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Evaluating long-term changes and their causes in surface solar irradiance in OregonRiihimaki, Laura, 1979- 09 1900 (has links)
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
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Variability in GRMHD Simulations of Sgr A*: Implications for EHT Closure Phase ObservationsMedeiros, Lia, Chan, Chi-kwan, Özel, Feryal, Psaltis, Dimitrios, Kim, Junhan, Marrone, Daniel P., Sa̧dowski, Aleksander 19 July 2017 (has links)
Closure phases along different baseline triangles carry a large amount of information regarding the structures of the images of black holes in interferometric observations with the Event Horizon Telescope. We use long time span, high cadence, GRMHD+radiative transfer models of Sgr A* to investigate the expected variability of closure phases in such observations. We find that, in general, closure phases along small baseline triangles show little variability, except in the cases when one of the triangle vertices crosses one of the small regions of low visibility amplitude. The closure phase variability increases with the size of the baseline triangle, as larger baselines probe the small-scale structures of the images, which are highly variable. On average, the funnel-dominated MAD models show less closure phase variability than the disk-dominated SANE models, even in the large baseline triangles, because the images from the latter are more sensitive to the turbulence in the accretion flow. Our results suggest that image reconstruction techniques need to explicitly take into account the closure phase variability, especially if the quality and quantity of data allow for a detailed characterization of the nature of variability. This also implies that, if image reconstruction techniques that rely on the assumption of a static image are utilized, regions of the u-v space that show a high level of variability will need to be identified and excised.
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The Circumstellar Disk HD 169142: Gas, Dust, and Planets Acting in Concert?Pohl, A., Benisty, M., Pinilla, P., Ginski, C., Boer, J. de, Avenhaus, H., Henning, Th., Zurlo, A., Boccaletti, A., Augereau, J.-C., Birnstiel, T., Dominik, C., Facchini, S., Fedele, D., Janson, M., Keppler, M., Kral, Q., Langlois, M., Ligi, R., Maire, A.-L., Ménard, F., Meyer, M., Pinte, C., Quanz, S. P., Sauvage, J.-F., Sezestre, É., Stolker, T., Szulágyi, J., Boekel, R. van, Plas, G. van der, Villenave, M., Baruffolo, A., Baudoz, P., Mignant, D. Le, Maurel, D., Ramos, J., Weber, L. 16 November 2017 (has links)
HD 169142 is an excellent target for investigating signs of planet-disk interaction due to previous evidence of gap structures. We perform J-band (similar to 1.2 mu m) polarized intensity imaging of HD 169142 with VLT/SPHERE. We observe polarized scattered light down to 0 ''.16 (similar to 19 au) and find an inner gap with a significantly reduced scattered-light flux. We confirm the previously detected double-ring structure peaking at 0 ''.18 (similar to 21 au) and 0 ''.56 (similar to 66 au) and marginally detect a faint third gap at 0 ''.70-0 ''.73 (similar to 82-85 au). We explore dust evolution models in a disk perturbed by two giant planets, as well as models with a parameterized dust size distribution. The dust evolution model is able to reproduce the ring locations and gap widths in polarized intensity but fails to reproduce their depths. However, it gives a good match with the ALMA dust continuum image at 1.3 mm. Models with a parameterized dust size distribution better reproduce the gap depth in scattered light, suggesting that dust filtration at the outer edges of the gaps is less effective. The pileup of millimeter grains in a dust trap and the continuous distribution of small grains throughout the gap likely require more efficient dust fragmentation and dust diffusion in the dust trap. Alternatively, turbulence or charging effects might lead to a reservoir of small grains at the surface layer that is not affected by the dust growth and fragmentation cycle dominating the dense disk midplane. The exploration of models shows that extracting planet properties such as mass from observed gap profiles is highly degenerate.
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Vers la compréhension de l’abondance des cyanures / isocyanures : collisions inélastiques et transfert radiatif / Towards the understanding of cyanide/isocyanide abundances : inelastic collisions and radiative transfer calculationsHernandez-Vera, Mario 16 December 2014 (has links)
Les données moléculaires précises, comme les taux de collisions, sont très important pour interpréter les observations de raies moléculaires, et par conséquent, pour estimer la abondance moléculaire dans le milieu interstellaire. Nous avons utilisé différents approximations quantiques pour étudier les excitations rotationnelles de AlCN(1Σ), AlNC(1Σ), MgCN(2Σ), MgNC(2Σ), SiCN(2∏) et SiNC(2∏) à cause des collisions avec atomes de He . On a utilisé He pour simuler les collisions avec H2 en multipliant les taux par un facteur d'échelle. Nous avons aussi étudié le excitation rotationnel de HCN(1Σ) à cause des collisions avec H2. Puis, des calculs de transfert radiatif on été faite pour estimer la abondance relative du isomères dans différentes régions du milieu interstellaire. Malgré les caractéristiques spectroscopiques semblables des isomères, ce travail démontre l'importance d'effectuer des calculs des taux de collisions séparément pour chaque isomère, afin d'obtenir leur abondances. / Accurate molecular data, such collisional rate coefficients, are essential to model molecular lines and then to estimate molecular abundances in the interstellar medium (ISM). For this reason, we have used quantum approximations to study the rotational (de-)excitation of AlCN(1Σ), AlNC(1Σ), MgCN(2Σ), MgNC(2Σ), SiCN(2∏) and SiNC(2∏) molecules by collisions with He, as a model of H2. We have also considered the rotational (de-)excitation of HCN(1Σ) molecules by ortho-H2 and para-H2 molecules.Then, we have performed radiative transfer calculations in order to estimate the relative abundances of cyanide/isocyanide species in the ISM. The impact of our molecular data in the simulation of molecular emissions is discussed. Despite the similar spectroscopic characteristics of the isomers, this work demonstrates the importance of conducting separate collisional rate calculations for each isomer in order to obtain their abundances.
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Spectropolarimetric Signatures of Clumpy Supernova EjectaHole, K. T., Kasen, D., Nordsieck, K. H. 10 September 2010 (has links)
Polarization has been detected at early times for all types of supernovae (SNe), indicating that all such systems result from or quickly develop some form of asymmetry. In addition, the detection of strong line polarization in SNe is suggestive of chemical inhomogeneities ("clumps") in the layers above the photosphere, which may reflect hydrodynamical instabilities during the explosion. We have developed a fast, flexible, approximate semi-analytic code for modeling polarized line radiative transfer within three-dimensional inhomogeneous rapidly expanding atmospheres. Given a range of model parameters, the code generates random sets of clumps in the expanding ejecta and calculates the emergent line profile and Stokes parameters for each configuration. The ensemble of these configurations represents the effects both of various host geometries and of different viewing angles. We present results for the first part of our survey of model geometries, specifically the effects of the number and size of clumps (and the related effect of filling factor) on the emergent spectrum and Stokes parameters. Our simulations show that random clumpiness can produce line polarization in the range observed in SNe Ia, as well as the Q-U loops that are frequently seen in all SNe. We have also developed a method to connect the results of our simulations to robust observational parameters such as maximum polarization and polarized equivalent width in the line. Our models, in connection with spectropolarimetric observations, can constrain the three-dimensional structure of SN ejecta and offer important insight into the SN explosion physics and the nature of their progenitor systems.
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Infrared cooling of the atmosphere by the 9.6 micron band of ozoneSlade, Walter Joseph January 1975 (has links)
Thesis. 1975. M.S.--Massachusetts Institute of Technology. Dept. of Meteorology. / Bibliography: leaves 73-75. / by Walter Joseph Slade, Jr. / M.S.
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Efficient radiative transfer computations in the atmospherePosey, Charles Robert January 1981 (has links)
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Meteorology and Physical Oceanography, 1981. / Microfiche copy available in Archives and Science. / Bibliography: leaves 36-37. / by Charles Robert Posey II. / M.S.
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Use of a Diffusive Approximation of Radiative Transfer for Modeling Thermophotovoltaic SystemsHoffman, Matt J. 19 August 2010 (has links)
No description available.
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Radiative Cooling in Disks and its Effects on the Formation of Giant Planets via the Gravitational InstabilityNero, David J. 08 September 2010 (has links)
No description available.
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A 3-D Monte Carlo Radiative Transfer Model for the Disk of Gamma CassiopeiaeRety, Stephanie R. 09 September 2010 (has links)
No description available.
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