745 research outputs found
The ascending prayer to Christ: theodore Stoudite's defence of the Christ-єikwv against ninth century iconoclasm
No full textTheodore Stoudite (759-826) was at the centre of a revival of patristic learning which equipped him to apply the weight of the Christian tradition to the Byzantine image controversy of the eighth and ninth centuries. In this recovery of the tradition Theodore discovered how the epistemological and ontological demands of both radical divine transcendence and divine active agency in the creative order are met in the incarnate Christ. He concluded that the liturgical expression of this developed theology requires the presence of the Christ- єikwv. The structure of this thesis reflects the single argument of the three-part ‘Avtρρητικοι κατα єικουομάxwv(c. 816). Antirr I and II describe the content of the 754 and 787 Councils, revealing the causes of the theological impasse which prevented the resolution of the controversy. In Antirr I and II Theodore also establishes the ground for his argument in Antirr III by distancing the eighth century Christ- єikwv from its function in former centuries as symbol, pure narrative painting and relic. Theodore defines its contemporary function as liturgical, devotional and doctrinal in character. Written in response to the 815 Council, Antirr III is Theodore's apology for this Christ- єikwv as a legitimate object of лροσκύvησs-. The argument is established within the parameters of the tradition as Theodore carefully defends the circumscribability of Christ in accordance with Chalcedonian Christology. My analysis of the Antirr, assisted by a reading of his letters, reveals that Theodore understands the Christ- єikwv as playing a key role both in the ascetic struggle to free the mind from λογισμοι (distracting thoughts), and in the practice of θєwρια(contemplation) within the Liturgy. The liturgical, doctrinal and devotional Christ- єikwv has become a revealed and formal means by which the worshipper receives a Dionysian άυαγwγη(spiritual uplifting) to the divine presence
sj-pdf-1-ppg-10.1177_03091333221079201 – Supplemental Material for Tracking the methodological evolution of climate change projections for UK river flows
No full textSupplemental Material, sj-pdf-1-ppg-10.1177_03091333221079201 for Tracking the methodological evolution of climate change projections for UK river flows by Wilson CH Chan, Theodore G Shepherd, Katie Facer-Childs, Geoff Darch and Nigel W Arnell in Progress in Physical Geography: Earth and Environment</p
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Lateral boundary contributions to wave-activity invariants and nonlinear stability theorems for balanced dynamics
No full textThe slow advective-timescale dynamics of the atmosphere and oceans is referred to as balanced dynamics. An extensive body of theory for disturbances to basic flows exists for the quasi-geostrophic (QG) model of balanced dynamics, based on wave-activity invariants and nonlinear stability theorems associated with exact symmetry-based conservation laws. In attempting to extend this theory to the semi-geostrophic (SG) model of balanced dynamics, Kushner & Shepherd discovered lateral boundary contributions to the SG wave-activity invariants which are not present in the QG theory, and which affect the stability theorems. However, because of technical difficulties associated with the SG model, the analysis of Kushner & Shepherd was not fully nonlinear.
This paper examines the issue of lateral boundary contributions to wave-activity invariants for balanced dynamics in the context of Salmon's nearly geostrophic model of rotating shallow-water flow. Salmon's model has certain similarities with the SG model, but also has important differences that allow the present analysis to be carried to finite amplitude. In the process, the way in which constraints produce boundary contributions to wave-activity invariants, and additional conditions in the associated stability theorems, is clarified. It is shown that Salmon's model possesses two kinds of stability theorems: an analogue of Ripa's small-amplitude stability theorem for shallow-water flow, and a finite-amplitude analogue of Kushner & Shepherd's SG stability theorem in which the ‘subsonic’ condition of Ripa's theorem is replaced by a condition that the flow be cyclonic along lateral boundaries. As with the SG theorem, this last condition has a simple physical interpretation involving the coastal Kelvin waves that exist in both models.
Salmon's model has recently emerged as an important prototype for constrained Hamiltonian balanced models. The extent to which the present analysis applies to this general class of models is discussed
MANOVA modelling of a chiropractic longitudinal study using multiple imputation
No full textThe purpose of this report is to present the detailed statistical analysis of a randomised, placebo-controlled trial comparing two different treatment modalities to an intervention of no known benefit for people with acute or subacute thoracic spine pain.
The therapy arms consist of Spinal Manipulative Therapy (SMT) and Graston Technique (GT) and the placebo is a non-functional ultrasound. A placebo group was utilised because at present there are no proven treatments for non-specific thoracic pain. This trial is registered with the Australia and New Zealand Clinical Trials Registry. Ethics approval has been granted by Murdoch University Human Research and Ethics Committee, number 2007/274.
The aim of this three arm trial was to test the efficacy of SMT and GT as independent modalities compared to detuned ultrasound for the outcomes of pain and disability. The latter were measured using the Visual Analogue Scale (VAS) and a modified Oswestry Back Pain Disability Index. The study was conducted at the Murdoch University Chiropractic student clinic in Perth, Australia, and the protocol published in Crothers et al (2008).
In this report, Section 2 provides an initial exploratory analysis of the data, Section 3 outlines the statistical models used in the final analysis, Section 4 defines these models in mathematical terms, Section 5 discusses the management of missing values via multiple imputation and Section 6 presents the results of the statistical modelling and hypothesis tests. The clinical study will be published in full elsewhere
The Arctic Polar-night Jet Oscillation
No full textThe eastward winds that form each winter in the Arctic stratosphere are intermittently disrupted by planetary-scale waves propagating up from the surface in events known as stratospheric sudden warmings. It is shown here that following roughly half of these sudden warmings, the winds take as long as three months to recover, during which time the polar stratosphere evolves in a robust and predictable fashion. These extended recoveries, termed here Polar-night Jet Oscillation (PJO) events, are relevant to understanding the response of the extratropical troposphere to forcings such as solar variability and climate change. They also represent a possible source of improvement in our ability to predict weather regimes at seasonal timescales.
Four projects are reported on here. In the first, the approximation of stratospheric radiative cooling by a linear relaxation is tested and found to hold well enough to diagnose effective damping rates. In the polar night, the rates found are weaker than those typically assumed by simplified modelling studies of the extratropical stratosphere and troposphere. In the second, PJO events are identified and characterized in observations, reanalyses, and a comprehensive chemistry-climate model. Their observed behaviour is reproduced well in the model. Their duration correlates with the depth in the stratosphere to which the disruption descends, and is associated with the strong suppression of further planetary wave propagation into the vortex. In the third, the response of the zonal mean winds and temperatures to the eddy-driven torques
that occur during PJO events is studied. The collapse of planetary waves following the initial warming permits radiative processes to dominate. The weak radiative damping rates diagnosed in the first project are required to capture the redistribution of angular momentum responsible for the circulation anomalies. In the final project, these damping rates are imposed in a simplified model of the coupled stratosphere and troposphere. The weaker damping is found
to change the warmings generated by the model to be more PJO-like in character.
Planetary waves in this case collapse following the warmings, confirming the
dual role of the suppression of wave driving and extended radiative timescales
in determining the behaviour of PJO events.Ph
The Applicability of Kraichnan-Leith-Batchelor Similarity Theory to Inverse Cascades in Generalized Two-Dimensional Turbulence
No full textThis thesis examines how well Kraichnan-Leith-Batchelor (KLB) similarity theory describes turbulent inverse cascades in `generalized two-dimensional fluids', also known as ` turbulence' models. These models have varying relationships between the streamfunction and advected active scalar = (-)Ph.D.2015-12-16 00:00:0
Influence of the Quasi-biennial Oscillation on Interannual Variability in the Northern Hemisphere Winter Stratosphere
No full textObservations show that the interannual variability of the Northern Hemisphere (NH) extratropical winter stratosphere is strongly correlated with the quasi-biennial oscillation (QBO) of tropical stratospheric winds, particularly during early winter. Most current general circulation models (GCMs) do not exhibit a QBO and therefore do not represent this important mode of tropical-extratropical interaction. In this study we examine the QBO-extratropical correlation using a 150-year GCM simulation in which a QBO occurs.
Since no external forcings or interannual variations in sea surface temperatures are imposed, the modelled tropical-extratropical interactions represent an internal mode of atmospheric variability. The QBO itself is spontaneously forced by a combination of resolved and parameterized waves. The effects of this QBO on the climatological mean state and its interannual variability are considered, both by comparison with a control simulation (also 150 years in length, but with no QBO) and by compositing winters according to the phase of the QBO. Careful attention is given to the definition of QBO phase. Comparisons of the model results with observations (reanalysis data) are also made.
QBO-induced changes in the climatological state of the model are found to have high statistical significance above the tropopause. In the extratropical winter stratosphere, these mean-state changes arise predominantly from the influence of the QBO on the propagation and dissipation of planetary-scale waves. This behaviour is shown to depend on the seasonal cycle, which argues for the usefulness of considering tropical-extratropical interactions in a GCM context. QBO influence on the interannual variability of the extratropical winter stratosphere is also seasonal, and the tropical-extratropical interaction is sensitive to the phase alignment of the QBO with respect to the annual cycle. This phase alignment is strongly affected by the seasonality of QBO phase transitions, which - due to the QBO being spontaneously generated, rather than having an imposed period - is somewhat realistic in the model. This leads to fluctuations in the strength of the modelled tropical-extratropical interaction occurring on a decadal timescale as an internal mode of atmospheric variability.Ph
The Applicability of Kraichnan-Leith-Batchelor Similarity Theory to Inverse Cascades in Generalized Two-Dimensional Turbulence
No full textThis thesis examines how well Kraichnan-Leith-Batchelor (KLB) similarity theory describes turbulent inverse cascades in `generalized two-dimensional fluids', also known as ` turbulence' models. These models have varying relationships between the streamfunction and advected active scalar = (-)Ph.D.2015-12-16 00:00:0
Energy and Momentum Consistency in Subgrid-scale Parameterization for Climate Models
No full textThis thesis examines the importance of energy and momentum consistency in subgrid-scale parameterization for climate models. It is divided into two parts according to the two aspects of the problem that are investigated, namely the importance of momentum conservation alone and the consistency between energy and momentum conservation. The first part addresses the importance of momentum conservation alone. Using a zonally-symmetric model, it is shown that violating momentum conservation in the parameterization of gravity wave drag leads to large errors and non-robustness of the response to an imposed radiative perturbation in the middle atmosphere. Using the Canadian Middle Atmosphere Model, a three-dimensional climate model, it is shown that violating momentum conservation, by allowing gravity wave momentum flux to escape through the model lid, leads to large errors in the mean climate when the model lid is placed at 10 hPa. When the model lid is placed at 0.001 hPa the errors due to nonconservation are minimal. When the 10 hPa climate is perturbed by idealized ozone depletion in the southern hemisphere, nonconservation is found to significantly alter the polar temperature and surface responses. Overall, momentum conservation ensures a better agreement between the 10 hPa and the 0.001 hPa climates.
The second part addresses the self-consistency of energy and momentum conservation. Using Hamiltonian geophysical fluid dynamics, pseudoenergy and pseudomomentum wave-activity conservation laws are derived for the subgrid-scale dynamics. Noether’s theorem is used to derive a relationship between the wave-activity fluxes, which represents a generalization of the first Eliassen-Palm theorem. Using multiple scale asymptotics a theoretical framework for subgrid-scale parameterization is built which consistently conserves both energy and momentum and respects the second law of thermodynamics. The framework couples a hydrostatic resolved-scale flow to a non-hydrostatic subgrid-scale flow. The transfers of energy and momentum between the two scales are understood using the subgrid-scale wave-activity conservation laws, whose relationships with the resolved-scale dynamics represent generalized non-acceleration theorems. The derived relationship between the wave-activity fluxes — which represents a generalization of the second Eliassen-Palm theorem — is key to ensuring consistency between energy and momentum conservation. The framework includes a consistent formulation of heating and entropy production due to kinetic energy dissipation.Ph
The Arctic Polar-night Jet Oscillation
No full textThe eastward winds that form each winter in the Arctic stratosphere are intermittently disrupted by planetary-scale waves propagating up from the surface in events known as stratospheric sudden warmings. It is shown here that following roughly half of these sudden warmings, the winds take as long as three months to recover, during which time the polar stratosphere evolves in a robust and predictable fashion. These extended recoveries, termed here Polar-night Jet Oscillation (PJO) events, are relevant to understanding the response of the extratropical troposphere to forcings such as solar variability and climate change. They also represent a possible source of improvement in our ability to predict weather regimes at seasonal timescales.
Four projects are reported on here. In the first, the approximation of stratospheric radiative cooling by a linear relaxation is tested and found to hold well enough to diagnose effective damping rates. In the polar night, the rates found are weaker than those typically assumed by simplified modelling studies of the extratropical stratosphere and troposphere. In the second, PJO events are identified and characterized in observations, reanalyses, and a comprehensive chemistry-climate model. Their observed behaviour is reproduced well in the model. Their duration correlates with the depth in the stratosphere to which the disruption descends, and is associated with the strong suppression of further planetary wave propagation into the vortex. In the third, the response of the zonal mean winds and temperatures to the eddy-driven torques
that occur during PJO events is studied. The collapse of planetary waves following the initial warming permits radiative processes to dominate. The weak radiative damping rates diagnosed in the first project are required to capture the redistribution of angular momentum responsible for the circulation anomalies. In the final project, these damping rates are imposed in a simplified model of the coupled stratosphere and troposphere. The weaker damping is found
to change the warmings generated by the model to be more PJO-like in character.
Planetary waves in this case collapse following the warmings, confirming the
dual role of the suppression of wave driving and extended radiative timescales
in determining the behaviour of PJO events.Ph
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