The predictions of non-equilibrium radiation for a Titan aerocapture aeroshell vary significantly amongst Computational Fluid Dynamics (CFD) analyses and are limited by the physical models of the non-equilibrium flow. Of particular interest are the non-equilibrium processes associated with the cyanogen (CN) molecule which is known to be a strong radiator. It is therefore important to have experimental data for these radiating shock layers which will allow for validation of CFD models. Furthermore, a more detailed understanding of the chemical processes that lead to the formation of CN above equilibrium concentration is required. This thesis describes the modelling of the radiation behind a shock using a collisional-radiative (CR) model and presents measurements of radiation intensity behind a shock in simulated Titan and Martian atmospheres. The uncertainties in radiation is more significant at lower speeds (around 5-8 km/s) with these atmospheres when compared to Earth entry. This is due to the formation of CN and because of the highly non-equilibrium nature of the flow. The motivation for this work began with the successful landing of the Huygens probe on the surface of Titan which led to the renewed interest in inter-planetary missions. Thus radiative heating during atmospheric entry to Titan and Mars was the subject of several experimental campaigns and extensive computational analyses. In order to better understand the formation of CN, and the nonequilibrium radiation emitted under such atmospheric conditions, NASA Ames Research Center conducted a series of experiments on their Electric Arc Shock Tube facility, EAST. Furthermore, several research groups in Europe and the United States independently developed CR models to predict the measured levels of radiation. The results from these simulations showed some ma jor discrepancies and highlighted a lack of knowledge and understanding about the fundamental physics behind the formation and decay of the CN molecule and its associated excited states. Based on a comparison of the various simulations with the CR models and the EAST experimental data, it was concluded that the absolute level of peak radiation was well predicted, however, there was a significant discrepancy related to the decay rate of the radiation. Therefore, to add to the relatively small amount of experimental data for these highly non-equilibrium radiating flow conditions, experiments were performed on the X2 shock tube at The University of Queensland with the aim of producing a comprehensive set of benchmark data for Titan entry. The data obtained from these experiments have been used to validate the results from the NASA Ames testing, and due to the large parametric variation, as a source for code validation. In addition to the experimental component of this thesis, an investigation into the simulation of CN non-equilibrium radiation was conducted. It has been previously concluded that there was a significant discrepancy between the experimentally measured radiation decay rate and the predicted value from CR models. Therefore, the primary aim of the simulation work presented in this thesis is to explain the reason behind this discrepancy. Through a parametric study of important reactions combined with an analysis of the reaction set, it was concluded that the coupling between the dissociation of N2 and the formation of CN (through the reaction N2 + C ↔ CN + N) controlled the radiation decay rate. The reason for the super equilibrium concentrations was identified to be a result of the N2 + C ↔ CN + N reaction continuing to over-produce CN after nominal equilibrium values are reached. This is due to the slow build up of N to drive the reverse reaction. Thus it has been shown in this thesis that the behaviour of the CN concentration is controlled by the rate of N2 dissociation. This led to the implementation of a more thorough method for simulating the dissociation process of molecular nitrogen. Therefore, a mono-quantum vibration state specific model that includes excitation and de-excitation reactions for all the vibrational states of nitrogen was incorporated into the CR model developed by Magin et al. The nitrogen vibration state specific model that was implemented was developed by Pierott and is based on SSH theory. The model developed in this thesis is known as the ViSpeN CR model (Vibrationally Specific Nitrogen). The ViSpeN results show significantly better agreement with experimental data in terms of the decay rate, initial rise of the radiation and the overall trends in the data. However, the work in this thesis has shown there are still discrepancies in predicting the absolute level of radiation measured in shock tunnel experiments. This led to the development of a modification to the ViSpeN model (known as ViSpeN-L) which includes a proposed new value for the radiative lifetime of the CN violet transition. The agreement between the experimental data and the ViSpeN-L model is excellent for conditions relevant to Titan entry.

Thesis (Ph. D.)--University of Washington, 1989. / Vita. Includes bibliographical references (leaves [118]-122).

Thesis (Ph.D.(Metallurgical Engineering))--University of Pretoria, 2007. / Summaries in Afrikaans and English. Includes bibliographical references.

Mémoire (M.Sc.A.)--Université du Québec à Chicoutimi, 1991. / Document électronique également accessible en format PDF. CaQCU

Thesis (M.S.)--Florida State University, 2004. / Advisor: Dr. Xiaolei Zou, Florida State University, College of Arts and Sciences, Dept. of Meteorology. Title and description from dissertation home page (viewed Jan. 12, 2005). Includes bibliographical references.

Thesis (Ph. D.)--University of Chicago, Dept. of Physics. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Chicago, Department of Physics, March 2003. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph.D.)--Ohio University, November, 2006. / Title from PDF t.p. Includes bibliographical references.

xv, 165 p. A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / The amount of solar radiation at the earth's surface is modulated by fluctuations in aerosol density and cloud optical depth--two uncertain factors in climate change studies. The University of Oregon Solar Radiation Monitoring Lab has collected five-minute resolution surface shortwave irradiance measurements at three sites in Oregon since 1980 or earlier. Direct normal surface solar irradiance has increased 4-5% per decade (8-11 W/m 2 per decade) at these three sites since 1980 (1979 in Eugene). Total solar irradiance has likewise increased by 1-2% per decade (2-3 W/m 2 per decade). This unusually long direct normal time series was used to examine the causes of trends because of its high sensitivity to scattering and high instrumental accuracy. The strongest factor causing direct normal irradiance trends was found to be the high stratospheric aerosol concentrations after the volcanic eruptions of El Chichà à à à ³n (1982) and Mt. Pinatubo (1991). Removing the four years most impacted by each volcanic eruption (1982-1985 and 1991-1994) reduces the trend in annual average direct normal irradiance by 20-55%, depending on the site. All measurement sites show low irradiance values before the volcanic eruption of El Chichà à à à ³n in 1982 compared to later periods of relatively low volcanic aerosols (1989- 1990, and 2000-2007). These low values are visible both in all-sky and clear-sky monthly averages, suggesting high aerosol loads as a likely cause. Clear-sky direct normal irradiance measurements from high solar zenith angles (6575à à à à °) are analyzed to test the hypothesis that the increase in irradiance comes from a reduction of anthropogenic aerosols since the late 1980s. No change in anthropogenic aerosols between 1987 and 2007 is detectable within the noise of the data. Even after removing the four years most heavily impacted by volcanic eruptions, the continued reduction of volcanic aerosol loads causes over half of the clear-sky direct normal irradiance increase since 1987. The remaining increase could be accounted for by a 20-year decrease in 550 nm aerosol optical depth of .005 à à à à ± .005, or 6% à à à à ± 6%, but considerable statistical uncertainty exists. / Adviser: Gregory Bothun

En atmosphère naturelle, l’eau est l’un des facteurs contribuant fortement à la masse des particules d’aérosol. Ceci va fortement modifier les propriétés optiques et radiatives des aérosols. Cet impact a été calculé à partir de plus de 2 ans de mesures sur le site ACTRIS/GAW du Puy de Dôme (PdD, 1565m). La distribution en taille, l’extinction et l’hygroscopicité mesurées au PdD ont été combinées pour calculer les propriétés optiques et radiatives, sèches ou humides. Pour chaque propriété, le facteur d’accroissement hygroscopique (f) a été estimé à l’aide d’un code de Mie. La longue série temporelle a permis de paramétrer l’évolution en fonction de l’humidité des propriétés optiques de différents types d’aérosols. Pour un aérosol d’origine océanique qui s’est mélangé avec des aérosols anthropiques, le coefficient de diffusion augmente plus de 4.4 fois si il est placé à 90% d’humidité. Le forçage radiatif va évoluer en conséquence et sera 2.8 fois plus élevé à 90% d’humidité que pour une atmosphère sèche (1.8 à humidité ambiante). Cette longue série de mesures a également permis de montrer, pour la première fois à notre connaissance, la forte variation saisonnière de ce paramètre. Ce manuscrit présente également une méthode originale pour calculer la masse d’aérosols volcaniques à partir de mesures LIDAR et in situ. Lors de l’éruption du volcan Islandais Eyjafjalla en Mai 2010, la masse d’aérosols volcaniques au dessus de Clermont a été estimée de 655±23μg.m-3. / Water contributes significantly to the aerosol mass under ambient conditions of relative humidities, and thus may significantly impact their optical and radiative properties and direct effect. In the present work, the impact of the aerosol hygroscopicity on its optical properties is evaluated from a set of instrumentation located at the ACTRIS/GAW Puy de Dôme station (PdD, 1465m) over two years of measurements in 2010 and 2011. In situ size distributions, extinction and hygroscopicity measurements are combined to retrieve the aerosol refractive index, both dry and wet. For each optical property the enhancement factor (f) due to hygroscopicity can be computed using Mie calculations. The long data set available enables us to generate parameterisations of optical properties enhancement as a function of relative humidities for different aerosol types. At 90% humidity, fσsca is more than 4.4 for marine aerosol that have mixed with a pollution plume. Consequently, the aerosol radiative forcing is estimated to be 2.80 times higher at RH=90% and 1.75 times higher at ambient RH when hygroscopic growth of the aerosol is considered. For the first time this study highlight the high seasonal variability of this impact. The manuscript also presents an original method of mass inversion for volcanic aerosols with the synergy of in situ and LIDAR measurements. The calculated mass of volcanic particle transported over Clermont during the eruption of Eyjafjalla in May 2010 was up to 655±23μg.m-3.