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Three aspects of the Habitability of the Northern Plains of Mars to organics and terrestrial-like microbial life were assessed. (1) Protection offered by small surface features and (2) the breakdown of rocks to form soils were examined using a radiative transfer computer model. Two separate sublimation experiments provided a basis to improve (3) estimates of the amount of available water today and in the past by determining the fractionation of HDO between present-day reservoirs.(1) UV radiation sterilizes the hardiest of terrestrial organisms within minutes on the Martian surface. Small surface features including pits, trenches, flat faces and overhangs may create "safe havens" for organisms by blocking much of the UV flux. In the most favorable cases, this flux is sufficiently reduced such that organic in-fall could accumulate beneath overhanging surfaces and in pits and cracks while terrestrial microorganisms could persist for several tens of martian years.(2) The production of soils on the surface is considered by analogy with the arid US Southwest. Here differential insolation of incipient cracks of random orientations predicts crack orientation distributions consistent with field observations by assuming that only crack orientations which shield their interiors, minimizing their water loss, can grow, eventually disrupting the clast.(3) Disaggregated water ice to simulate the polar caps was produced by flash freezing in liquid nitrogen and crushing. When dust was added to the mixtures, the D/H ratio of the sublimate gas was seen to decrease with time from the bulk ratio. The more dust was added to the mixture, the more pronounced was this effect. The largest fractionation factor observed during these experiments was 2.5. Clean ice was also prepared and overlain by dust to simulate ground ice. Here, the movement of water vapor was modeled using an effective diffusivity that incorporated both adsorption on grains and diffusion. For low temperatures (<-55°C) a significant difference between the diffusivities of H2O and HDO was observed. This suggests adsorptive-control within the regolith as energies of interaction are 60-70kJmol-1. This ability of the martian regolith to preferentially adsorb HDO decouples the ice table and polar caps from the atmosphere and allows for geographic variations in the D/H ratio on Mars.

Land surface albedo plays a key role in the surface-atmosphere internaction, because it greatly influences the shortwave radiation absorbed by the surface. Surface albedo depends on soil characteristics and vegetation types. Error in the specification of albedos of soil and vegetation may cause biases in the computation of ground temperature and surface fluxes, therefore accurate albedo estimates are essential for an accurate simulation of the Earth's climate. The study demonstrates the importance of MODIS data in assessing and improving albedo parameterization in weather forecast and climate models as well as the remote sensing retrieval of surface solar fluxes through a series of three papers. First, the NCAR Community Climate System Model (CCSM2) albedo is evaluated using the MODIS BRDF and albedo data. The model and MODIS albedo differences are related to the deficiences in the model simulation of snow cover and soil moisture and in the model's specification of leaf and stem area indexes. They are also partially caused by the deficiency of the two-stream method. Second, motivated by these analyses, a new formulation for surface albedo is developed. Over desert, most land models assume that the bare soil albedo is a function of soil color and soil moisture but independent of solar zenith angle (SZA). However, analysis of MODIS BRDF/albedo data and in situ data indicates that bare soil albedo does vary with SZA. Furthermore this SZA dependence is found to affect the surface energy fluxes and temperature in the offline land surface model sensitivity tests. Finally, the MODIS BRDF algorithm is reformulated to derive a new two-parameter scheme for the computation of land surface albedo and its SZA dependence for use in weather and climate models as well as the remote sensing retrieval of surface solar fluxes. In this formulation, the season- and pixel-dependent black-sky albedo at 60 deg SZA can be directly prescribed using the MODIS BRDF data while the two parameters are taken as a function of vegetation type only. Comparison of this formulation with those used in weather, climate, and data assimilation models (at NCAR, NCEP, and NASA) as well as those used in remote sensing groups (University of Maryland, ISCCP-FD, and CERES/TRMM) reveals the deficiencies in the land surface albedo treatment in these models and remote sensing retrieval algorithm along with suggestions for improvement.

The radiative mechanism responsible for the prompt gamma-ray burst (GRB) emission remains elusive. For the last decade, optically thin synchrotron emission from shocks internal to the GRB jet appeared to be the most plausible explanation. However, the synchrotron interpretation is incompatible with a significant fraction of GRB observations, highlighting the need for new ideas. In this thesis, it is shown that the narrow, dominating component of the prompt emission from the bright GRB090902B is initially consistent only with emission released at the optically thick jet photosphere. However, this emission component then broadens in time into a more typical GRB spectrum, which calls for an explanation. In this thesis, a previously unconsidered way of broadening the spectrum of photospheric emission, based on considerations of the lateral jet structure, is presented and explored. Expressions for the spectral features, as well as polarization properties, of the photospheric emission observed from structured, relativistic jets are derived analytically under simplifying assumptions on the radiative transfer close to the photosphere. The full, polarized radiative transfer is solved through Monte Carlo simulations, using a code which has been constructed for this unique purpose. It is shown that the typical observed GRB spectrum can be obtained from the photosphere, without the need for additional, commonly assumed, physical processes (e.g. energy dissipation, particle acceleration, or additional radiative processes). Furthermore, contrary to common expectations, it is found that the observed photospheric emission can be highly linearly polarized (up to $\sim 40 \, \%$). In particular, it is shown that a shift of $\pi/2$ of the angle of polarization is the only shift allowed by the proposed model, consistent with the only measurement preformed to date. A number of ways to test the theory is proposed, mainly involving simultaneous spectral and polarization measurements. The simplest measurement, which tests not only the proposed theory but also common assumptions on the jet structure, involves only two consecutive measurements of the angle of polarization during the prompt emission. / <p>QC 20131204</p>

The maximum entropy moment closure for the two-moment approximation of the radiative transfer equation is presented. The resulting moment equations, known as the M1 model, are solved using a finite-volume method with adaptive mesh refinement (AMR) and two Riemann-solver based flux function solvers: a Roe-type and a Harten-Lax van Leer (HLL) solver. Three different boundary schemes are also presented and discussed. When compared to the discrete ordinates method (DOM) in several representative one- and two-dimensional radiation transport problems, the results indicate that while the M1 model cannot accurately resolve multi-directional radiation transport occurring in low-absorption media, it does provide reasonably accurate solutions, both qualitatively and quantitatively, when compared to the DOM predictions in most of the test cases involving either absorbing-emitting or scattering media. The results also show that the M1 model is computationally less expensive than DOM for more realistic radiation transport problems involving scattering and complex geometries.

The maximum entropy moment closure for the two-moment approximation of the radiative transfer equation is presented. The resulting moment equations, known as the M1 model, are solved using a finite-volume method with adaptive mesh refinement (AMR) and two Riemann-solver based flux function solvers: a Roe-type and a Harten-Lax van Leer (HLL) solver. Three different boundary schemes are also presented and discussed. When compared to the discrete ordinates method (DOM) in several representative one- and two-dimensional radiation transport problems, the results indicate that while the M1 model cannot accurately resolve multi-directional radiation transport occurring in low-absorption media, it does provide reasonably accurate solutions, both qualitatively and quantitatively, when compared to the DOM predictions in most of the test cases involving either absorbing-emitting or scattering media. The results also show that the M1 model is computationally less expensive than DOM for more realistic radiation transport problems involving scattering and complex geometries.

A change in the atmospheric inventory of a greenhouse gas produces a radiative forcing on the atmosphere which results in climatic change. Thus to understand climate change resulting from perturbations to atmospheric greenhouse gas concentrations it is necessary to quantify the radiative forcing. Here, radiative forcings are presented for large changes in atmospheric CO2, CH4, and N2O in the modern atmosphere and large changes in atmospheric CO2, CH4 and 18 other gases for the Archean atmosphere. For the modern Earth, I present new calculations of radiative forcing at very high concentrations of CO2, CH4, and N2O, relevant to extreme anthropogenic climate change and paleoclimate studies. CO2 forcing is calculated over the range 100 ppmv to 50,000 ppmv. CH4, and N2O forcings are calculated over the range 100 ppbv to 100 ppmv. The sensitivity of these calculations to spatial averaging and tropopause definition are examined. I compare our results with the ``simplified expressions'' reported by IPCC, and find significant differences at high greenhouse gas concentrations. I provide new simplified expressions which agree much better with the calculated forcings, and suggest that these expressions be used in place of the IPCC expressions. Additionally, I provide meridionally resolved forcings which may be used to force simple and intermediate complexity climate models. For the Archean Earth, I present new calculations of radiative forcing for CO2 (10^-6 - 1 bar), CH4 (500 ppbv - 10,000 ppmv) and 18 other gases (10 ppbv - 10 ppmv). I aim to provide a set of radiative forcing and overlap calculations which can be used as a standard for comparisons. Radiative forcings are calculated for atmospheres with various N2 inventories (0.5, 1, and 2 bar). The effect of overlap and atmospheric pressure on radiative forcing are examined. The CO2 radiative forcings are consistent with previous work, however, I find significantly more shortwave absorption by CH4 than previously reported which may limit warming above 100 ppmv. For the 18 other gases, I find that significant radiative forcings result from low concentrations (<1 ppmv). These forcings are compared to those given in the literature. / Graduate / 0756 / 0608 / 0725 / bbyrne@uvic.ca

A change in the atmospheric inventory of a greenhouse gas produces a radiative forcing on the atmosphere which results in climatic change. Thus to understand climate change resulting from perturbations to atmospheric greenhouse gas concentrations it is necessary to quantify the radiative forcing. Here, radiative forcings are presented for large changes in atmospheric CO2, CH4, and N2O in the modern atmosphere and large changes in atmospheric CO2, CH4 and 18 other gases for the Archean atmosphere. For the modern Earth, I present new calculations of radiative forcing at very high concentrations of CO2, CH4, and N2O, relevant to extreme anthropogenic climate change and paleoclimate studies. CO2 forcing is calculated over the range 100 ppmv to 50,000 ppmv. CH4, and N2O forcings are calculated over the range 100 ppbv to 100 ppmv. The sensitivity of these calculations to spatial averaging and tropopause definition are examined. I compare our results with the ``simplified expressions'' reported by IPCC, and find significant differences at high greenhouse gas concentrations. I provide new simplified expressions which agree much better with the calculated forcings, and suggest that these expressions be used in place of the IPCC expressions. Additionally, I provide meridionally resolved forcings which may be used to force simple and intermediate complexity climate models. For the Archean Earth, I present new calculations of radiative forcing for CO2 (10^-6 - 1 bar), CH4 (500 ppbv - 10,000 ppmv) and 18 other gases (10 ppbv - 10 ppmv). I aim to provide a set of radiative forcing and overlap calculations which can be used as a standard for comparisons. Radiative forcings are calculated for atmospheres with various N2 inventories (0.5, 1, and 2 bar). The effect of overlap and atmospheric pressure on radiative forcing are examined. The CO2 radiative forcings are consistent with previous work, however, I find significantly more shortwave absorption by CH4 than previously reported which may limit warming above 100 ppmv. For the 18 other gases, I find that significant radiative forcings result from low concentrations (<1 ppmv). These forcings are compared to those given in the literature. / Graduate / 0756 / 0608 / 0725 / bbyrne@uvic.ca

A complete renormalization scheme for the Glashow-Salam-Weinberg model is presented. As input parameters the scheme uses the fine structure constant, α, the muon decay constant, G_μ and the Z° mass, M_Z which are known or will be measured to high accuracy in the near future. These are used along with the Higgs and fermion masses to obtain the W mass, M_W. The full one-loop weak radiative corrections to the longitudinal polarization asymmetry, A_pol, and the forward-backward asymmetry, A_fb, in e⁺e^- → μ⁺μ^- are then calculated both on and off resonance. On resonance the results depend extremely sensitively on the Z mass, M_Z, and to a lesser extent on the top quark mass, m_t, and the Higgs mass, M_H, showing that this is a good place to test the standard model at the one loop level. The results are displayed over the full range of the parameters allowed by experimental and theoretical constraints. It is suggested that sufficiently accurate experiments may be able to set an upper bound on one of m_t or M_H if the other is known. It is noted that on resonance A_pol is only weakly dependent on the beam pipe and on the nature of the outgoing fermions. Comparison is made with other calculations of A_fb and the agreement is found to be good. The predictions are also compared with measurements of A_fb off resonance and are found in all cases to lie within the experimental errors. Previous analyses that indicated a possible discrepancy are shown to be incorrect.

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