Global ETD Search

1	Quasi-Biennial Oscillation och dess påverkan på klimatet i troposfären / The Quasi-Biennial Oscillation and its Effects on the Tropospheric Climate Oliver, Nordvall January 2018 (has links) The Quasi-Biennial Oscillation (QBO) is the strongest phenomena influencing the stratopheric (~15-50 km height) circulation over the equator. QBO has two phases of downward propagating easterly and westerly winds, which has a total period of approximately 28 months and the phase is defined by the wind direction between the airpressure 25-50 hPa, which is roughly at a height of 30 km. QBO is induced by atmospheric gravity waves originating from the troposphere (~0-15 km height) and are generated by a plethora of sources, such as tropical convection and wind shear. The winds propagate downward at about 1 km per month through the stratosphere until reaching the tropopause (~15 km height) where they dissipate. The wind speed is at its maximum in the middle of the phase, where the wind shear is at its lowest, and the easterly winds can grow up to 30 m/s whilst the westerly winds reach roughly 15 m/s. Although the QBO is an equatorial phenomena it has a poleward component radiating its signal from the tropics to the higher latitudes where it affects other circulations such as the stratospheric polar vortex on the northern hemisphere (NH). The polar vortex consists of westerly winds around the polar region and is a major influence on the winter climate on the NH and thereby allows the QBO to indirectly affect the tropospheric climate through it. The easterly QBO disturbs and weakens the polar vortex, which results in warm subtropical air penetrating the vortex and warming the Arctic region whereas the polar air is released southward creating a colder winter on the NH. The westerly QBO on the other hand enhances the polar vortex and contains the cool polar air over the Arctic, which results in a milder winter. The correlation between QBO and El Niño Southern Oscillation (ENSO) as well as the tropical cyclones (TC) has either changed (ENSO) or completely disappeared (TC). The ENSO-QBO correlation depends on which phase of ENSO coincide with which phase of QBO, where El Niño coinciding with easterly QBO and La Niña coinciding with westerly QBO results in wind anomalies in the NH stratosphere. If the opposite combination takes place the wind anomalies will instead be situated in the subtropical troposphere, displacing the subtropical jet poleward. To what extent these stratospheric winds exert their influence is to some degree still uncertain, but that they have an effect on the tropospheric climate is unbeknownst to no one. / Cirkulationen i den ekvatoriella stratosfären (ca 15-50 km höjd) domineras av Quasi-Biennial Oscillation (QBO), ett zonalt (parallellt ekvatorn) vindfenomen med två faser bestående av östliga respektive västliga vindar och en period på ca 28 månader. Fasen definieras mellan lufttrycken 25-50 hPa, vilket representerar en höjd på ca 30 km. Drivkraften bakom QBO är ett brett spektrum av atmosfäriska gravitationsvågor som skapas genom bland annat den tropiska konvektionen, vindskjuvning och frontsystem. Vindarna propagerar vertikalt nedåt genom stratosfären med ungefär 1 km per månad tills de når tropopausen (ca 15 km) där vindarna försvagas kraftigt till ett zonalt medelvärde på 0 m/s. Vindhastigheten under östlig QBO uppgår i ca 30 m/s medan västlig QBO uppgår i ca 15 m/s, och är maximal i höga stratosfären samt i mitten av faserna där vindskjuvningen är minimal. QBO sprider sig meridionalt (nord-syd) från tropikerna till högre breddgrader genom stratosfären där andra fenomen som den stratosfäriska polarvirveln kan påverkas på norra halvklotet (NH). Polarvirveln består av västliga vindar i stratosfären runt polarregionen och är en stor influens på vinterklimatet i framförallt Europa och Nordamerika. Genom polarvirveln kan QBO indirekt påverka klimatet i troposfären (ca 0-15 km), där den östliga fasen av QBO försvagar medan den västliga fasen av QBO förstärker polarvirveln. En försvagad polarvirvel innebär en varmare medeltemperatur på Arktis och att kallare polarluft söker sig söderut och orsakar kalla vintertemperaturer. Troposfäriska klimatfenomen som El Niño Southern Oscillation (ENSO) och tropiska cykloner (TC) har uppvisat ett samband till QBO, men sedan förändrats (ENSO) eller helt försvunnit (TC). ENSO-QBO korrelationen förändras beroende på vilken fas QBO respektive ENSO är i relativt varandra. Då El Niño sammanfaller med östliga QBO samt La Niña sammanfaller med västliga QBO uppstår vindanomalier vid höga latituder i NH:s stratosfär, medan vid omvända sambandet förflyttar sig vindanomalierna till subtropikerna i troposfären och kan där förskjuta den subtropiska jetströmmen norrut. Att de stratosfäriska vindarna påverkar troposfären är känt, men hur och till vilken grad är ännu inte uppenbart. På grund av den korta tidsperiod med kontinuerliga och tillförlitliga vindmätningar i stratosfären uppkommer flera hypotetiska effekter av QBO och dess påverkan på klimatet i troposfären. Quasi-Biennial Oscillation QBO Climate Polar Vortex ENSO TC Holton-Tan Effect Quasi-Biennial Oscillation QBO Klimat Polarvirvel ENSO TC Holton-Tan Effect Meteorology and Atmospheric Sciences Meteorologi och atmosfärforskning
2	Tropical stratosphere variability and extratropical teleconnections Schenzinger, Verena January 2016 (has links) The Quasi-Biennial Oscillation (QBO) is the dominant pattern of variability in the tropical stratosphere. Despite a well established theory regarding its generation in the atmosphere, the simulation in global climate models remains difficult. A set of metrics assessing the quality of model simulations is presented in this study. The QBO simulations in models submitted to the CMIP5 and CCMVal-2 intercomparison projects are characterised and compared to radiosonde observations and reanalysis datasets. Common model biases and their potential causes are addressed. As the QBO has a long intrinsic period, knowing its influences on other parts of the climate system can be used to improve long range forecasts. These teleconnections of the QBO in observations are investigated using composite analysis, multilinear regression and a novel approach called causal effect networks (CEN). Findings from these analyses confirm previous results of the QBO modulating the stratospheric polar vortex and subsequently the North Atlantic Oscillation (NAO). They also suggest that it is important to take the equatorial zonal mean zonal wind vertical profile into account when studying teleconnections, rather than the more traditional method of using just one single level. While QBO influences on the Northern Hemisphere winter polar vortex and the NAO are more clearly established, interactions within the tropics remain inconclusive. Regression analysis does not show a connection between the QBO and the MJO, whereas the CEN analysis does. Further studies are needed to understand the interaction mechanisms near the equator. Finally, following the unprecedented disruption of the QBO cycle in the winter 2015/16, the event is described and a model analogue from the MPI-ESM-MR historical simulation is presented. Future implications are unclear, although model projections indicate more frequent QBO irregularities in a warming climate.
3	The influence of the quasi-biennial oscillation on the stratospheric polar vortices Watson, Peter Alan Gazzi January 2013 (has links) The mean strengths of the wintertime stratospheric polar vortices are known to be related to the phase of the quasi-biennial oscillation (QBO) in the tropical stratosphere from circulation statistics - the "Holton-Tan relationship". The principal topic of this thesis is improving understanding of the mechanism behind the QBO's influence. Following the example of previous studies, the QBO influence on the Northern Hemisphere (NH) extratropics on monthly time scales in an observational reanalysis is examined, and is shown to closely resemble the stratospheric Northern annular mode (NAM). It is argued that this may not be informative about the mechanism, as the response could be NAM-like for many different mechanisms. It is suggested that examining the transient response of the NH extratropics to forcing by the QBO would be much more informative, particularly on time scales of a few days. In a primitive equation model of the middle atmosphere, the long-term stratospheric NH response to imposed zonal torques is often found to be NAM-like under perpetual January conditions, with wave feedbacks making a very important contribution. However, the response in runs with a seasonal cycle is not NAM-like. Investigation of the transient responses indicates the wave feedbacks are qualitatively similar in each case but only strong enough under perpetual January conditions to make the long-term response NAM-like. This supports the hypothesis that feedbacks from large-scale dynamics tend to make the stratospheric response to arbitrary forcings NAM-like, and therefore indicates that the long-term response is not generally useful for understanding forcing mechanisms. Examining the short-term transient response to known torques is found to be more successful at inferring information about the torques than several other previously proposed methods. Finally, the short-term transient response of the NH extratropics to forcing by the easterly QBO phase in a general circulation model is found to be consistent with the proposed mechanism of Holton and Tan (1980), indicating that this mechanism plays a role in the Holton-Tan relationship. 551.51
4	HF Radar Observations of Inter-Annual variations in Mid-Latitude Mesospheric Winds Malhotra, Garima 15 June 2016 (has links) The equatorial Quasi Biennial Oscillation (QBO) is known to be an important source of inter-annual variability at mid and high latitudes in both hemispheres. Coupling between QBO and the polar vortex has been extensively studied over the past few decades, however, less is known about QBO influences in the mid-latitude mesosphere. One reason for this is the relative lack of instrumentation available to study mesospheric dynamics at mid-latitudes. In this study, we have used the mid-latitude SuperDARN HF radar at Saskatoon (52.16 N, -106.53 E) to study inter-annual variation in mesospheric winds. The specific aim was to determine whether or not a Quasi Biennial signature could be identified in the Saskatoon mesosphere, and if so, to understand its relationship with the equatorial stratospheric QBO. To achieve this goal, a technique has been developed which extracts meteor echoes from SuperDARN near-range gates and then applies least-squares fitting across all radar beam directions to calculate hourly averages of the zonal and meridional components of the mesospheric neutral wind. Subsequent analysis of 13 years (2002-2014) of zonal wind data produced using this technique indicates that there is indeed a significant QBO signature present in Saskatoon mesospheric winds during late winter (Jan-Feb). This mesospheric QBO signature is in opposite phase with the equatorial stratospheric QBO, such that when QBO (at 50 hPa) is in its easterly (westerly) phase, the late winter winds in Saskatoon mesosphere become more (less) westerly. To further examine the source of the signature, we also analyzed winds in the Saskatoon stratosphere between 5 hPa and 70 hPa using the ECMWF ERA-Interim reanalysis data set, and found that the late winter stratospheric winds become less (more) westerly when QBO is easterly (westerly). This QBO signature in the mid-latitude stratospheric winds is essentially the same as that observed for the polar vortex in previous studies but it is opposite in phase to the mid-latitude mesospheric QBO. We therefore conclude that filtering of gravity waves through QBO-modulated stratospheric winds plays a major role in generating the mesospheric QBO signature we have identified in the Saskatoon HF radar data. When the Saskatoon stratospheric winds are anomalously westward during easterly QBO, the gravity waves having westward momentum might be filtered out, depositing a net eastward momentum in the mesosphere as they propagate upwards. This would result in increased westerly mesospheric winds at Saskatoon. The opposite would happen when the equatorial QBO is westerly. / Master of Science HF Radar Meteor echoes SuperDARN radar Gravity wave filtering Mesospheric QBO Mid-Latitude QBO Holton Tan SuperDARN Radar Mesospheric winds
5	Overeating, Obesity, and Weakness of the Will Sommers, Jennifer Heidrun 28 August 2015 (has links) The philosophical literature on akrasia and/or weakness of the will tends to focus on individual actions, removed from their wider socio-political context. This is problematic because actions, when removed from their wider context, can seem absurd or irrational when they may, in fact, be completely rational or, at least, coherent. Much of akrasia's apparent mystery or absurdity is eliminated when people's behaviours are considered within their cultural and political context. I apply theories from the social and behavioural sciences to a particular behaviour in order to show where the philosophical literature on akrasia and/or weakness of the will is insightful and where it is lacking. The problem used as the basis for my analysis is obesity caused by overeating. On the whole, I conclude that our intuitions about agency are unreliable, that we may have good reasons to overeat and/or neglect our health, and that willpower is, to some degree, a matter of luck. / Graduate / 0630 / 0573 / 0422 / felshereeno@aol.com akrasia action theory addiction agency Alison McIntyre applied ethics Bernard Williams body studies Bourdieu Cartesian dualism Christine Korsgaard compulsion continence deviance diet Distinction Donald Davidson dualism externalism incontinence inequality internalism intuition Irving K. Zola Marx medicalization morality Nichomachean Ethics Nomy Arpaly obesity epidemic orthorexia overeating overweight personal identity Petr Skrabanek Philip Kitcher philosophical intuition picoeconomics Pierre Bourdieu fat free will Gary Watson George Ainslie habitus healthism rat park rational choice rationality Richard Holton Robert Crawford social class stigma taste for luxury temperance utility maximization virtue weakness of the will willpower
6	The Social Construction of Economic Man: The Genesis, Spread, Impact and Institutionalisation of Economic Ideas Mackinnon, Lauchlan A. K. Unknown Date (has links) The present thesis is concerned with the genesis, diffusion, impact and institutionalisation of economic ideas. Despite Keynes's oft-cited comments to the effect that 'the ideas of economists and political philosophers, both when they are right and when they are wrong, are more powerful than is commonly understood'(Keynes 1936: 383), and the highly visible impact of economic ideas (for example Keynesian economics, Monetarism, or economic ideas regarding deregulation and antitrust issues) on the economic system, economists have done little to systematically explore the spread and impact of economic ideas. In fact, with only a few notable exceptions, the majority of scholarly work concerning the spread and impact of economic ideas has been developed outside of the economics literature, for example in the political institutionalist literature in the social sciences. The present thesis addresses the current lack of attention to the spread and impact of economic ideas by economists by drawing on the political institutionalist, sociological, and psychology of creativity literatures to develop a framework in which the genesis, spread, impact and institutionalisation of economic ideas may be understood. To articulate the dissemination and impact of economic ideas within economics, I consider as a case study the evolution of economists' conception of the economic agent - "homo oeconomicus." I argue that the intellectual milieu or paradigm of economics is 'socially constructed' in a specific sense, namely: (i) economic ideas are created or modified by particular individuals; (ii) economic ideas are disseminated (iii) certain economic ideas are accepted by economists and (iv) economic ideas become institutionalised into the paradigm or milieu of economics. Economic ideas are, of course, disseminated not only within economics to fellow economists, but are also disseminated externally to economic policy makers and business leaders who can - and often do - take economic ideas into account when formulating policy and building economic institutions. Important economic institutions are thereby socially constructed, in the general sense proposed by Berger and Luckmann (1966). But how exactly do economic ideas enter into this process of social construction of economic institutions? Drawing from and building on structure/agency theory (e.g. Berger and Luckmann 1966; Bourdieu 1977; Bhaskar 1979/1998, 1989; Bourdieu 1990; Lawson 1997, 2003) in the wider social sciences, I provide a framework for understanding how economic ideas enter into the process of social construction of economic institutions. Finally, I take up a methodological question: if economic ideas are disseminated, and if economic ideas have a real and constitutive impact on the economic system being modelled, does 'economic science' then accurately and objectively model an independently existing economic reality, unchanged by economic theory, or does economic theory have an interdependent and 'reflexive' relationship with economic reality, as economic reality co-exists with, is shaped by, and also shapes economic theory? I argue the latter, and consider the implications for evaluating in what sense economic science is, in fact, a science in the classical sense. The thesis makes original contributions to understanding the genesis of economic ideas in the psychological creative work processes of economists; understanding the ontological location of economic ideas in the economic system; articulating the social construction of economic ideas; and highlighting the importance of the spread of economic ideas to economic practice and economic methodology. 410401 Design Theory 349901 Political Economy 370000 Studies in Human Society 340302 History of Economic Thought 349900 Other Economics 410402 Design Innovation 360201 Public Policy 360000 Policy and Political Science 380100 Psychology 360100 Political Science 360200 Policy and Administration 370101 Social Theory 370102 Social Policy and Planning 340100 Economic Theory genesis spread diffusion impact institutionalisation economic ideas idea ideation psychology of creativity Wallas Wertheimer stage model productive thinking creative creativity process economic economics sociology social methodology methodological self-altering self-fulfilling self-denying prophecy belief reflexive reflexivity institution institutionalise institutionalised social construction Berger Luckmann Bhaskar critical realism Lawson Bordieu habitus field spread impact ideation ideational structure social structure action creativity creative economists sociology philosophy of science homo economicus homo oeconomicus economic man economic agent rational economic man man lucas critique Goodhart's law Keynes Marx Mill Hayek Hicks Samuelson Walras Jevons Arrow Debreu Samuelson Merton sociology of economics sociology of scientific knowledge SSK Holton prediction control reflexive prediction reflexivity Whitley Mackie canonization Henshel Grunberg Modigliani Morgenstern Lucas Muth Simon Blyth Hall Sikkink Hira Hood institutionalize institutionalized socialise socialisation internalise internalisation internalization socialization behaviour behavior Thomas theorem expectations stage model productive thinking evolution

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