This dissertation deals with spectral measurements of solar radiation in the visible and near infrared wavelength range. The data were collected during a field campaign on the Cape Verde Islands in January / February 2008 within the DFG research group SAMUM 2 (Saharan Mineral Dust Experiment). During this campaign airborne measurements of upward radiances and irradiances were performed over aerosol layers. Since the Cape Verde Islands are in the advection area of air masses from the Sahara region northeast of the islands and from regions with bush fires from the southeast, the sampled aerosol mainly consists of mineral dust, biomass burning smoke or a mixture of both. These radiation measurements and airborne lidar measurements of aerosol extinction coefficients were used to calculate the dust radiative forcing at the top of atmosphere with an one-dimensional radiative transfer model. This required the spectral surface albedo and aerosol optical properties, determined by model retrievals. The dependence of the calculated dust radiative forcing on the aerosol optical thickness was used to distinguish between aerosol distributions with mineral dust only or mixed with biomass burning smoke. This mainly model-based method was compared with another mainly measurement-based method, which requires the net radiation at the flight altitude and its dependence on the aerosol optical thickness to distinguish between the different aerosol distributions. The mainly model-based method shows no differences between the calculated radiative forcings of aerosols mainly consisting of mineral dust and those mixed with biomass burning smoke due to high uncertainties. In contrast to the mainly model-based method, the mainly measurement-based method shows clear differences between aerosols with and without biomass burning smoke. Thus the mainly measurement-based method is the preferred method, because it omits the retrieval of the aerosol optical properties, which leads to high uncertainties, in contrast to the mainly model-based method.

The Arctic large-scale circulation is governed by a wide range of factor. In order to investigate the sensitivity of the Arctic large-scale circulation to the regional radiative forcing over Europe, we conducted sensitivity experiments using a state-of-the-art atmosphere-land-ocean coupled model. Using advanced Deep Learning (DL) algorithms, we analyzed the Arctic circulation regimes response to negative radiative forcing anomalies over Europe. We examined different architectures for our DL algorithm to find the most suitable one for our analysis. We simultaneously layer Thickness (300-700-T) and their spatiotemporal patterns with the DL algorithm. The DL algorithm showed good skills in capturing the general structure of the large-scale circulation. The radiative forcing over Europe doesn't seem to induce the occurrence frequency of preferred circulation regimes. / Die arktische großräumige Zirkulation wird von einer Vielzahl von Faktoren bestimmt. Um die Sensitivität der arktischen großräumigen Zirkulation auf den regionalen Strahlungsantrieb über Europa zu untersuchen, haben wir Sensitivitätsexperimente mit einem hochmodernen gekoppelten Atmosphäre-Land-Ozean-Modell untersucht. Unter Verwendung neuer Deep-Learning-Algorithmen (DL) analysierten wir die Reaktion der arktischen Zirkulationsregime auf negativen Strahlungsantriebsanomalien über Europa. Wir haben verhsciedene Architekturen für unseren DL-Algorithmus untersucht, um die am besten geeignete für unsere Analyse zu finden. Wir haben die Felder des mittleren Drucks auf Meeresspiegelniveau und der Schichtdicke von 700 bis 300 hPa und ihre raumzeitlichen Muster mit dem DL-Algorithmus analysiert. Die DL-Algorithmen zeigten gute Ergebnisse bei der Erfassung der allgmeinen Struktur der großräumigen Zirkulation. Der Strahlungsantrieb über Europa scheint der großräumigen Zirkulation keine neuen raumzeitlichen Muster zuzufügen, veränderte aber die Häufigkeit des Auftretens bevorzugter Zirkulationsmuster.

Soot particles are a major absorber of shortwave radiation in the atmosphere. They exert a rather uncertain direct and semi-direct radiative effect, which causes a heating or in some cases a cooling of the atmosphere. The mass absorption coefficient is an essential quantity to describe this light absorption process. This work presents new experimental data on the mass absorption coefficient of soot particles in the troposphere over Central Europe. Mass absorption coefficients were derived as the ratio between the light absorption coefficient determined by multi angle absorption photometry (MAAP), and the soot mass concentration determined by Raman spectroscopy. The Raman method is sensitive to graphitic structures present in the particle samples, and was calibrated in the laboratory using Printex90 model particles. The mass absorption coefficients were determined for a number of seven observation sites, ranging between 3.9 and 7.4 m²/g depending on measurement site and observational period. The highest values were found in an continentally aged air mass in winter, where we presumed soot particles to be present mainly in internal mixture. The regional model WRF-Chem was used in conjunction with a high resolution soot emission inventory to simulate soot mass concentrations and absorption coefficients for the Central European Troposphere. The model was validated using soot mass concentrations from Raman measurements and absorption coefficients. Simulated soot mass concentrations were found to be too low by around 50 %, which could be improved by scaling the emissions by a factor of two. In contrast, the absorption coefficient was positively biased by around 20%. Adjusting the modeled mass absorption coefficient to measurements, the simulation of soot light absorption was improved. Finally, the positive direct radiative forcing at top of the atmosphere was found to be lowered by up to 70% for the model run with adjusted soot absorption behaviour, , indicating a decreased heating effect on the atmosphere.

This dissertation deals with spectral measurements of solar radiation in the visible and near infrared wavelength range. The data were collected during a field campaign on the Cape Verde Islands in January / February 2008 within the DFG research group SAMUM 2 (Saharan Mineral Dust Experiment). During this campaign airborne measurements of upward radiances and irradiances were performed over aerosol layers. Since the Cape Verde Islands are in the advection area of air masses from the Sahara region northeast of the islands and from regions with bush fires from the southeast, the sampled aerosol mainly consists of mineral dust, biomass burning smoke or a mixture of both. These radiation measurements and airborne lidar measurements of aerosol extinction coefficients were used to calculate the dust radiative forcing at the top of atmosphere with an one-dimensional radiative transfer model. This required the spectral surface albedo and aerosol optical properties, determined by model retrievals. The dependence of the calculated dust radiative forcing on the aerosol optical thickness was used to distinguish between aerosol distributions with mineral dust only or mixed with biomass burning smoke. This mainly model-based method was compared with another mainly measurement-based method, which requires the net radiation at the flight altitude and its dependence on the aerosol optical thickness to distinguish between the different aerosol distributions. The mainly model-based method shows no differences between the calculated radiative forcings of aerosols mainly consisting of mineral dust and those mixed with biomass burning smoke due to high uncertainties. In contrast to the mainly model-based method, the mainly measurement-based method shows clear differences between aerosols with and without biomass burning smoke. Thus the mainly measurement-based method is the preferred method, because it omits the retrieval of the aerosol optical properties, which leads to high uncertainties, in contrast to the mainly model-based method.

Persistent condensation trails are clouds, induced by the exhaust of an aircraft engine in a cold and ice-supersaturated environment. These artificial ice clouds can both cool and heat the atmosphere by scattering solar radiation and absorbing terrestrial radiation, respectively. The influence of condensation trails on the Earth-atmosphere energy balance and therewith the answer to the question of the dominating process had been mostly approximated on a global scale by treating the condensation trail as plane parallel layer with constant optical properties. Individual condensation trails and the influence of the solar angle had been analyzed, always using a course spatial grid and never under consideration of the aircraft performance, generating the condensation trail. For a trajectory optimization, highly precise results of the impact of condensation trails on the radiation budget and the influence of the aircraft performance on this impact is needed, so that future air traffic may consider the main factors of flight performance on the environmental impact of condensation trails. That’s why, a model is developed in this thesis to continuously estimate the scattering and absorption properties and their dependence on the aircraft performance. / Langlebige Kondensstreifen sind Eiswolken, welche durch Kondensation von Wasserdampf an Rußpartikeln in einer eisübersättigten Atmosphäre entstehen. Der Wasserdampf entstammt einerseits aus dem Triebwerkabgas und andererseits aus der Atmosphäre. Kondensstreifen können die Atmosphäre durch Rückstreuung solarer Strahlung kühlen und durch Rückstreuung und Absorption terrestrischer Strahlung erwärmen. Der Einfluss von Kondensstreifen auf den Wärmehaushalt der Atmosphäre und damit die Antwort auf die Frage nach dem dominierenden Effekt wurde bisher zumeist auf globaler Ebene ermittelt, wobei der Kondensstreifen als planparallele Schicht mit konstanten optischen Eigenschaften angenähert wurde. Individuelle Kondensstreifen und der Einfluss des Sonnenstandes wurden bisher nur mithilfe eines groben Rasters betrachtet und niemals unter Berücksichtigung der Flugleistung des Luftfahrzeuges, welches den Kondensstreifen generiert hat. Für eine Trajektorienoptimierung sind jedoch präzise Berechnungen des Strahlungseinflusses und eine gewissenhafte Berücksichtigung der Flugleistung notwendig. Nur so kann der zukünftige Luftverkehr die Haupteinflussfaktoren der Flugeigenschaften auf den Strahlungseinfluss der Kondensstreifen berücksichtigen. Aus diesem Grund wurde in dieser Arbeit ein Modell entwickelt, welches die Eigenschaften des Strahlungstransfers durch den Kondensstreifen kontinuierlich bestimmt und die aus der Flugleistung resultierenden Parameter berücksichtigt.

Persistent condensation trails are clouds, induced by the exhaust of an aircraft engine in a cold and ice-supersaturated environment. These artificial ice clouds can both cool and heat the atmosphere by scattering solar radiation and absorbing terrestrial radiation, respectively. The influence of condensation trails on the Earth-atmosphere energy balance and therewith the answer to the question of the dominating process had been mostly approximated on a global scale by treating the condensation trail as plane parallel layer with constant optical properties. Individual condensation trails and the influence of the solar angle had been analyzed, always using a course spatial grid and never under consideration of the aircraft performance, generating the condensation trail. For a trajectory optimization, highly precise results of the impact of condensation trails on the radiation budget and the influence of the aircraft performance on this impact is needed, so that future air traffic may consider the main factors of flight performance on the environmental impact of condensation trails. That’s why, a model is developed in this thesis to continuously estimate the scattering and absorption properties and their dependence on the aircraft performance.:1 Introduction 3 1.1 Motivation 3 1.2 State of the art 5 1.3 Approach 6 2 Theoretical background 9 2.1 The Earth’s atmosphere 9 2.1.1 The mean vertical structure of the atmosphere 12 2.1.2 Standard atmospheres 14 2.2 Radiation 15 2.2.1 Nature of radiation 15 2.2.2 Important metrics describing radiation 17 2.2.3 Relevant spectra and principles of radiation 19 2.2.4 Solar radiation 20 2.2.5 Terrestrial radiation 21 2.2.6 Radiative transfer and extinction 22 2.2.7 Radiative transfer equation 30 2.2.8 Energy budget of the Earth-atmosphere system 32 2.3 Thermodynamics 33 2.3.1 Atmospheric stability 33 2.3.2 Turbulence 36 2.3.3 Conditions of contrail formation 41 3 Development of a radiative forcing model 45 3.1 Model atmosphere 45 3.2 Flight performance model 46 3.3 Atmospheric radiative transfer model 49 3.3.1 Two Stream Approximation 51 3.3.2 Discrete ordinate radiative transfer solver 52 3.3.3 Methods to calculate broadband radiances and irradiances 53 3.4 Contrail life cycle model 57 3.4.1 Dissipation regime 58 3.4.2 Diffusion regime 63 3.5 Contrail radiative forcing model 74 3.5.1 Consideration of multiple scattering using a Monte Carlo simulation 74 3.5.2 Geometry of the Monte Carlo simulation 75 3.5.3 Interpretation of Beer’s law 76 3.5.4 Procedure of the Monte Carlo simulation 79 3.5.5 The extinguished power per unit length contrail 87 3.5.6 Scattering and absorption efficiencies Qs, Qa and asymmetry parameters gHG 89 3.5.7 Calibration of the Monte Carlo simulation 94 4 Calculations 99 4.1 Contrail properties 99 4.1.1 Conditions of contrail formation 100 4.1.2 Initial dimensions at the end of the dissipation regime 101 4.1.3 Microphysical properties during the diffusion regime 103 4.2 Radiative transport up to the contrail 105 4.2.1 Solar direct and diffuse radiance 106 4.2.2 Terrestrial irradiance 107 4.3 Scattering and absorption properties of radiation within the contrail 109 4.3.1 Monte Carlo simulation for solar radiation 109 4.3.2 Monte Carlo simulation for terrestrial irradiances 112 4.3.3 Relevance of multiple scattering 116 4.4 Radiative extinction 116 4.4.1 Solar zenith and azimuthal angle 118 4.4.2 Flightpath 120 4.4.3 Contrail evolution 122 4.4.4 Turbulence 126 4.4.5 Wavelength specific extinction 129 4.5 Terrestrial energy forcing of a contrail 133 4.6 Verification 135 5 Conclusion and outlook 141 5.1 Conclusion 141 5.2 Outlook 144 List of Figures 147 List of Tables 151 Abbreviations and Symbols 153 Glossary 161 Bibliography 169 Acknowledgements 183 / Langlebige Kondensstreifen sind Eiswolken, welche durch Kondensation von Wasserdampf an Rußpartikeln in einer eisübersättigten Atmosphäre entstehen. Der Wasserdampf entstammt einerseits aus dem Triebwerkabgas und andererseits aus der Atmosphäre. Kondensstreifen können die Atmosphäre durch Rückstreuung solarer Strahlung kühlen und durch Rückstreuung und Absorption terrestrischer Strahlung erwärmen. Der Einfluss von Kondensstreifen auf den Wärmehaushalt der Atmosphäre und damit die Antwort auf die Frage nach dem dominierenden Effekt wurde bisher zumeist auf globaler Ebene ermittelt, wobei der Kondensstreifen als planparallele Schicht mit konstanten optischen Eigenschaften angenähert wurde. Individuelle Kondensstreifen und der Einfluss des Sonnenstandes wurden bisher nur mithilfe eines groben Rasters betrachtet und niemals unter Berücksichtigung der Flugleistung des Luftfahrzeuges, welches den Kondensstreifen generiert hat. Für eine Trajektorienoptimierung sind jedoch präzise Berechnungen des Strahlungseinflusses und eine gewissenhafte Berücksichtigung der Flugleistung notwendig. Nur so kann der zukünftige Luftverkehr die Haupteinflussfaktoren der Flugeigenschaften auf den Strahlungseinfluss der Kondensstreifen berücksichtigen. Aus diesem Grund wurde in dieser Arbeit ein Modell entwickelt, welches die Eigenschaften des Strahlungstransfers durch den Kondensstreifen kontinuierlich bestimmt und die aus der Flugleistung resultierenden Parameter berücksichtigt.:1 Introduction 3 1.1 Motivation 3 1.2 State of the art 5 1.3 Approach 6 2 Theoretical background 9 2.1 The Earth’s atmosphere 9 2.1.1 The mean vertical structure of the atmosphere 12 2.1.2 Standard atmospheres 14 2.2 Radiation 15 2.2.1 Nature of radiation 15 2.2.2 Important metrics describing radiation 17 2.2.3 Relevant spectra and principles of radiation 19 2.2.4 Solar radiation 20 2.2.5 Terrestrial radiation 21 2.2.6 Radiative transfer and extinction 22 2.2.7 Radiative transfer equation 30 2.2.8 Energy budget of the Earth-atmosphere system 32 2.3 Thermodynamics 33 2.3.1 Atmospheric stability 33 2.3.2 Turbulence 36 2.3.3 Conditions of contrail formation 41 3 Development of a radiative forcing model 45 3.1 Model atmosphere 45 3.2 Flight performance model 46 3.3 Atmospheric radiative transfer model 49 3.3.1 Two Stream Approximation 51 3.3.2 Discrete ordinate radiative transfer solver 52 3.3.3 Methods to calculate broadband radiances and irradiances 53 3.4 Contrail life cycle model 57 3.4.1 Dissipation regime 58 3.4.2 Diffusion regime 63 3.5 Contrail radiative forcing model 74 3.5.1 Consideration of multiple scattering using a Monte Carlo simulation 74 3.5.2 Geometry of the Monte Carlo simulation 75 3.5.3 Interpretation of Beer’s law 76 3.5.4 Procedure of the Monte Carlo simulation 79 3.5.5 The extinguished power per unit length contrail 87 3.5.6 Scattering and absorption efficiencies Qs, Qa and asymmetry parameters gHG 89 3.5.7 Calibration of the Monte Carlo simulation 94 4 Calculations 99 4.1 Contrail properties 99 4.1.1 Conditions of contrail formation 100 4.1.2 Initial dimensions at the end of the dissipation regime 101 4.1.3 Microphysical properties during the diffusion regime 103 4.2 Radiative transport up to the contrail 105 4.2.1 Solar direct and diffuse radiance 106 4.2.2 Terrestrial irradiance 107 4.3 Scattering and absorption properties of radiation within the contrail 109 4.3.1 Monte Carlo simulation for solar radiation 109 4.3.2 Monte Carlo simulation for terrestrial irradiances 112 4.3.3 Relevance of multiple scattering 116 4.4 Radiative extinction 116 4.4.1 Solar zenith and azimuthal angle 118 4.4.2 Flightpath 120 4.4.3 Contrail evolution 122 4.4.4 Turbulence 126 4.4.5 Wavelength specific extinction 129 4.5 Terrestrial energy forcing of a contrail 133 4.6 Verification 135 5 Conclusion and outlook 141 5.1 Conclusion 141 5.2 Outlook 144 List of Figures 147 List of Tables 151 Abbreviations and Symbols 153 Glossary 161 Bibliography 169 Acknowledgements 183

Soot particles are a major absorber of shortwave radiation in the atmosphere. They exert a rather uncertain direct and semi-direct radiative effect, which causes a heating or in some cases a cooling of the atmosphere. The mass absorption coefficient is an essential quantity to describe this light absorption process. This work presents new experimental data on the mass absorption coefficient of soot particles in the troposphere over Central Europe. Mass absorption coefficients were derived as the ratio between the light absorption coefficient determined by multi angle absorption photometry (MAAP), and the soot mass concentration determined by Raman spectroscopy. The Raman method is sensitive to graphitic structures present in the particle samples, and was calibrated in the laboratory using Printex90 model particles. The mass absorption coefficients were determined for a number of seven observation sites, ranging between 3.9 and 7.4 m²/g depending on measurement site and observational period. The highest values were found in an continentally aged air mass in winter, where we presumed soot particles to be present mainly in internal mixture. The regional model WRF-Chem was used in conjunction with a high resolution soot emission inventory to simulate soot mass concentrations and absorption coefficients for the Central European Troposphere. The model was validated using soot mass concentrations from Raman measurements and absorption coefficients. Simulated soot mass concentrations were found to be too low by around 50 %, which could be improved by scaling the emissions by a factor of two. In contrast, the absorption coefficient was positively biased by around 20%. Adjusting the modeled mass absorption coefficient to measurements, the simulation of soot light absorption was improved. Finally, the positive direct radiative forcing at top of the atmosphere was found to be lowered by up to 70% for the model run with adjusted soot absorption behaviour, , indicating a decreased heating effect on the atmosphere.