In this thesis a new three–dimensional (3D) vector radiative transfer model, the Solver for Polarized Atmospheric Radiative Transfer Applications (SPARTA) is introduced, validated against benchmark results, and applied to scientific problems. SPARTA employs the statistical forward Monte Carlo technique for efficient column–response pixel–based radiance calculations comprising polarization for 3D inhomogeneous cloudless and cloudy atmospheres. By means of SPARTA, two scientific issues in the field of radiative transfer are investigated. A sensitivity study has been conducted to illustrate the errors introduced by neglecting the effects of polarization in radiation simulations. Two atmospheric scenarios have been considered: a pure one–dimensional (1D) Rayleigh atmosphere and two–dimensional (2D) realistic inhomogeneous dust fields. In case of a purely molecular atmosphere, these errors strongly depend on molecular anisotropy, isotropic reflection, and more importantly, on single scattering albedo and optical thickness (saturation occurs for τ close to 1). Overall errors in the reflected field range up to about 10.5%. On the other hand, for rather high optical thickness, the bias induced by ignoring polarization for realistic inhomogeneous atmospheres is negligible (less than 1%). In addition, solar radiative transfer simulations for LIDAR–measured fields of optical properties of Saharan dust have been performed in order to quantify the effects induced by neglecting the horizontal photon transport and internal inhomogeneities (3D radiative effects) in radiance simulations including polarization. Results are presented for two exemplary mineral dust fields constructed from LIDAR observations. For each case, three radiative calculations are investigated: a 1D calculation according to the plane–parallel (1D mode); an Independent Pixel Approximation (IPA mode); and the 2D mode. The differences in domain–averaged normalized radiances of reflection and transmission are insignificant between the 1D or IPA and 2D calculation modes. However, local differences were observed since extinction is hinge on horizontal spatial variability. In the areas with large spatial variability in optical thickness, the radiance fields of the 2D mode differ about ±20% for the first and second Stokes elements (I, Q) from the fields of the 1D mode. This work points to a brand–new field: the quantification of the sensitivity of polarization to 3D radiative effects.

L'avènement d'une nouvelle génération de lasers ultra-relativistes (d'éclairement supérieur à 10^22 W/cm2), tels le laser APOLLON sur le plateau de Saclay, donnera lieu à un régime d'interaction laser-matière sans précédent, couplant physique des plasmas relativistes et effets électrodynamiques quantiques. Sources de particules et de rayonnements aux propriétés énergétiques et spatio-temporelles inédites, ces lasers serviront, entre autres applications, à la mise au point de nouveaux concepts d'accélérateurs et de diagnostics radiographiques, au chauffage de plasmas denses, comme à la reproduction de configurations astrophysiques en laboratoire. En prévision des futures expériences, les codes particle-in-cell (PIC), qui constituent les outils de référence pour la simulation de l'interaction laser-plasma, doivent être enrichis des processus radiatifs et quantiques propres à ce nouveau régime d'interaction. C'est le cas du code CALDER développé au CEA/DAM, qui modélise désormais l'émission de photons énergétiques et la conversion de ceux-ci en paires électron-positron ; autant d'effets susceptibles d'affecter le bilan d'énergie de l'interaction laser-cible et, plus précisément, le rendement du laser en particules et rayonnements énergétiques. L'objet de ce stage théorique est d'étudier, à l'aide du code CALDER, l'influence de ces processus dans un certain nombre de scénarios physiques en champ extrême (accélération électronique et ionique dans un plasma surcritique, production de rayonnement, génération de choc non-collisionnel…). / Forthcoming multi-petawatt laser systems, such as the French Apollon and European Extreme Light Infrastructure facilities, are expected to deliver on-target laser intensities exceeding 10^22 W/cm^2. A novel regime of laser-matter interaction will ensue, where ultra-relativistic plasma effects are coupled with copious generation of high-energy photons and electron-positron pairs. This will pave the way for many transdisciplinary applications in fundamental and applied research, including the development of unprecedentedly intense, compact particle and radiation sources, the experimental investigation of relativistic astrophysical scenarios and tests of quantum electrodynamics theory.In recent years, most theoretical studies performed in this research field have focused on the impact of synchrotron photon emission and Breit-Wheeler pair generation, both directly induced by the laser field and believed to be dominant at intensities >10^22 W/cm^2. At the lower intensities (≲10^21 Wcm^(-2)) currently attainable, by contrast, photon and pair production mainly originate from, respectively, Bremsstrahlung and Bethe-Heitler/Trident processes, all triggered by atomic Coulomb fields. The conditions for a transition between these two regimes have, as yet, hardly been investigated, particularly by means of integrated kinetic numerical simulations. The purpose of this PhD is precisely to study the aforementioned processes under various physical scenarios involving extreme laser-plasma interactions. This work is carried out using the particle-in-cell CALDER code developed at CEA/DAM which, over the past few years, had been enriched with modules describing the synchrotron and Breit-Wheeler processes.Our first study aimed at extending the simulation capabilities of CALDER to the whole range of photon and positron generation mechanisms arising during relativistic laser-plasma interactions. To this purpose, we have implemented modules for the Coulomb-field-mediated Bremsstrahlung, Bethe-Heitler and Trident processes. Refined Bremsstrahlung and Bethe-Heitler cross sections have been obtained which account for electronic shielding effects in arbitrarily ionized plasmas. Following validation tests of the Monte Carlo numerical method, we have examined the competition between Bremsstrahlung/Bethe-Heitler and Trident pair generations by relativistic electrons propagating through micrometer copper foils. Our self-consistent simulations qualitatively agree with a 0-D theoretical model, yet they show that the deceleration of the fast electrons due to target expansion significantly impacts pair production.We then address the competition between Bremsstrahlung and synchrotron emission from copper foils irradiated at 10^22 Wcm^(-2). We show that the maximum radiation yield (into >10 keV photons) is achieved through synchrotron emission in relativistically transparent targets of a few 10 nm thick. The efficiency of Bremsstrahlung increases with the target thickness, and takes over synchrotron for >2μm thicknesses. The spectral properties of the two radiation processes are analyzed in detail and correlated with the ultrafast target dynamics.Finally, we investigate the potential of nanowire-array targets to enhance the synchrotron yield of a 10^22 Wcm^(-2) femtosecond laser pulse. Several radiation mechanisms are identified depending on the target parameters and as a function of time. A simulation scan allows us to identify the optimal target geometry in terms of nanowire width and interspacing, yielding a ∼10% radiation efficiency. In this configuration, the laser-driven nanowire array rapidly expands to form a quasi-uniform, relativistically transparent plasma. Furthermore, we demonstrate that uniform sub-solid targets can achieve synchrotron yields as high as in nanowire arrays, but that the latter enable a strong emission level to be sustained over a broader range of average plasma density.

Atmosphärisches Aerosol kann den Strahlungstransport signifikant beeinflussen. Mineralstaub, der über der Sahara und anderen Wüsten in die Atmosphäre gelangt, ist das hinsichtlich der in letzterer dauerhaft verbleibenden Masse bedeutendste Aerosol. Darüber hinaus sind Saharamineralstaubpartikel nichtkugelförmig, und die Wirkungen dieser Partikeleigenschaft auf den Strahlungstransport in der Erdatmosphäre sind bislang nur ungenügend untersucht worden. Es werden die optischen Eigenschaften, Strahlungs- und Erwärmungseffekte von Saharamineralstaub unter Berücksichtigung der Nichtkugelförmigkeit seiner Partikel quantitativ untersucht, wobei der gesamte, im Hinblick auf den Strahlungshaushalt energetisch relevante Spektralbereich zugrunde gelegt wird. Zunächst werden auf Basis in-situ-gemessener Experimentaldaten die atmosphärischen Umgebungsbedingungen, Größenverteilungen, Brechungsindizes, Bodenalbedo und Partikelgestalt festgelegt, die in einem zweiten Schritt in ein Strahlungstransportmodell einfließen. Mit dessen Hilfe wird in umfangreichen numerischen Simulationen des Strahlungstransports in einer realistischen mineralstaubhaltigen Modellatmosphäre im Vergleich zu Messdaten beispielsweise geklärt, welche Partikelform und Größenäquivalenz angenommener sphäroidaler Modellpartikel am meisten realistisch sind. Des Weiteren werden im Zusammenhang mit der Partikelnichtkugelförmigkeit Sensitivitätsstudien zur Beantwortung der Fragen durchgeführt, inwieweit diese das Strahlungsfeld beeinflusst und zu veränderten Strahlungserwärmungswirkungen führt.

This dissertation aims to study the broadband optical properties and radiative effects of dust aerosols and ice clouds. It covers three main topics: the uncertainty of dust optical properties and radiative effects from the dust particle shape and refractive index, the influence of ice particle surface roughening on the global cloud radiative effect, and the simulations of the global contrail radiative forcing. In the first part of this dissertation, the effects of dust non-spherical shape on radiative transfer simulations are investigated. We utilize a spectral database of the single-scattering properties of tri-axial ellipsoidal dust-like aerosols and determined a suitable dust shape model. The radiance and flux differences between the spherical and ellipsoidal models are quantified, and the non-spherical effect on the net flux and heating rate is obtained over the solar spectrum. The results indicate the particle shape effect is related to the dust optical depth and surface albedo. Under certain conditions, the dust particle shape effect contributes to 30% of the net flux at the top of the atmosphere. The second part discusses how the ice surface roughening can exert influence on the global cloud radiative effect. A new broadband parameterization for ice cloud bulk scattering properties is developed using severely roughened ice particles. The effect of ice particle surface roughness is derived through simulations with the Fu-Liou and RRTMG radiative transfer codes and the Community Atmospheric Model. The global averaged net cloud radiative effect due to surface roughness is around 1.46 Wm-2. Non-negligible increase in longwave cloud radiative effect is also found. The third part is about the simulation of global contrail radiative forcing and its sensitivity studies using both offline and online modeling frameworks. Global contrail distributions from the literature and Contrail Cirrus Prediction Tool are used. The 2006 global annual averaged contrail net radiative forcing from the offline model is estimated to be 11.3 mW m^(-2), with the regional contrail radiative forcing being more than ten times stronger. Sensitivity tests show that contrail effective size, contrail layer height, the model cloud overlap assumption, and contrail optical properties are among the most important factors.

In this thesis a new three–dimensional (3D) vector radiative transfer model, the Solver for Polarized Atmospheric Radiative Transfer Applications (SPARTA) is introduced, validated against benchmark results, and applied to scientific problems. SPARTA employs the statistical forward Monte Carlo technique for efficient column–response pixel–based radiance calculations comprising polarization for 3D inhomogeneous cloudless and cloudy atmospheres. By means of SPARTA, two scientific issues in the field of radiative transfer are investigated. A sensitivity study has been conducted to illustrate the errors introduced by neglecting the effects of polarization in radiation simulations. Two atmospheric scenarios have been considered: a pure one–dimensional (1D) Rayleigh atmosphere and two–dimensional (2D) realistic inhomogeneous dust fields. In case of a purely molecular atmosphere, these errors strongly depend on molecular anisotropy, isotropic reflection, and more importantly, on single scattering albedo and optical thickness (saturation occurs for τ close to 1). Overall errors in the reflected field range up to about 10.5%. On the other hand, for rather high optical thickness, the bias induced by ignoring polarization for realistic inhomogeneous atmospheres is negligible (less than 1%). In addition, solar radiative transfer simulations for LIDAR–measured fields of optical properties of Saharan dust have been performed in order to quantify the effects induced by neglecting the horizontal photon transport and internal inhomogeneities (3D radiative effects) in radiance simulations including polarization. Results are presented for two exemplary mineral dust fields constructed from LIDAR observations. For each case, three radiative calculations are investigated: a 1D calculation according to the plane–parallel (1D mode); an Independent Pixel Approximation (IPA mode); and the 2D mode. The differences in domain–averaged normalized radiances of reflection and transmission are insignificant between the 1D or IPA and 2D calculation modes. However, local differences were observed since extinction is hinge on horizontal spatial variability. In the areas with large spatial variability in optical thickness, the radiance fields of the 2D mode differ about ±20% for the first and second Stokes elements (I, Q) from the fields of the 1D mode. This work points to a brand–new field: the quantification of the sensitivity of polarization to 3D radiative effects.

Atmosphärisches Aerosol kann den Strahlungstransport signifikant beeinflussen. Mineralstaub, der über der Sahara und anderen Wüsten in die Atmosphäre gelangt, ist das hinsichtlich der in letzterer dauerhaft verbleibenden Masse bedeutendste Aerosol. Darüber hinaus sind Saharamineralstaubpartikel nichtkugelförmig, und die Wirkungen dieser Partikeleigenschaft auf den Strahlungstransport in der Erdatmosphäre sind bislang nur ungenügend untersucht worden. Es werden die optischen Eigenschaften, Strahlungs- und Erwärmungseffekte von Saharamineralstaub unter Berücksichtigung der Nichtkugelförmigkeit seiner Partikel quantitativ untersucht, wobei der gesamte, im Hinblick auf den Strahlungshaushalt energetisch relevante Spektralbereich zugrunde gelegt wird. Zunächst werden auf Basis in-situ-gemessener Experimentaldaten die atmosphärischen Umgebungsbedingungen, Größenverteilungen, Brechungsindizes, Bodenalbedo und Partikelgestalt festgelegt, die in einem zweiten Schritt in ein Strahlungstransportmodell einfließen. Mit dessen Hilfe wird in umfangreichen numerischen Simulationen des Strahlungstransports in einer realistischen mineralstaubhaltigen Modellatmosphäre im Vergleich zu Messdaten beispielsweise geklärt, welche Partikelform und Größenäquivalenz angenommener sphäroidaler Modellpartikel am meisten realistisch sind. Des Weiteren werden im Zusammenhang mit der Partikelnichtkugelförmigkeit Sensitivitätsstudien zur Beantwortung der Fragen durchgeführt, inwieweit diese das Strahlungsfeld beeinflusst und zu veränderten Strahlungserwärmungswirkungen führt.

This thesis is based on measurements of aerosol optical and microphysical properties made at inland, coastal and island locations in India. Aerosol vertical distribution measurements have also been made both using surface based and aircraft borne instruments. In addition to these, satellite based measurements (MODIS and OMI) have also been used to estimate regional aerosol radiative forcing over the oceanic regions around India. The measurements at an inland, continental, urban location reveals the large effect of anthropogenic activities on aerosol characteristics at surface and the atmospheric vertical column. A clear seasonality is observed in aerosol optical and microphysical properties as a consequence of modulation by anthropogenic activities and the effect of meteorological parameters like rainfall, winds and boundary layer dynamics. The variability observed at different time scales (from diurnal, weekly, monthly to annual) reveals the importance of anthropogenic and natural processes in modulating the aerosol loading. The estimates of aerosol radiative forcing at surface were as high as ~ 40W m-2. A large discrepancy was observed between the observed and modeled aerosol forcing efficiency (forcing per unit optical depth) at surface. These discrepancies are due to the inadequate representation of aerosol mixing state in models. In addition, the large difference found in the observed forcing between winter and summer could also be influenced due to the presence of elevated aerosols during the summer. Measurements made over coastal and central India shows that a large fraction (75-85%) of aerosol column optical depth was contributed by aerosols located above 1 km. The horizontal gradients were sharp with e-1 scaling distance as small as ~250 km in the well-mixed regions mostly under the influence of local source effects. However, above the atmospheric boundary layer, the gradients were much shallower (~800 to 1200 km). In addition, a large fraction (60-75%) of aerosol was found located above clouds leading to enhanced aerosol absorption. Large spatial gradient in aerosol optical depth and hence radiative impacts between the coastal landmass and the adjacent oceans within a short distance of <300 km (even at an altitude of 3 km) during summer and pre-monsoon is of importance to regional climate. Observations at Minicoy, a remote island in southern Arabian Sea to study the characteristics of transported aerosols reveals variability at daily, weekly, monthly and seasonal time scales associated with changes in precipitation and air mass characteristics. The daily mean Black Carbon (BC) mass mixing ratio varied between as low as ~ 0.2 to 9.0%. The resultant average aerosol atmospheric forcing for the observation period was ~15 W m-2. Trajectory based cluster analysis has shown six distinct advection/transport pathways influencing aerosol characteristics over southern Arabian Sea. The Indo-Gangetic Plain, northern Arabian Sea and west Asia are identified to be the most important source regions having a major impact on aerosols loading over the southern Arabian Sea. The cluster analysis, concentration weighted trajectory (CWT) analysis and the MODIS retrievals show an asymmetry in aerosol characteristics between the Arabian Sea and the Bay of Bengal, with the Arabian Sea characterized by large loading by natural aerosols (eg., dust and sea salt) and the Bay of Bengal characterized by anthropogenic loading (eg., BC). The low value of the BC mass mixing ratio measured at the island (mostly ~ 1 to 1.6%), has major implications for regional radiative forcing. The annually averaged net aerosol atmospheric forcing was as low as ~1.7 W m-2 with highest forcing corresponding to IGP cluster. The single scattering albedo (SSA) which is an important parameter in the estimation of aerosol radiative forcing was retrieved by utilizing a joint OMI-MODIS retrieval methodology. The SSA over the oceanic regions around India shows that the largest absorption (SSA < 0.9) occurs during winter. The largest gradients in AOD and SSA were observed over Arabian Sea during the summer as a result of large dust emissions. The largest forcing observed also was confined to the northern Arabian Sea (~ 37 W m-2) as a result of high aerosol column loading and dust transport. The observed annual mean forcing at Minicoy were comparable to that estimated using satellite measurements, but were much lower than those observed during INDOEX.

Title: Coupling atmospheric chemistry/aerosols to regional climate models Author: Peter Huszár Department: Department of Meteorology and Environment Protection Supervisor: doc. RNDr. Tomáš Halenka, CSc. Supervisor's e-mail address: tomas.halenka@mff.cuni.cz Abstract: In this thesis, the connections between air quality and climate are studied. For this purpose, regional climate model RegCM3 and chemistry transport model CAMx has been coupled offline with one- and two-way interaction. Our work represents a first attempt to connect RegCM3 not only with CAMx, but with any other chemistry transport model. As a first step, an offline one way couple of RegCM3 and CAMx has been developed, meaning that the climate model drives the transport, emission, chemical transformation and deposition of species while the radiative feedbacks of gases and aerosols are not considered. A meteorological interface has been developed at our department in order to convert the meteorological data generated by RegCM3 to fields required by CAMx. For those parameters that are essential for CAMx but the regional climate model does not supply them, diagnostic methods were implemented into this interface. Further, it is used to calculate biogenic emissions. Regarding anthropogenic emissions, a simple utility has been developed to...

In dieser Arbeit untersuchen wir kollektive Strahlungseffekte in Nanofaser-gekoppelten atomaren Ensembles, die sich über Tausende von optischen Wellenlängen erstrecken. Wir koppeln bis zu 1000 Atome optisch an die geführten Moden einer optischen Nanofaser, die langreichweitige Dipol-Dipol Wechselwirkungen zwischen den Atomen vermittelt. Wir realisieren eine unidirektionale Kopplung und damit ein kaskadiertes Quantensystem, in dem die Dynamik jedes Atoms ausschließlich durch die Dynamik der vorgelagerten Atome bestimmt wird. Wir regen die Atome mit nanofasergeführten optischen Pulsen kohärent an, was uns ermöglicht, den gesamten Parameterbereich von schwacher Anregung bis hin zur voll-ständigen Inversion zu erforschen. Wir stellen fest, dass die kohärente Vorwärtsstreuung, die für die Superradianz im Regime der schwachen Anregung verantwortlich ist, auch nahe voller Inversion eine wichtige Rolle für die Dynamik spielt. Wir beobachten superradiante Puls-Dynamik, die in unserem System trotz des makroskopischen Abstands zwischen den Atomen und einer asymmetrischen Kopplung auftritt. Wir stellen fest, dass die emittierte Spitzenleistung noch schneller mit der Anzahl der Atome skaliert als im Fall der idealen Dicke Superradianz, was auf eine kollektiv erhöhte Sammeleffizienz der nanofasergeführten Mode zurückzuführen ist. Die Analyse der Kohärenz-Eigenschaften des superradianten Pulses erlaubt es uns, zwei Regime der Puls-Dynamik zu identifizieren. Wir entwickeln ein kaskadiertes Wechselwirkungsmodell und zeigen, dass es die kollektive Dynamik unseres Systems über den gesamten in dieser Arbeit untersuchten Parameterbereich akkurat beschreibt. Schließlich untersuchen wir die getriebene Dynamik eines Nanofaser-gekoppelten Ensembles von Drei-Niveau-Atomen. Wir treiben Zwei-Photonen-Rabi-Oszillationen zwischen den beiden Grundzuständen eines $\Lambda$-Systems und beobachten die damit verbundene oszillatorische Raman-Verstärkung und -Absorption. / In this thesis, we study collective radiative effects in nanofiber-coupled atomic ensembles that extend over thousands of optical wavelengths. We optically couple up to 1000 atoms to the guided modes of an optical nanofiber, which mediates long-range dipole-dipole interactions between the atoms. We engineer the coupling to be unidirectional, realizing a cascaded quantum system in which the dynamics of each atom is solely determined by the dynamics of upstream atoms. We coherently excite the atoms using nanofiber-guided optical pulses, allowing us to explore the entire parameter regime from weak excitation to full inversion. We find that coherent forward scattering, which is responsible for superradiance in the weak excitation regime, plays an important role for the dynamics even close to full inversion. We observe superradiant burst dynamics, which occurs in our system despite the macroscopic separation between the atoms and an asymmetric coupling. We find that the peak-emitted power scales even faster with the number of atoms than in the case of ideal Dicke superradiance due to a collectively enhanced channeling efficiency into the nanofiber-guided mode. By analyzing the coherence properties of the superradiant burst, we directly identify two regimes of burst dynamics. In the second regime, there is no initial coherence, and the superradiant burst is seeded by vacuum fluctuations. We introduce a cascaded interaction model and find that it accurately describes the collective dynamics of our system over the entire parameter regime explored in this thesis. Finally, we study the driven dynamics of a nanofiber-coupled ensemble of three-level atoms. We drive two-photon Rabi oscillations between the two ground states of a $\Lambda$ system and observe the associated oscillatory Raman gain and absorption.