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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Diagnosis of mid-latitude synoptic development : a review, and a case study of a developing cyclone

Graham, Richard John January 1991 (has links)
Part I of this thesis is a review of methods for diagnosing synoptic development. Emphasis is placed on the use of the quasi-geostrophic (QG) ω-equation, and on a physical interpretation of the forcing of vertical motion in the QG system. Both the Q-vector formulation (Hoskins, <i>et.al</i>., 1978) and the formulation based on the vertical differential of vorticity advection and horizontal Laplacian of thermal advection (referred to as the VT form), are discussed and compared. Forms of the ω-equation, based on more general balance considerations are also reviewed; specifically the form due to Krishnamurti (1968a), and the geostrophic coordinate semi-geostrophic (SG) form of Hoskins and Draghici (1977). The role of diabatic heating in forcing vertical motion is considered, and a brief discussion of moist symmetric instability is given. The review is placed within the underlying theoretical framework of linear baroclinic instability theory, in the form developed by Eady (1949). Finally, the key concepts underlying the potential vorticity (PV) description of cyclogenesis, reviewed and extended by Hoskins <i>et.al</i>. (1985) are summarised. In part II a case study of the development of the 'hurricane Charley' storm which affected southern England in August 1986 is presented. It is found that the storm developed as a secondary vorticity maximum, which formed on the forward (eastern) side of the old hurricane, was intensified by the action of an upper level trough. The formation and growth of the secondary anomaly, prior to the involvement of the upper trough, is singled out for study. It was found that Sutcliffe techniques were of greater use than PV methods in diagnosing the forward development - with the low-level Q divergence giving the clearest indication of a developing secondary. Separate consideration of the confluent and shear components of the Q-vector forcing is shown to give additional insight. A diagnostic analysis, using ECMWF initialised analyses, revealed that 45-50% of the vorticity growth occurred through forcing associated with large-scale latent heat release. Moreover, latent heat release acts to transfer the locus of development away from the parent low to a position which favours growth of the secondary, and thus controls the character of the development in addition to its intensity. Latent heating is shown to enhance the baroclinic forcing and to influence the onset of 'phase locking' between the secondary and the upper trough. The effects of convection were found to be unimportant in the intensification. The diagnostic analysis is used to show that failure to correctly analyse the structure of the warm moist air mass ahead of the old hurricane circulation was a probable cause of poor 48hr forecasts of the storm.
2

The development and application of techniques for mapping daily minimum air temperatures

Cornford, Dan January 1997 (has links)
Point observations of daily minimum air temperatures, from climate and road weather stations, for the winter 1991-2 are interpolated over Great Britain at 500m resolution. Physical knowledge of the behaviour of the atmosphere identifies those terrain factors having an influence on minimum air temperatures. A Geographic Information System is used to acquire the raw terrain data and create terrain variables based on the terrain factors identified. Exploratory data analysis reveals that some terrain variables have a spatially non-stationary impact on minimum air temperatures. A physically realistic model for mapping the spatial distribution of minimum air temperatures is formulated using a locally varying regression of minimum air temperatures with terrain and a spatially correlated residual component, mapped using geostatistical techniques. The model is optimised and rigorously validated. Results indicate that the local regression of terrain with temperatures does not significantly improve the accuracy of the model compared with a simple global regression. The daily accuracy of the model varied from a root mean square prediction error of O.76°C to 2.27°C (mean error 1.16°C), and this was largely dependent on the synoptic situation. Temperatures at road weather stations were found to differ from those of climate stations. A general framework for interpolating atmospheric variables is proposed. For atmospheric variables the choice of terrain variables used to inform the interpolation is more important than the method of interpolation used. The interpolated surface can then be used in applied atmospheric research, and makes full use of the available atmospheric data, since observing points very rarely correspond to the location (or region) for which the data is required.
3

Teleconnections and transient eddies

Athanasiadis, Panos J. January 2007 (has links)
The subject of this thesis is the dynamics of teleconnections and mid-latitude stationary eddies, key components of the structure and variability of the extratropical general circulation. Deepening our understanding of their dynamics is of particular importance in the context of predicting and explaining possible climate changes.
4

Application of the finite element method to numerical weather prediction

Cullen, Michael John Priestley January 1975 (has links)
The finite element method is applied to wave propagation and advection problems often used to develop models for numerical weather prediction. For these problems the error analysis must distinguish the error in representing the initial and final states from the error in evolution, for instance the error in wave speed. The analysis indicates that finite element methods can only compete with explicit finite difference schemes if "super-convergence" can be obtained. For the Galerkin method this means using splines on a regular or almost regular mesh. This prediction is confirmed in actual tests. Because the finite element approximation provides a complete field rather than gridpoint values alone, the analysis based on it is more meaningful than a gridpoint analysis, there is no "aliasing". The linear spline Galerkin method is then applied to test problems. The high accuracy for given resolution has to be balanced against the extra work involved. For linear problems the results agree with theory. The method is equivalent to an explicit fourth order method with 1.6 times the linear resolution; the efficiency is comparable to explicit finite difference schemes. The nonlinear problems solved include the shallow Water equations in a channel and on a sphere. The finite element algorithm is only competitive if the nonlinear terms involving derivatives are evaluated in two stages. If this is done the integration on a sphere is particularly successful. Artificial viscosity is necessary for realistic problems, the accuracy of the finite element method allows more refined forms of nonlinear viscosity to be used successfully. In general the spline Galerkin method is competitive with explicit finite difference schemes. For nonlinear problems it may give a fundamental improvement, as the spectral method does. However, extreme care has to be taken to get enough accuracy to balance the extra work.
5

Magmatic evolution and the behaviour of volatile species prior to explosive volcanism at Mt. Somma-Vesuvius, Southern Italy

Small, James Alexander January 2007 (has links)
This thesis examines contrasting styles of magmatic differentiation, inferred magma storage conditions and the behaviour of volatile species prior to explosive Plinian and subplinian eruptions at Mt Somma-Vesuvius, southern Italy, Two case-study events are compared: the Plinian eruption of ~3,55 kaBP ('Avellino') and the smaller, more recent subplinian eruption of 472 AD ('Pollena'), These represent opposite end members within the scheme of violently explosive major eruptions at Somma-Vesuvius, in terms of their pre-eruptive repose times, eruptive scenarios, geochemistry and stratigraphic zoning of their juvenile clasts within their fall deposits, The study employs detailed microanalysis of melt inclusions (MI) and their host crystals from the eruptive products of these two events, and compares these new data and observations with published MI and whole-rock data from these and other key eruptions of Somma-Vesuvius, Chapter 2 compares SIMS, Micro-Raman and EPMA measurements of H20 concentration in the same MI and documents the pitfalls of these approaches and the efforts made to mitigate them, In Chapter 3, new and already-published major and trace element data for MI and their host crystals are used to account for clear differences in the degree and style of magmatic (whole-rock) differentiation prior to the two case-study eruptions in terms of differing crystallising assemblages controlling liquid evolution, differing degrees of total fractional crystallisation and relative volumes of the most evolved liquid compositions in the storage system, Chapter 4 reveals that the most evolved magmatic liquids in the Avellino system apparently had higher dissolved water contents than those from Pollena. Relationships between MI H₂0 and CI contents and major and trace elements indicate that magmatic liquids reached saturation with both vapour and brine phases prior to both eruptions and that significant isobaric magmatic differentiation occurred under these volatile-saturated conditions, Maximum H₂O contents and the stability of leucite in Pollena magmas, compared with its total absence from A vellino, are both consistent with shallower storage of the most evolved magmas at around ~ 1 kbar total pressure, compared to ~ 2 kbar for Avellino. A detailed study of sanidine-hyalophane crystals, complex zoning in highly Baand Sr-rich variants, and the relationship between entrapped MI and host-crystal compositions reveals drastic differences in the crystallisation environments recorded by Pollena versus Avellino crystals (Chapter 5). These differences, together with those in bulk-magmatic differentiation and dissolved volatile contents, are interpreted as indications of a relatively mature, deeper and larger volume storage system of highly evolved phonolitic magmas in the case of Avellino, compared to a relatively immature, shallower, complex and smaller volume equivalent for Pollena, Finally an exploratory study (Chapter 5) of sector zoning of Ca, Sr, Ba and Fe in Pollena sanidine-hyalophane crystals implies that, far from being a kinetically controlled disequilibrium feature, there is an intrinsic thermodynamic system control on the strength of apparent intersector partitioning. Temperature is proposed as the most likely control in this case, and the possibility is raised of using this phenomenon for single-crystal thermometry in the future.
6

Coastal zone and climate change management in Oman

Al-Sariri, Thuraiya January 2014 (has links)
Based on an overwhelming body of evidence, there is scientific consensus that global climate is changing and warming of the climate change is unequivocal. Since the 1950's many of the observed changes are unprecedented over decades to millennia (JPCC, 2013). The concentrations of greenhouse gases have increased, the amounts of snow and ice have diminished, sea level has risen and the climate atmosphere and ocean have warmed (IPCC, 2013). However, climate variability and change are considered as important factors for societal developments where they are affecting societies in many ways. In this trend, today, there is new and robust evidence that increased storminess, accelerated sea level rise and coastal erosion as a consequence of global warming are highly likely to have profound impacts on coastal ecosystems and communities worldwide. The occurrences of such consequences are expected to increase in frequency due to the effects of climate change. Globally, different set of scenarios predicted that sea-level would continue to rise between 0.18 to 0;80 cm by 2100. Consistent with global trends, Oman has warmed by ~ 1.03 °C over the last century. There has also been significant inter -annual variability in tropical cyclone frequency and a decrease in precipitation. Additionally, flooding due to storms and tropical cyclones is one of the most devastating naturally hazards in Oman. During the past seven years, Oman experienced two very severe tropical cyclones (Gonu 2007 and Phet 2010), which have affected local economies and communities along the coastal areas. As a result of these changes, attention and awareness has been raised nationally to climate variability and climate change. The main objective of this research is to identify and assess some of the main vulnerable areas of coastal zone of Oman to the climate change implications with particular emphasis on sea level rise. The aims of the study are to: 1) investigate climate and geophysical trends in Oman over the last few decades; 2) assess vulnerable areas of coastal zones of Oman to sea level rise; and 3) assess the current adaptation measures and point out the urgent need to build up institutional and human capacities to approach problems and to indentify gaps, points of strength and points of weakness, options of adaptation and needs for sustainable coastal management plans. This is important for the creation of an effective coastal zone management development strategy that can respond to Climate Change impacts. Thus there is a need to know what is potentially at risks, which lead to the development of a coastal vulnerability index (CVI). The CVI assesses the relatively physical vulnerability to the coast. The study outlines the broad techniques used to determine the CVI for Oman coastlines, which identified zones at risk to sea level rise and assesses its implications for coastal management in Oman. The study shows that AL Batinah and Muscat Governorates are classified as the most highly vulnerable to the impacts of sea level rise because they are most populated and with higher socio-economic activities along their coastlines. However, the findings of this research will be used to define national strategies and policies for climate change adaptation and mitigation for coastal areas.
7

Early meteorological data from London and Paris : extending the North Atlantic Oscillation Series

Cornes, R. C. January 2010 (has links)
It has been known for some time that the potential exists to create long daily series of pressure for the cities of London and Paris by piecing together the barometer readings from various observers and institutions. However, most of the readings prior to 1920 have not previously been digitized or converted to modern units. To rectify this, work began in 2006 to locate and digitize these observations and then to correct the data to form homogeneous series of pressure. Observations have been located to span the years 1670–2007 for Paris and 1692–2007 for London, although significant gaps exist for the periods 1726–47 (Paris) and 1717–22 (London) where no daily pressure observations appear to have survived. The barometer observations were subjected to a quality control procedure before being corrected to represent daily means of sea-level pressure at standard conditions. Statistically significant breakpoints were tested and corrected using the RH-test (version 2). This thesis describes the sources of data used in the London and Paris daily pressure series, and how the data were corrected and homogenized. The new series are compared with previous monthly reconstructions of Mean Sea-Level Pressure (MSLP) for London and Paris. In addition to being of a higher resolution (daily) and stretching over a longer time period than the previous data, the new series resolve certain inhomogeneities apparent in the monthly reconstructions. The daily data are used to construct a westerly index for Europe, which extends instrumental North Atlantic Oscillation (NAO) indices back to the eighteenth century. The relationship of this westerly index to surface temperature across Europe is examined. The results support the findings of previous studies that have indicated non-stationary relationships over time between the atmospheric circulation and surface temperature in the region. The London and Paris series are also used to assess the variability of storminess in the English Channel area over the last 300 years.
8

High resolution palaeoclimatology of the Holocene Sub Polar North Atlantic

Miller, Kathryn Rebecca January 2009 (has links)
A high resolution multiproxy investigation of two marine cores from the Gardar Drift in the Sub Polar North Atlantic, cores MD99-2251 and MD99-2252 has been undertaken to examine the extent of Holocene climate variability reflected by changes in diatom floral abundances and ice rafted debris flux. The results from this study provide both an overview of climate variability for the entire Holocene as recorded in the Sub Polar North Atlantic and a detailed high resolution study focussed around the 8.2kyr event. Sea surface temperature (SST) estimates are derived using a weighted average partial least squares (WAPLS) transfer function and a new regionally based diatom transfer function developed as part of this study. Principal component analysis and K-means cluster analysis were undertaken on core MD99-2251 to identify floral groupings within the diatom taxa. The changing composition of diatom assemblages and SST records indicate a highly unstable early Holocene from 11.5 to 9.5kyr with switches in the dominance of cool Sub Arctic floras and warmer North Atlantic floras. The presence of high productivity events in the diatom floras during this interval suggests that the core locations were, at times, in close proximity of the Sub Arctic Front. A broad SST cooling from 9.5 to 7kyr is identified followed by a pronounced warming for 7 to 5kyr and more stable but cooler temperatures during the Late Holocene. Changes in sea surface hydrography, especially the relative strength of the warm Irminger Current, is considered to have had the greatest influence on the composition of diatom floral assemblages. The 8.2kyr event is not recognised as a discrete climate perturbation in either the diatom assemblage data or the IRD record, but is contained within the broad cooling event from 9.5-7kyr. Analysis of sea-ice and cold water flora however does indicate some increase in these species for the interval 8.8 to 7.8kyr.
9

Fine resolution modelling of ammonia dry deposition over Great Britain

Singles, Roderick John January 1996 (has links)
In this study an alternative has been taken, by applying an atmospheric transport model. Due to assumptions in the treatment of vertical dispersion, many current UK models are unable to describe the short-range dispersion of ammonia adequately, so a new statistical model has been created by extensively modifying an existing Lagrangian trajectory model. A number of atmospheric processes have been parameterised for inclusion in the model, and boundary data have been constructed to allow the inclusion of continental emissions. The wind speed data used to advect the model have been optimised for NH<SUB>3</SUB> dry deposition, and careful restructuring of the computer code has reduced computational time considerably. Initial testing of the model on a 20 km x 20 km grid has shown that modelled wet deposition fluxes of sulphate and nitrate have a fair degree of success in reproducing measurement data. Comparisons of SO<SUB>2</SUB> and NO<SUB>2</SUB> surface concentrations with measured data have shown a variable degree of success, highlighting the uncertainties in emission heights. A number of sensitivity tests have been performed on various models processes, and have shown the degree of dependence of certain modelled species on the type of parameterisation used in the model. Emissions data for NH<SUB>3</SUB> have been employed on a much finer horizontal scale of 5 km x 5 km grid squares than has been previously used in an atmospheric transport model over Great Britain. The use of a detailed description of vertical diffusion and dry deposition, together with a fine resolution emissions dataset, have produced the best yet agreement with measured NH<SUB>3</SUB> surface concentration estimates for Great Britain. Total annual fluxes of NH<SUB>3</SUB> dry deposition agree well with official estimates, but the spatial distribution of these data differ considerably, and highlight the possible over-estimation of the NH<SUB>3</SUB> samplers used in the monitoring network in areas of very low surface concentrations. A total annual budget for reduced nitrogen is given which shows the directional-dependence of both total deposition and export of reduced nitrogen. The model estimates that on average over half of the total dry deposition is the result of emissions being dry deposited in the same 5 km grid square. The spatial variation of this fraction is important information which can be used to guide emission reduction strategies.
10

Planetary wave activity in the stratosphere

Li, Dingmin January 1991 (has links)
This thesis presents a diagnostic study into some aspects of stratospheric dynamics, from seeking a better approximation of winds using satellite derived data to the dynamics of wave activity and wave-mean flow interaction with the aid of newly developed theory. An approximation scheme named 'quasi-geostrophic wind', is tested and its merits discussed by comparison and contrast with some currently common used methods, vis. geostrophic, linear balance, nonlinear balance winds. The dynamical behaviour of the stratosphere is diagnosed, using LIMS data, in the form of definition of wave activity density given by Andrews (1987) and in terms of the generalized Eliassen- Palm flux theorem. As the theory is strictly applicable only to small amplitude waves, the study is mainly concentrated on a period of low wave activity in late Autumn. There is good agreement in the changes of terms of the generalized Eliassen-Palm flux theorem. Time-latitude plots of Eliassen-Palm flux divergence, wave activity density and its rate of change, together with wave dissipation show a day to day coherence. A good qualitative agreement is also found between the change of zonal mean wind and wave activity in accordance with the theorem. The balance among the terms in the theorem is only approximate, an indication of importance of nonlinear effects neglected in the linear premise. The balance is improved when the non conservative term is included. An analogous expression to the generalized Eliassen-Palm flux theorem but for chemical tracers is derived theoretically and a corresponding wave activity defined in terms of chemical tracers such as ozone is presented. This analogous expression shows the relation between the tracer transport and the wave transience; after some simplifications this gives a novel method of estimating the transport coefficients. In the middle atmosphere good agreement is found between wave activity defined in terms of ozone mixing ratio with that defined in terms of potential vorticity. Results of an attempt to estimate transport coefficients by tracer wave transiences and the corresponding parameterized flux are also presented and the contribution due to dispersion is discussed. The estimation by this method is found capable of reflecting the large effects of wave dispersion in late winter. The transport coefficients from dispersion of fluid parcels alone are not fully satisfactory due to appearance of a large area of negative coefficients in the monthly mean plots which may be caused by the limit of linear theory, the effects of chemical eddies (sources and sinks) or by the errors in the data that may hinder our estimation of wave transience.

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