http://hdl.handle.net/1721.1/7654 Thu, 23 May 2013 23:03:18 GMT 2013-05-23T23:03:18Z http://hdl.handle.net/1721.1/78537 Trends and inferred emissions of atmospheric high molecular weight perfluorocarbons Ivy, Diane Jean Atmospheric observations and atmospheric observation-based global emission estimates are presented for the five high molecular weight perfluorocarbons (PFCs): decafluorobutane (C 4 F 1 0 ), dodecafluoropentane (C5 F1 2 ), tetradecafluorohexane (C 6 F14 ), hexadecafluoroheptane (C 7F 16 ) and octadecafluorooctane (C8 F 18 ). Their atmospheric histories are based on measurements of 36 Northern Hemisphere and 46 Southern Hemisphere archived air samples, collected between 1973 and 2011, using two of the "Medusa" cryogenic preconcentration gas chromatography-mass spectrometry instruments, which are part of the Advanced Global Atmospheric Gases Experiment (AGAGE). A new calibration scale was prepared for each PFC, with estimated accuracies of 6.8% for C4Fi0 , 7.8% for C5F12 , 4.0% for CF 14 , 6.6% for C7FE16 and 7.9% for CF8i . Based on our observations, the 2011 globally averaged dry air mole fractions of these high molecular weight PFCs are: 0.17 parts-per-trillion (ppt, i.e., parts per 1012) for C4 F 10 , 0.12 ppt for C5 F 1 2 , 0.27 ppt for CF 1 4 , 0.12 ppt for CFE16 and 0.09 ppt for CF 18 . Newly measured infrared absorption spectra are presented for C7F 16 and CF 1 8 , and using these, their radiative efficiencies and global warming potentials (GWPs) are estimated. We find that the radiative efficiency of C8 F 18 at 0.57Wm- 2 ppb-' is similar to that of trifluoromethyl sulfur pentafluoride's (SF 5 CF 3 ), which has the highest radiative efficiency of any known atmospheric species (Forster et al., 2007). Using their radiative efficiencies, the 2011 observed globally averaged atmospheric mole fractions of the above five high molecular weight PFCs combine to contribute a global average radiative forcing of 0.35 mW m-2, which is 6% of the total anthropogenic PFC radiative forcing (Montzka et al., 2011; Oram et al., 2012). Global emissions for C4 Fio, C5F 12 , C6 F 14 , C7 F 16 and CF 18 were estimated from the observations using a 3-dimensional chemical transport model and a Bayseian inverse method that included a constraint on the annual growth rate of their emissions, consistent with the knowledge of the relevant industries emitting them (Rigby et al., 2011). The derived so-called "top-down" emission estimates show that global emission rates were largest in the 1980s and 1990s for C4 F 10 and C5 F 12 and in the 1990s for C6F 14 , C7F16 and C8F1 . After a subsequent decline, emission rates have remained relatively stable, within ±20 % year-to-year variation, for the last 5 years. Using their calculated 100-year time horizon GWPs, the high molecular weight perfluorocarbons studied here contributed up to 15.4 % of the total PFC emissions expressed in carbon dioxide (C0 2)-equivalents in 1997 and 6 % of the total PFC emissions in 2009. Furthermore, we compare our atmospheric observation-based global emissions to the available so-called "bottom-up" inventories, which are based on production information and end usage. Bottom-up emission estimates are available from the Emission Database for Global Atmospheric Research version 4.2 (EDGARv4.2) for C4F1o, C5 F1 2, C6 F 1 4 and C7F16 , and emission inventories of C4Fio, C5 F1 2 and C6 F14 are also reported to the United Nations' Framework Convention on Climate Change (UNFCCC) by Annex 1 countries that have ratified the Kyoto Protocol (European Commission, Joint Research Centre (JRC)/Netherlands Environmental Assessment Agency (PBL), 2009; United National Framework Convention on Climate Change Secretariat, 2011). The atmospheric observation-based emission estimates are 20 times larger than EDGARv4.2 for C4F10 and over three orders of magnitude larger for C5F1 2 . In contrast, the top-down emission estimates for C6F14 largely agree with the bottom-up estimates from EDGARv4.2. Moreover, the top-down C7 F16 emission estimates are comparable to those of EDGARv4.2 at their peak in the 1990s, albeit with significant underestimation by EDGARv4.2 for the other time periods. There are no bottom-up emission estimates for C8Fi8 , thus the emission rates reported here are the first for this gas. In general, the emission inventories for C4Fio, C5F1 2 and C6F 14 reported to the UNFCCC are five to ten times lower than those estimated in this study from observations. This underreporting to the UNFCCC may be due to only Annex 1 countries reporting inventories and also that some of these countries report a total PFC mixture in C0 2-equivalents, instead of individual PFC emissions rates. Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2012.; Cataloged from PDF version of thesis.; Includes bibliographical references (p. 115-119). Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/1721.1/78537 2012-01-01T00:00:00Z http://hdl.handle.net/1721.1/78477 The roof of the cyclades : a structural, stratigraphic, and paleomagnetic study of Neogene extensional tectonics in Central Greece Bradley, Kyle Edward In this thesis use a variety of geological observations to address the record of Neogene crustal deformation in the Central Aegean region, thereby providing new constraints on the overall geometric and tectonic evolution of an extensional system that is largely governed by the dynamics of a retreating subducting slab. I document a newly-described low-angle normal fault, termed the Octonii Detachment, that accommodated NE-SW directed crustal extension and controlled the pattern of sedimentation within the Early to Middle Miocene Kymi-Aliveri basin. I date the basin fill using a combination of magnetostratigraphy and U/Pb zircon geochronometry. Through detailed mapping of the spatial variation in sedimentary facies within the basin, I relate the record of sedimentation to Middle Miocene extensional exhumation of the metamorphic core complexes exposed in the Cycladic archipelago. In contrast with models of supra-detachment basin development related to fragmentation of the upper plate by arrays of parallel normal faults, I deduce that sedimentation in the Kymi-Aliveri basin occurred in the synformal core of a large-scale, extension-parallel fold. These observations provide direct upper-plate constraints on the timing and kinematics of crustal extension in a region that has been dominated by observations of lower-plate metamorphic rocks. Through paleomagnetic measurement of vertical-axis rotations in Early Miocene through Pliocene basin sequences and associated volcanic rocks, I constrain the initiation of rapid clockwise rotation in Central Greece to post-Early Pliocene time, and infer that Central Greece underwent two pulses of very rapid clockwise rotation separated by a ~10 million year interval of no apparent rotation. This paroxysmal style of deformation contrasts strongly with previous models of long-term, slow rotation driven by gradual trench retreat. I propose a model for the Pliocene deformation of the External Hellenides based on published paleomagnetic data that invokes lateral segmentation of the thrust belt along spaced zones of right-lateral deflection without development of through-going faults at the surface. This analysis attempts to explain how right-lateral motion of an internally stable Aegean Sea block was accommodated between the Kephalonia transform fault and the western prolongation of the North Anatolian Fault. Finally, I use paleomagnetic measurements from a ~3.4 billion year old volcanic and sedimentary succession preserved in the East Pilbara terrane in Western Australia to show that Earth's climate and geomagnetic field geometry could have arisen in a modern form by this time, and that the two oldest well-preserved rock sequences on Earth could in fact be remnants of a single terrane. Thesis (Ph. D. in Geology)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2012.; "September 2012." Cataloged from PDF version of thesis.; Includes bibliographical references. Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/1721.1/78477 2012-01-01T00:00:00Z http://hdl.handle.net/1721.1/78368 Stratosphere - troposphere interaction during stratospheric sudden warming events Domeisen, Daniela I. V. (Daniela Iris Vera) The stratosphere and the troposphere exhibit a strong coupling during the winter months. However, the coupling mechanisms between the respective vertical layers are not fully understood. An idealized spectral core dynamical model is utilized in the present study in order to clarify the coupling timing, location and mechanisms. Since the coupling between the winter stratosphere and troposphere is strongly intensified during times of strong stratospheric variability such as stratospheric warmings, these events are simulated in the described model for the study of stratosphere - troposphere coupling, while for comparison the coupling is also assessed for weaker stratospheric variability. While the upward coupling by planetary-scale Rossby waves in the Northern Hemisphere is well understood, the Southern Hemisphere exhibits traveling wave patterns with a weaker impact on the stratospheric ow. However the tropospheric generation mechanism of these waves is not well understood and is investigated in this study. It is found that in the model atmosphere without a zonally asymmetric wave forcing, traveling waves are unable to induce a significant wave ux into the stratosphere. In the absence of synoptic eddy activity, however, the tropospheric ow is baroclinically unstable to planetary-scale waves, and the generated planetary waves are able to propagate into the stratosphere and induce sudden warmings comparable in frequency and strength to the Northern Hemisphere. While baroclinic instability of long waves may be further strengthened by the addition of moisture, the real atmosphere also exhibits strong synoptic eddy activity, and it will have to be further explored if the atmosphere exhibits periods where synoptic eddies are weak enough to allow for baroclinic instability of long waves. In order to further investigate the coupling between the stratosphere and the troposphere, cases of strong coupling are investigated in the analysis of a Northern Hemisphere - like winter atmosphere. A realistic frequency and strength of sudden warmings is obtained using a zonal wave-2 topographic forcing. An angular momentum budget analysis yields that the Eliassen-Palm (EP) flux is closely balanced by the residual circulation dominated by the Coriolis term on a daily basis, while the change in zonal wind is a small residual between these dominant terms. In the stratosphere, the EP flux term and the Coriolis term balance well in time but not exactly in magnitude, yielding a polar stratospheric weakening of the zonal mean wind as observed during stratospheric warmings. In the troposphere, the loss of angular momentum before a sudden warming induces a weak negative annular mode response, which is amplified by the downward propagating signal about three weeks after the sudden warming. The angular momentum budget does not reveal the mechanism of downward influence, but it nevertheless clarifies the momentum balance of the stratosphere - troposphere system, indicating that the effects of the waves and the residual circulation have to be considered at the same time. Since the annular mode response cannot be directly investigated using the angular momentum budget, the annular mode coupling between the stratosphere and the troposphere is further investigated using a statistical approach. The annular mode response is often framed in terms of Empirical Orthogonal Functions (EOFs), but it is here found that for the stratosphere - troposphere system with its strong vertical pressure gradient, EOFs are strongly dependent on the weighting of the data, while Principal Oscillation Patterns (POPs) are considerably less sensitive to an applied weighting while returning the dominant structures of variability. This encourages further research and application of POP modes for the use of stratosphere - troposphere coupling. These findings represent an improvement of the understanding of stratosphere - troposphere coupling and the results are another step in the direction of finding the mechanism of stratosphere - troposphere coupling and the downward influence after the occurrence of a stratospheric sudden warming, which may influence long-term weather prediction in the troposphere. Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2012.; This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.; Cataloged from student-submitted PDF version of thesis.; Includes bibliographical references (p. 185-192). Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/1721.1/78368 2012-01-01T00:00:00Z http://hdl.handle.net/1721.1/78367 Atlantic Ocean circulation at the last glacial maximum : inferences from data and models Dail, Holly Janine This thesis focuses on ocean circulation and atmospheric forcing in the Atlantic Ocean at the Last Glacial Maximum (LGM, 18-21 thousand years before present). Relative to the pre-industrial climate, LGM atmospheric CO₂ concentrations were about 90 ppm lower, ice sheets were much more extensive, and many regions experienced significantly colder temperatures. In this thesis a novel approach to dynamical reconstruction is applied to make estimates of LGM Atlantic Ocean state that are consistent with these proxy records and with known ocean dynamics. Ocean dynamics are described with the MIT General Circulation Model in an Atlantic configuration extending from 35°S to 75°N at 1° resolution. Six LGM proxy types are used to constrain the model: four compilations of near sea surface temperatures from the MARGO project, as well as benthic isotope records of [delta]¹⁸O and [delta]¹³C compiled by Marchal and Curry; 629 individual proxy records are used. To improve the fit of the model to the data, a least-squares fit is computed using an algorithm based on the model adjoint (the Lagrange multiplier methodology). The adjoint is used to compute improvements to uncertain initial and boundary conditions (the control variables). As compared to previous model-data syntheses of LGM ocean state, this thesis uses a significantly more realistic model of oceanic physics, and is the first to incorporate such a large number and diversity of proxy records. A major finding is that it is possible to find an ocean state that is consistent with all six LGM proxy compilations and with known ocean dynamics, given reasonable uncertainty estimates. Only relatively modest shifts from modern atmospheric forcing are required to fit the LGM data. The estimates presented herein succesfully reproduce regional shifts in conditions at the LGM that have been inferred from proxy records, but which have not been captured in the best available LGM coupled model simulations. In addition, LGM benthic [delta]¹⁸O and [delta]¹³C records are shown to be consistent with a shallow but robust Atlantic meridional overturning cell, although other circulations cannot be excluded. Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2012.; This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.; Cataloged from student-submitted PDF version of thesis.; Includes bibliographical references (p. 221-236). Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/1721.1/78367 2012-01-01T00:00:00Z