerosol auf die heterogene Gefriertemperatur von unterkühlten Wasserwolken überprüft wurde. Der zugrundeliegende Lidardatensatz entstand im Rahmen von zwischen 1997 und 2008 am Leibniz-Institut für Troposphärenforschung (IfT) in Leipzig durchgeführten Lidarmessungen. Mehr als 2300 zeitlich und räumlich defifinierte Wolkenschichten wurden anhand des gemessenen linearen Depolarisationsverhältnisses als Flüssigwasserwolken oder als eisbeinhaltende Wolken klassifiziert. Dazu war es nötig, den störenden Einfluss von spiegelnden Reflektionen horizontal ausgerichteter Eiskristalle auf das gemessene Depolarisationsverhältnis zu charakterisieren. Die für die Auswertung benötigten Wolkenoberkantentemperaturen wurden aus Modelldaten oder, falls zeitnah verfügbar, aus Radiosondenprofifilen ermittelt.
Die statistische Auswertung des Wolkendatensatzes ergab, dass der Anteil an eisbeinhaltenden Wolken mit abnehmender Temperatur stark zunimmt. Wurde in Wolken mit Oberkantentemperaturen zwischen 0 und -5 °C in nur 1% aller Fälle Eis detektiert, enthielten zwischen -10 und -15 °C bereits 40% der in dem Temperaturbereich beobachteten Wolken Eis. Bei Wolkenoberkantentemperaturen unterhalb von -25 °C wurde in nahezu 100% aller Fälle Eis in den Wolken beobachtet. Ein ähnlicher Zusammenhang zwischen Temperatur und dem Anteil an eisbeinhaltenden Wolken wurde bereits in zahlreichen auf Flugzeugmessungen basierenden Studien gefunden.
In einem weiteren Schritt wurde der Wolkendatensatz mittels drei verschiedener Ansätze in einen staubbelasteten sowie einen staubfreien Teil getrennt. Dies geschah Anhand einer Trajektorien-Clusteranalyse sowie der Trennung bezüglich der von einem Mineralstaubvorhersagemodell berechneten Mineralstaubbelastung in Wolkenhöhe beziehungsweise in der gesamten Luftsäule über Leipzig. Die Trennung ergab, dass staubbelastete Wolken im Temperaturbereich zwischen -5 und -25 °C 10-30% mehr Eis beinhalten als staubfreie Wolken. Die Ergebnisse dieser Untersuchung legen deshalb nahe, dass Mineralstaub Eisbildung in unterkühlten Wolken maßgeblich fördert.
Der Vergleich des Leipziger Wolkendatensatzes mit einem auf den Kapverden gesammelten Datensatz tropischer Wolken zeigte, dass trotz vergleichbarem Einfluss von Mineralstaubaerosol Eisbildung in den Tropen erst bei um 10 K tieferen Temperaturen einsetzt. Als mögliche Einflussfaktoren wurden Unterschiede in der atmosphärischen Dynamik und die Wirkung effektiverer Eiskeime über Mitteleuropa diskutiert. / The formation and presence of ice crystals in clouds strongly determines meteorological processes as precipitation formation but also climatological parameters as the radiation budget of the atmosphere. The process of ice formation, however, is not straightforward because ice crystals and liquid water droplets can coexist at temperatures from -38 °C to 0 °C. In this temperature range, aerosol particles, so-called ice nuclei, must be present to trigger ice formation in a supercooled droplet.
From laboratory studies it is known that mineral dust particles are efficient ice nuclei. We present a statistical analysis of lidar-based observations of 2300 free-tropospheric clouds that was used to investigate the effect of mineral dust particles on the ice-formation temperature. The observations were performed at Leipzig, Germany (51° N, 12 °E). The time and height as well as the phase state (ice, liquid-water) of the observed clouds can easily be derived from the lidar data. The dust load in every observed cloud layer was determined by means of model data.
From the analysis it was found that dust-affected clouds produce ice 50% more frequently than dust-free clouds at temperatures between -20 and -10 °C.
In a last step we compared the relationship between ice-containing clouds and temperature of the Leipzig dataset with a similar data set from Cape Verde (15 °N, 23.5 °W). Even though dust is omnipresent in the troposphere at this location, the study of more than 200 spatially well-defined altocumulus clouds did not show a significant number of ice clouds at temperatures above -15 °C.
Possible explanations for the observed differences between the Leipzig and the Cape Verde data set are contrasts in atmospheric dynamics over Central Europe and western Africa or the presence of anthropogenic aerosol over Europe that may provide additional effective ice nuclei besides Saharan dust.
|
45 |
A influência da deposição atmosférica da poeira mineral da Patagônia na biomassa fitoplanctônica do setor Atlântico do Oceano Austral / The inlfuence of Patagonian mineral dust deposiion on phytoplanktonic biomass of the Atlantic Sector of the Southern OceanAlexandre Castagna Mourão e Lima 17 June 2013 (has links)
Conselho Nacional de Desenvolvimento Científico e Tecnológico / O Oceano Austral é a região oceânica de maior extensão em que os
macronutrientes necessários à produção primária permanecem em níveis elevados
por todo ano. Essa condição é conhecida como High Nutrient Low Clorophyll (HNLC)
e é determinada, em grande parte, pela relativa escassez de micronutrientes,
particularmente o ferro. Diversos experimentos comprovaram que a entrada de ferro
neste sistema intensifica a produção biológica, aumentando a fixação do carbono e,
eventualmente, sua exportação para águas profundas. Este fenômeno recebeu
muita atenção nos últimos 20 anos devido a sua possível influencia no clima, via
ciclo do carbono. A relação inversa entre concentração de CO2 na atmosfera e o
fluxo de poeira mineral observados em registros glaciais da Antártica Central sugere
que a deposição atmosférica pode ser uma importante via para o aporte de
micronutrientes. Porém, a contribuição da deposição de poeira mineral para a
produção primária nesta região permanece para ser demonstrada e seu possível
papel no sistema climático ainda não é conclusivo. No caso do setor Atlântico do
Oceano Austral, que recebe influência da Patagônia, os baixos fluxos modernos de
poeira mineral e a baixa solubilidade do ferro associado à estrutura dos alumíniossilicato
levam muitos autores a postular que fontes oceânicas de micronutrientes
sejam mais determinantes. Faltam, no entanto, evidências experimentais. Neste
trabalho, abordamos o estudo da fertilização do setor Atlântico do Oceano Austral
pela poeira da Patagônia utilizando duas ferramentas: (1) o sensoriamento remoto
orbital de aerossóis minerais e clorofila-a em escala interanual; e (2) um experimento
de fertilização, com poeira da Patagônia, realizado na Passagem de
Drake, considerando fluxos estimados para a era moderna e para o último glacial.
Após doze dias de bioensaio, os tratamentos de adição de poeira mostraram a
elevação da clorofila-a e da abundância de células em níveis acima dos controles.
Níveis intermediários e maiores de adição não diferiram entre si na intensidade de
resposta biológica, separando-se apenas da menor adição. Esses resultados
indicam que a poeira da Patagônia, mesmo nos fluxos atuais, é capaz de prover os
micronutrientes escassos na coluna dágua, com potencial para deflagrar aumentos
significativos de biomassa. Através da análise por sensoriamento remoto,
identificamos uma região de alta correlação entre poeira e clorofila-a, que está
localizada entre a Frente Subtropical e a Frente Polar, se estendendo da Argentina
ao sul da África. Esta região difere das águas ao sul da Frente Polar pela menor
profundidade da camada de mistura, menor concentração de silicatos, baixa
biomassa de diatomáceas e, estima-se, maior estresse fisiológico devido à escassez
de ferro e menor aporte oceânico deste nutriente. Em conjunto, essas características
parecem criar condições que tornam a resposta biológica mais sensível à deposição
de poeira mineral. Estes resultados lançam nova luz sobre o controle atual da
produção primária na região e sobre a hipótese da regulação climática pelo
fitoplâncton no Oceano Austral, mediado pela deposição de poeira da Patagônia. / The Southern Ocean is the larger ocean region where the macronutrients
needed for primary production remain in high levels through the year. This condition
is known as High Nutrient Low Chlorophyll (HNLC) and is conditioned, largely, by the
relative shortage of micronutrients, particularly iron. Several experiments proved that
the supply of iron to this system enhances biological production, increasing carbon
fixation and, eventually, its exportation to deep waters. This phenomenon received
much attention in the last 20 years due to its possible influence in the climate,
through carbon cycle. The inverse relationship between the atmospheric CO2
concentration and the mineral dust flux observed on the Central Antarctic glacial
records suggest that atmospheric deposition may be an important source for the
supply of micronutrients. However, the contribution of mineral dust deposition for the
primary production in this region remains to be demonstrated and its possible hole in
the climate system its not yet conclusive. In the case of Atlantic Southern Ocean,
thats influenced by Patagonia, the low modern flows of mineral dust and the low iron
solubility associated with aluminum-silicate structure led many authors to state that
oceanic sources of micronutrients are more determinants. However, experimental
evidence are lacking. In the present work, we approach the study of fertilization of
Atlantic Southern Ocean by Patagonian dust employing two different tools: (1) orbital
remote sensing of mineral aerosols and chlorophyll-a on inter-annual scale; and (2) a
fertilization experiment with Patagonian dust, carried through in Drake Passage,
considering estimated flux for the modern era and for the last glacial. After twelve
days of bioassay, the dust addition treatments showed increase on chlorophyll-a and
cell abundance beyond controls levels. Intermediary and higher levels of addition
didnt differ between each other regarding the intensity of biological response,
separating only of the lower addition treatment. These results indicate that even
modern Patagonia dust flux is capable of providing micronutrients that are scarce in
the water column, with potential to deflagrate a bloom. Through remote sensing
analysis we have identified a region with high correlation between dust and
chlorophyll-a, thats located between the Subtropical Front and the Polar Front,
extending from Argentina to south of Africa. This region differs from waters south of
the Polar Front by means of a deeper mixed layer, lower silicate concentrations, low
diatom biomass and, is estimated, greater iron physiological stress and lower iron
oceanic supply. Together, these properties seem to create conditions to which
biological response would be more sensible to dust deposition. These results cast
new light over controls on modern primary production in the region and over the
phytoplankton climatic regulation in the Southern Ocean, mediated by Patagonian
dust deposition.
|
46 |
Immersion freezing experiments of biological, mineral dust and dust-bio-mixed particles with the Leipzig Aerosol Cloud Interaction SimulatorBauditz, Stefanie 13 December 2017 (has links)
Eiskristalle fördern die Bildung von Niederschlag und beeinflussen die optischen
Eigenschaften einer Wolke. Damit spielen sie eine maßgebliche Rolle für das Wetter und Klima unseres Planeten. In der Atmosphäre entstehen Eiskristalle entweder durch homogene oder durch heterogene Eisnukleation. Letzteres wird durch ein sogenanntes eisnukleierendes Partikel (INP) katalysiert. Bisher ist nur wenig über die speziellen Eigenschaften eines INP bekannt und die Vorhersagbarkeit über die Eisnukleationsfähigkeit verschiedener Materialien
ist somit stark limitiert. Im Rahmen dieser Arbeit wurde das Immersionsgefrierverhalten von Birkenpollen, verschiedenen Mineralstäuben sowie Mischungen aus Mineralstaub und Birkenpollen Material untersucht. Ziel dieser Untersuchungen war, das Gefrierverhalten der verschiedenen Substanzen zu quantifizieren sowie deren Bedeutung für die Atmopshärische
Eisnukleation besser zu verstehen. Das Gefrierverhalten eisaktiver Birkenpollen Makromoleküle konnte in dieser Arbeit erstmals unter atmosphärisch relevanten Bedingungen quantifiziert werden. Ein Vergleich zweier Birkenpollen Proben mit unterschiedlicher Herkunft demonstrierte die Abhängigkeit der Gefriereigenschaften der Birkenpollen von der geografischen
Breite. Es wurden zwei unterschiedlich eisaktive Makromoleküle identifiziert, welche
beide bei Temperaturen oberhalb −20°C aktiv sind. Das Gefrierverhalten unterschiedlicher Mineralstaubpartikel wurde hinsichtlich ihres K-Feldspat Anteils verglichen. Dabei zeigte sich, dass der K-Feldspat Anteil das Gefrierverhalten der Mineralstaubpartikel kontrolliert. Außerdem konnte gezeigt werden, dass eine Beschichtung mit Schwefelsäure die Eiskeimfähigkeit von K-Feldspat stark herabsetzt. In der Atmosphäre sind Partikel, welche sowohl aus
mineralischen als auch aus biologischen Komponenten bestehen sehr wahrscheinlich. Um zu demonstrieren wie sich ein Mineralstaubpartikel verhält, wenn es mit biologischem Material gemischt wird, wurde in dieser Arbeit das Gefrierverhalten von Mischpartikeln bestehend aus Illit-NX und Birkenpollen Material untersucht. Es konnte gezeigt werden, dass die eisaktiven
Makromoleküle der Birkenpolle ihre Eisaktivität beibehalten, auch wenn sie an einem Illit- NX Partikel angelagert sind. Die Mischpartikel zeigen somit das selbe Gefrierverhalten, wie reine Birkenpollen Partikel. Dies zeigt die bisher unterschätzte Bedeutung von biologischem Material für die atmosphärische Eisnukleation. / It is known that ice crystals in clouds play an important role for climate and
weather as they influence precipitation initiation and radiative forcing. Ice formation in clouds occurs either through homogeneous or heterogeneous ice nucleation. For the latter case an ice nucleating particle (INP) catalyzes the freezing process. The knowledge about the properties which make a particle act as efficient INP is still limited. As a consequence, the ice nucleation ability of different materials has to be examined by quantitative experimentation. In the framework of the present thesis, the immersion freezing behavior of birch pollen material, different mineral dust particles and internal mixtures of mineral dust and birch pollen material was studied to improve our understanding of the importance of these species for the atmospheric ice nucleation. A quantification of the freezing behavior of ice nucleating active (INA) birch pollen macromolecules under atmospherically relevant conditions was done for the first time. Furthermore, the freezing ability of two birch pollen samples with different local origin was compared. It could be shown that birch pollen are able to produce at least two different types of INA macromolecules, which are both ice active in a temperature regime above −20◦ C. It became obvious that one of the macromolecules is favorably produced in higher latitudes, which indicated the dependence of the freezing properties of birch pollen
from their local origin. Concerning mineral dust particles the present thesis demonstrated that the freezing ability of different K-feldspar containing mineral dust proxys like Arizona test dust, kaolinite and illite-NX, is controlled by their K-feldspar content. Furthermore, it was shown that K-feldspar loses its good freezing ability after surface modification with sulfuric acid. As internal mixtures of mineral and biological components are very likely in the atmosphere, the freezing ability of such mixed particles has been investigated in the present thesis. For illite-NX particles which were mixed with birch pollen material, it could be shown
that the birch pollen macromolecules maintain their freezing ability when being adsorbed to a mineral dust particle. As a result, the affected mineral dust particle initiates freezing exactly like a birch pollen particle. For atmospheric application this means that it is likely that the ascription of mineral dust to the atmospheric INPs is, at least to a certain extent, due to unnoticed attached ice nucleating biological material.
|
47 |
Die Adsorption von Lipoproteinen an der Oberfläche fibrogener und inerter MineralstäubeBogatu, Bettina Ulrike 14 June 2004 (has links)
Sieben fibrogene und fünf nicht fibrogene (inerte) Mineralstäube wurden auf ihr Adsorptionsvermögen gegenüber Lipoproteinen untersucht. Die Adsorption erfolgte aus menschlichem Serum bzw. bovinem Lipoproteinkonzentrat. Die spezifischen Oberflächen der Stäube wurden mit Hilfe einer neuen Methode ermittelt, die auf der Adsorption von Nonadecansäure beruht. Sie vernachlässigt Oberflächenporen mit Öffnungsdurchmessern / Seven fibrogenic and five nonfibogenic (inert) mineral dusts were examined for their adsorption capacity for lipoproteins. Lipoproteins came from human serum and bovine lipoprotein- concentrate. The specific surface areas of the dusts were determined with the help of a new method, which is based on the adsorption of nonadecanoic acid. It neglects surface pores with opening diameters less than 2,5nm. The most important result is that fibrogenic dusts adsorb significantly more high density lipoproteins (HDL), than the inert dusts. The adsorption of HDL on quartz can be reduced up to 96% by addition of Polyvinylpyridine-N-oxide (PVPNO), an inhibitor of quartz- induced fibrosis. The HDL- adsorption might play a role during the developing process of mineral-dust-induced fibrosis.
|
48 |
Understanding Atmospheric Mineral Dust Photochemistry / Étude des propriétés photocatalytiques des poussières minéralesPonczek, Milena 15 October 2018 (has links)
Les minéraux absorbent la lumière proche des UV (comme TiO2, Fe2O3, MgO) présents dans les aérosols minéraux interagissent avec les gaz traces présents dans l'atmosphère et peuvent initier une nouvelle chimie hétérogène photo-induite potentiellement significative et actuellement peu documentée. Cette thèse vise à aborder différentes questions sur la réactivité des poussières minérales vers les composés organiques et évaluer l'impact de ces interactions sur plusieurs aspects des sciences de l'atmosphère. Nous avons étudié expérimentalement l'interaction physico-chimique d'aérosols minéraux, purs ou revêtus de matériaux organiques/inorganiques avec des gaz traces de plusieurs familles chimiques (alcools, cétones, acides carboxyliques), dans des conditions simulées proches de l'environnement reel (concernant l'humidité, la concentration en phase gazeuse, la longueur d'onde et l'intensité de l'irradiation, la pression et la température) évaluant les effets des conditions ambiantes sur la cinétique de capture et la génération de produits en phase gazeuse. Dans l'ensemble, nos résultats montrent clairement que les reactions photochimique des poussières minérales doit être considéré comme une source de composés réactifs et comme un processus clé affectant leur action sur la nucléation de la glace et les noyaux de condensation des nuages / Minerals that absorb light near UV/Vis present in dust aerosols interact with trace gases in the atmosphere and can initiate a new and potentially significant photo-induced heterogeneous chemistry, which is currently poorly documented. This thesis aims to address different issues of mineral dust reactivity towards organic compounds and, therefore, assesses the impact of these interactions on several aspects of atmospheric sciences. We investigated experimentally the physicochemical interaction of mineral aerosols (synthetic and natural), pure or coated with organic/inorganic materials with trace gases from several chemical families (alcohols, ketones, carboxylic acids, etc.), under simulated conditions close to the real environment (regarding to humidity, concentration in the gas phase, wavelength and intensity of irradiation, pressure and temperature). In a first approach, we studied the uptake of oxygenated organics onto different dust proxies such as SiO2, TiO2 and Arizona test dust (ATD) evaluating the effects of ambient conditions on the uptake kinetics and product generation. Then, we discussed the chemistry of 5 dicarboxylic acids (C4-C8) on ATD particles upon UV-A irradiation monitoring products in the gas phase as well as those whose stay adsorbed on the particulate phase. Lastly, we investigated the influence of nitrate anions on the uptake of acetone on ATD and SiO2 and in the photochemical product formation of glutaric acid on ATD. Overall, our results clearly show that photochemical processing of dust aerosols should be considered as a source of reactive compounds and as a key process affecting their action as ice nucleation and cloud condensation nuclei
|
49 |
Dust-related ice formation in the troposphere: A statistical analysis based on 11 years of lidar observations of aerosols and clouds over LeipzigSeifert, Patric 14 December 2010 (has links)
Im Rahmen der vorliegenden Arbeit wurde der Zusammenhang zwischen heterogener Eisbildung und Temperatur auf Basis eines 11-Jahres Lidardatensatzes untersucht, wobei besonders der potenzielle Einfluss von Wüstenstaubaerosol auf die heterogene Gefriertemperatur von unterkühlten Wasserwolken überprüft wurde. Der zugrundeliegende Lidardatensatz entstand im Rahmen von zwischen 1997 und 2008 am Leibniz-Institut für Troposphärenforschung (IfT) in Leipzig durchgeführten Lidarmessungen. Mehr als 2300 zeitlich und räumlich defifinierte Wolkenschichten wurden anhand des gemessenen linearen Depolarisationsverhältnisses als Flüssigwasserwolken oder als eisbeinhaltende Wolken klassifiziert. Dazu war es nötig, den störenden Einfluss von spiegelnden Reflektionen horizontal ausgerichteter Eiskristalle auf das gemessene Depolarisationsverhältnis zu charakterisieren. Die für die Auswertung benötigten Wolkenoberkantentemperaturen wurden aus Modelldaten oder, falls zeitnah verfügbar, aus Radiosondenprofifilen ermittelt.
Die statistische Auswertung des Wolkendatensatzes ergab, dass der Anteil an eisbeinhaltenden Wolken mit abnehmender Temperatur stark zunimmt. Wurde in Wolken mit Oberkantentemperaturen zwischen 0 und -5 °C in nur 1% aller Fälle Eis detektiert, enthielten zwischen -10 und -15 °C bereits 40% der in dem Temperaturbereich beobachteten Wolken Eis. Bei Wolkenoberkantentemperaturen unterhalb von -25 °C wurde in nahezu 100% aller Fälle Eis in den Wolken beobachtet. Ein ähnlicher Zusammenhang zwischen Temperatur und dem Anteil an eisbeinhaltenden Wolken wurde bereits in zahlreichen auf Flugzeugmessungen basierenden Studien gefunden.
In einem weiteren Schritt wurde der Wolkendatensatz mittels drei verschiedener Ansätze in einen staubbelasteten sowie einen staubfreien Teil getrennt. Dies geschah Anhand einer Trajektorien-Clusteranalyse sowie der Trennung bezüglich der von einem Mineralstaubvorhersagemodell berechneten Mineralstaubbelastung in Wolkenhöhe beziehungsweise in der gesamten Luftsäule über Leipzig. Die Trennung ergab, dass staubbelastete Wolken im Temperaturbereich zwischen -5 und -25 °C 10-30% mehr Eis beinhalten als staubfreie Wolken. Die Ergebnisse dieser Untersuchung legen deshalb nahe, dass Mineralstaub Eisbildung in unterkühlten Wolken maßgeblich fördert.
Der Vergleich des Leipziger Wolkendatensatzes mit einem auf den Kapverden gesammelten Datensatz tropischer Wolken zeigte, dass trotz vergleichbarem Einfluss von Mineralstaubaerosol Eisbildung in den Tropen erst bei um 10 K tieferen Temperaturen einsetzt. Als mögliche Einflussfaktoren wurden Unterschiede in der atmosphärischen Dynamik und die Wirkung effektiverer Eiskeime über Mitteleuropa diskutiert.:1 Introduction
2 Ice formation
2.1 Homogeneous nucleation
2.2 Heterogeneous nucleation
2.2.1 Heterogeneous nucleation processes
2.2.2 Studies of heterogeneous nucleation
2.3 Dynamical processes and ice multiplication
3 Motivating questions for the present study
4 IfT Earlinet lidar MARTHA
4.1 IfT lidar system MARTHA
4.2 Lidar equation
4.3 Particle backscatter coefficient
4.3.1 Klett-Fernald method
4.3.2 Raman method
4.4 Particle extinction coefficient
4.5 Depolarization ratio
4.5.1 Depolarization ratio for idealized systems
4.5.2 Depolarization ratio for non-idealized systems
5 Cloud detection with MARTHA
5.1 Cloud geometrical properties
5.2 Meteorological data
5.3 Aerosol information
5.4 Cloud phase determination
5.5 Multiple scattering
5.6 Specular reflection
5.6.1 Instrumentation
5.6.2 WiLi and MARTHA observations
5.6.3 PollyXT and MARTHA observations
5.7 Liquid/Ice-containing layer discrimination scheme for MARTHA
6 Observations
6.1 20 June 2007: Cloud development in Saharan dust
6.2 3 November 2003 and 24 November 2006: Cloud development at aerosol background conditions
6.3 26 May 2008 and 26 December 2008: Indications for deposition nucleation
7 The MARTHA 1997-2008 cloud data set
7.1 Statistical basis
7.2 Geometrical cloud properties
7.3 Relationship between heterogeneous ice formation and temperature
7.4 Impact of Saharan dust on heterogeneous ice nucleation
7.4.1 Trajectory cluster analysis
7.4.2 Dust-model-based investigations
7.5 Discussion
8 Summary, conclusions, and outlook
8.1 Summary and conclusions
8.2 Outlook
Bibliography
List of abbreviations / The formation and presence of ice crystals in clouds strongly determines meteorological processes as precipitation formation but also climatological parameters as the radiation budget of the atmosphere. The process of ice formation, however, is not straightforward because ice crystals and liquid water droplets can coexist at temperatures from -38 °C to 0 °C. In this temperature range, aerosol particles, so-called ice nuclei, must be present to trigger ice formation in a supercooled droplet.
From laboratory studies it is known that mineral dust particles are efficient ice nuclei. We present a statistical analysis of lidar-based observations of 2300 free-tropospheric clouds that was used to investigate the effect of mineral dust particles on the ice-formation temperature. The observations were performed at Leipzig, Germany (51° N, 12 °E). The time and height as well as the phase state (ice, liquid-water) of the observed clouds can easily be derived from the lidar data. The dust load in every observed cloud layer was determined by means of model data.
From the analysis it was found that dust-affected clouds produce ice 50% more frequently than dust-free clouds at temperatures between -20 and -10 °C.
In a last step we compared the relationship between ice-containing clouds and temperature of the Leipzig dataset with a similar data set from Cape Verde (15 °N, 23.5 °W). Even though dust is omnipresent in the troposphere at this location, the study of more than 200 spatially well-defined altocumulus clouds did not show a significant number of ice clouds at temperatures above -15 °C.
Possible explanations for the observed differences between the Leipzig and the Cape Verde data set are contrasts in atmospheric dynamics over Central Europe and western Africa or the presence of anthropogenic aerosol over Europe that may provide additional effective ice nuclei besides Saharan dust.:1 Introduction
2 Ice formation
2.1 Homogeneous nucleation
2.2 Heterogeneous nucleation
2.2.1 Heterogeneous nucleation processes
2.2.2 Studies of heterogeneous nucleation
2.3 Dynamical processes and ice multiplication
3 Motivating questions for the present study
4 IfT Earlinet lidar MARTHA
4.1 IfT lidar system MARTHA
4.2 Lidar equation
4.3 Particle backscatter coefficient
4.3.1 Klett-Fernald method
4.3.2 Raman method
4.4 Particle extinction coefficient
4.5 Depolarization ratio
4.5.1 Depolarization ratio for idealized systems
4.5.2 Depolarization ratio for non-idealized systems
5 Cloud detection with MARTHA
5.1 Cloud geometrical properties
5.2 Meteorological data
5.3 Aerosol information
5.4 Cloud phase determination
5.5 Multiple scattering
5.6 Specular reflection
5.6.1 Instrumentation
5.6.2 WiLi and MARTHA observations
5.6.3 PollyXT and MARTHA observations
5.7 Liquid/Ice-containing layer discrimination scheme for MARTHA
6 Observations
6.1 20 June 2007: Cloud development in Saharan dust
6.2 3 November 2003 and 24 November 2006: Cloud development at aerosol background conditions
6.3 26 May 2008 and 26 December 2008: Indications for deposition nucleation
7 The MARTHA 1997-2008 cloud data set
7.1 Statistical basis
7.2 Geometrical cloud properties
7.3 Relationship between heterogeneous ice formation and temperature
7.4 Impact of Saharan dust on heterogeneous ice nucleation
7.4.1 Trajectory cluster analysis
7.4.2 Dust-model-based investigations
7.5 Discussion
8 Summary, conclusions, and outlook
8.1 Summary and conclusions
8.2 Outlook
Bibliography
List of abbreviations
|
50 |
Radiative Effect of Mixed Mineral Dust and Biomass Burning Aerosol in the Thermal InfraredKöhler, Claas H. 13 December 2013 (has links)
This thesis treats the optical properties of mixed mineral dust and biomass burning aerosol in the thermal infrared (TIR) based on Fourier Transform infrared spectrometer (FTIR) measurements and radiative transfer simulations. The measurements were part of the Saharan Mineral Dust Experiment 2 (SAMUM-2) conducted from January to February 2008 at Praia, Cape Verde. The large amount of different instruments co-located at the main field site during the campaign resulted in a unique dataset comprising in-situ information and remote sensing data perfectly suited for column closure studies. The ultimate goal of this work is to investigate the consistency of microphysical and TIR remote sensing data. This is achieved by reproducing the measured radiances at top and bottom of the atmosphere (TOA, BOA) with a radiative transfer model, which assimilates the microphysical aerosol information gathered during SAMUM-2.
The first part of the thesis describes several experimental efforts, including a novel calibration method and a drift correction algorithm for the ground-based FTIR instrument operated within the scope of SAMUM-2 by the author. The second part introduces the concurrent radiative transfer library PIRATES, which has been developed in the framework of this thesis for the analysis of TIR aerosol optical properties. The third and final part of the treatise compares measured and simulated spectra for various typical scenarios encountered during SAMUM-2.
It is demonstrated in three case studies, that measured radiances in the TIR atmospheric window region (8-12 µm) can be reproduced at BOA and TOA by radiative transfer simulations assuming spheroidal model particles. Moreover,
spherical particles are shown to be an inadequate model for mineral dust aerosol
in this spectral region unless the aerosol optical depth is small.
|
Page generated in 0.0887 seconds