• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 9
  • 5
  • 2
  • 2
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 27
  • 13
  • 7
  • 7
  • 7
  • 6
  • 6
  • 5
  • 5
  • 4
  • 4
  • 4
  • 4
  • 4
  • 4
  • 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.
11

Long Term Projection of Ocean Wave Climate and Its Climatic Factors / 気候変動に伴う波浪変化の長期予測と気候因子解析

Shimura, Tomoya 23 March 2015 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第18931号 / 工博第3973号 / 新制||工||1612(附属図書館) / 31882 / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 間瀬 肇, 教授 平石 哲也, 准教授 森 信人 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM
12

Integrated Remote Sensing and Forecasting of Regional Terrestrial Precipitation with Global Nonlinear and Nonstationary Teleconnection Signals Using Wavelet Analysis

Mullon, Lee 01 January 2014 (has links)
Global sea surface temperature (SST) anomalies have a demonstrable effect on terrestrial climate dynamics throughout the continental U.S. SST variations have been correlated with greenness (vegetation densities) and precipitation via ocean-atmospheric interactions known as climate teleconnections. Prior research has demonstrated that teleconnections can be used for climate prediction across a wide region at sub-continental scales. Yet these studies tend to have large uncertainties in estimates by utilizing simple linear analyses to examine chaotic teleconnection relationships. Still, non-stationary signals exist, making teleconnection identification difficult at the local scale. Part 1 of this research establishes short-term (10-year), linear and non-stationary teleconnection signals between SST at the North Atlantic and North Pacific oceans and terrestrial responses of greenness and precipitation along multiple pristine sites in the northeastern U.S., including (1) White Mountain National Forest - Pemigewasset Wilderness, (2) Green Mountain National Forest - Lye Brook Wilderness and (3) Adirondack State Park - Siamese Ponds Wilderness. Each site was selected to avoid anthropogenic influences that may otherwise mask climate teleconnection signals. Lagged pixel-wise linear teleconnection patterns across anomalous datasets found significant correlation regions between SST and the terrestrial sites. Non-stationary signals also exhibit salient co-variations at biennial and triennial frequencies between terrestrial responses and SST anomalies across oceanic regions in agreement with the El Nino Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO) signals. Multiple regression analysis of the combined ocean indices explained up to 50% of the greenness and 42% of the precipitation in the study sites. The identified short-term teleconnection signals improve the understanding and projection of climate change impacts at local scales, as well as harness the interannual periodicity information for future climate projections. Part 2 of this research paper builds upon the earlier short-term study by exploring a long-term (30-year) teleconnection signal investigation between SST at the North Atlantic and Pacific oceans and the precipitation within Adirondack State Park in upstate New York. Non-traditional teleconnection signals are identified using wavelet decomposition and teleconnection mapping specific to the Adirondack region. Unique SST indices are extracted and used as input variables in an artificial neural network (ANN) prediction model. The results show the importance of considering non-leading teleconnection patterns as well as the known teleconnection patterns. Additionally, the effects of the Pacific Ocean SST or the Atlantic Ocean SST on terrestrial precipitation in the study region were compared with each other to deepen the insight of sea-land interactions. Results demonstrate reasonable prediction skill at forecasting precipitation trends with a lead time of one month, with r values of 0.6. The results are compared against a statistical downscaling approach using the HadCM3 global circulation model output data and the SDSM statistical downscaling software, which demonstrate less predictive skill at forecasting precipitation within the Adirondacks.
13

INVESTIGATION OF THE RELATIONSHIP BETWEEN THE PACIFIC/NORTH AMERICAN (PNA) AND NORTH ATLANTIC OSCILLATION (NAO) TELECONNECTIONS, AND GREAT LAKE-EFFECT SNOWFALL

Cripe, Douglas G. 30 November 2005 (has links)
No description available.
14

Large-scale moisture flux analysis for the United States

Wang, Sheng-Hung 03 February 2004 (has links)
No description available.
15

El Niño Southern Oscillation teleconnections and their effects on the Amundsen Sea region

Yiu, Yu Yeung Scott January 2018 (has links)
El Niño Southern Oscillation events have global implications both climatologically and socio-economically. One such climatological teleconnection is manifested in the Amundsen Sea region (ASR). The Amundsen sea low (ASL) is the dominant low pressure system located around the ASR and is important to the climate of Western Antarctica. Therefore, it is important to understand the ASL and any phenomena that may affect it. This thesis focuses on the ENSO--ASR teleconnection under El Niño conditions and the mechanism behind it. The ENSO--ASR teleconnection was explored using the UM version 8.4 (HadGEM3) model. Time--slice experiments with various magnitudes of idealised perpetual ENSO events are imposed. Two sets of `switch on' experiments in which tropical Pacific SSTs were ramped up were also carried out to investigate the transient nature of the teleconnection. The seasonality of the ENSO--ASR teleconnection is known from previous studies to be stronger in winter compared to summer. The mechanism behind the seasonality was explored using the time--slice experiments. The seasonality is found to originate from the seasonal differences in the Southern Hemispheric jets. As the subtropical jet is only present in austral winter, Rossby wave source anomalies can only be generated in the mid--latitudes in winter. Furthermore, the propagation of the Rossby waves is not possible in summer due to the strong polar front jet. The lack of the source and propagation in summer explains the weaker ENSO--ASR teleconnection. A flowchart summarising the mechanism was created and then verified by the transient runs. The linearity of the ENSO--ASR teleconnection within El Niño has not been previously investigated. This is mainly due to insufficient reanalysis data available to overcome the high internal variability in the ASR. In this thesis, the linearity of the teleconnection under El Niño is studied using the time--slice runs. The results indicate linearity (within errorbars) for both the summer and winter seasons up to historically maximum El Niños. However, under extreme El Niños (beyond historic records) in winter, the teleconnection is no longer linear. The UPSCALE dataset was used to investigate the effects of horizontal resolution on the simulation of the ASL climatological state and the ENSO--ASR teleconnection. The UPSCALE dataset consists of ensembles of HadGEM3 simulations at three different horizontal resolutions. The high resolution model was found to better simulate the ASL while the low resolution model was found to better simulate the ENSO--ASR teleconnection.
16

Relationship between tropical Atlantic Sea surface temperature variability and southern Indian Ocean tropical cyclones

DeBlander, Evan F. 01 May 2012 (has links)
Recent studies have found that equatorial Atlantic sea surface temperature (SST) variability may be influencing tropical Indian Ocean climate (Kucharski 2009, Wang 2009). Due to the economic and social impact of tropical cyclones, it is important to investigate how an Atlantic-Indian Ocean connection may be affecting tropical cyclone behavior in the southern Indian Ocean. In this study, the International Best Track Archive for Climate Stewardship (IBTrAC) tropical cyclone database is used to derive metrics of tropical cyclone behavior, which are then compared with indices of tropical Atlantic SST variability representing Atlantic Niño, and Benguela Niño events. Changes in tropical Atlantic SSTs are found to coincide with significant differences in tropical cyclone activity for portions of the southern Indian Ocean. In addition, for these same regions, tropical Atlantic SST variability is associated with changes in large-scale atmospheric conditions, including steering flow, low level vorticity, and humidity, typically associated with tropical cyclogenesis, and tropical cyclone track. The changes in steering flow related to both indices of Atlantic SST anomaly are reproduced by an atmospheric model. The changes in steering flow are also found to be linked to changes in TC translational velocity, and TC tracking. These findings indicate a possible link between tropical Atlantic conditions and cyclone activity in the Indian Ocean mediated through a teleconnection between tropical Atlantic SSTs and large scale atmospheric conditions over the southern Indian Ocean. The teleconnection related to the Benguela Niño region of SST variability was found to consist of a Rossby wave initiated off the coast of South America, and propagating into the Indian Ocean, thereby influencing several atmospheric variables, including steering flow. The teleconnection related to the Atlantic Niño region of SST variability was not well defined, although there was some evidence of a Walker circulation anomaly extending from the equatorial Atlantic over the continent of Africa, and influencing SIO steering flow. / Graduation date: 2012
17

高速公路對都市土地遠距連接的影響 / The impact of highway on Urban Land Teleconnection

李朝誌, Lee, Chao Chih Unknown Date (has links)
都市土地遠距連接概念在國際間提出,核心概念為一地之土地使用變遷可能來自於遠距地區之影響,與過去認為土地使用變遷係受周遭地區之影響有所差異。國際上探討其相關主題的文章有日漸增加的趨勢,且多數文章皆提到交通設施於都市土地遠距連接扮演重要角色。然而目前對於都市土地遠距連接多處於概念性探討階段,國內外並未曾出現實證研究來對此概念進行驗證,因此本研究嘗試從交通與土地使用的概念切入,針對都市土地遠距連接進行實證分析。 本研究選擇台灣本島地區349個鄉鎮市區作為研究對象,應用多階層線性模型(Hierarchical Linear Modeling, HLM)分析民國95年至105間高速公路與都市土地遠距連接的關係。模型變數包含建成地面積變化、可及性相關指標及吸引力相關指標。 實證模型顯示,高速公路興建增加之可及性與都市土地遠距連接間呈現負向關係,但其係數趨近於0,表示影響極小,而地方吸引力與都市土地遠距連接間呈現正向關係,且係數大於0。根據模型得到以下結論,高速公路的興建對於都市土地遠距連接之影響程度有限,而地方吸引力對於都市土地遠距連接具有較大的影響。 / The concept of urban land teleconnection has been proposed internationally, and the core concept is that land use change may come from the impact of remote areas, which is different from the existing theory that land use change results from the influence of surrounding areas. There is an increasing amount of articles talking about urban land teleconnection in recent years and most of these articles refer to the important role of transport facilities in urban land teleconnection. However, at present, there are no empirical studies to verify the urban land teleconnection. Therefore, the purpose of this paper is to conduct an empirical research to analyze the urban land teleconnection from the transportation and land use point of view. In this study, hierarchical linear modeling (HLM), which uses the dataset collected in Taiwan’s 349 townships from 2006 to 2016, is applied to analyze the relationship between the highway and urban land teleconnection. In hierarchical linear modeling, the variables include the variation of the built environment, the variation of accessibility caused by the highway construction and the attraction factors. The empirical model shows that the variation of accessibility caused by the highway construction has a negative relationship with the urban land teleconnection, but the influence is negligible. Nevertheless, there is an obvious positive relationship between the attraction factors and the urban land teleconnection. According to the model, the construction of highways has a limited influence on the urban land teleconnection, but the attraction factors have a great influence on the urban land teleconnection.
18

Characterization of Holocene climate variability in the west of Europe and Mediterranean basin using high-resolution stalagmite records / Caractérisation de la variabilité du climat holocène à l’ouest de l’Europe et du bassin de la Méditerranée à partir de l’étude haute résolution de spéléothèmes

Ruan, Jiaoyang 16 September 2016 (has links)
Déchiffrer le climat de l’Holocène est la base d’une meilleure compréhension du climat moderne. En effet, à cette époque le climat en Europe est très complexe est montre de fortes variations spatiales et il reste beaucoup à faire pour améliorer la couverture géographique d’enregistrements bien datés et de haute résolution. En tant qu’archives paléoclimatiques, les spéléothèmes ont de larges avantages concernant leur chronologie et leur résolution temporelle et peuvent aider à combler cette lacune. Dans cette thèse, des stalagmites holocènes ont été sélectionnées selon un transect N-S entre les latitudes 35° et 65°N à l’ouest de l’Europe et du bassin méditerranéen (de la Suède à l’Algérie). Elles ont été datées densément par U-Th et échantillonnées à haute résolution pour analyser leur composition isotopique et géochimique. Le climat de l’Holocène a été déduit des analyses isotopiques de la calcite (δ¹³C, δ¹⁸O) et du rapport Mg/Ca. Combinées avec les données existantes et avec les simulations numériques des modèles, ces nouvelles données ont permis d’émettre des hypothèses sur les processus dynamiques contrôlant les changement climatiques régionaux comme les divers modes impliqués dans la circulation océanique et atmosphérique. Sur un site archéologique particulier, le lien climat/activités humaines a aussi pu être étudié. Les principaux résultats de cette thèse sont : 1) les enregistrements en δ¹⁸O, δ¹³C et Mg/Ca d’une stalagmite de la grotte de Villars (sud-ouest de la France), ont révélé une variabilité décennale à multimillénaire du climat au cours des derniers 14200 ans ainsi que les preuves d’une déforestation il y a environ 1000 ans ; 2) deux stalagmites provenant de la grotte de Villars au sud-ouest de la France et de la grotte Korallgrottan au nord-ouest de la Suède ont enregistré de façon remarquable l’événement climatique du 8.2 ka et les différentes étapes qui le composent montrant des différences régionales de température et d’humidité entre les deux sites. Celles-ci sont associées avec une interruption suivie d’une réorganisation de la circulation océanique et atmosphérique ; 3) les enregistrements en δ¹⁸O et en δ¹³C de deux stalagmites de la grotte de Villars suggèrent aussi l’existence d’une période humide multi-centennale il y a ~7200-7600 liée éventuellement à la fonte de la dernière portion de la calotte de la Laurentide ; 4) les isotopes stables (δ¹⁸O, δ¹³C) d’une stalagmite de la grotte du Père-Noël située au sud-est de la Belgique, révèle de larges variations hydro climatiques entre 10500 et 4200 ans. En particulier, une période sèche multi-centennale est mise en évidence il y a ~5600-6000 ans probablement liée à un changement des vents d’ouest ; 5) au nord de l’Algérie, dans la grotte de Gueldaman, plusieurs stalagmites ont montré, par leur δ¹³C et leur δ¹⁸O, l’impact d’une période sèche sur l’occupation humaine et finalement l’abandon du site par les hommes préhistoriques il y a ~4200 ans. / Deciphering Holocene climate is the basis to understand modern climate change. The Holocene climate of Europe is highly complex and shows large spatial differences; much is to be done to improve the spatial coverage of well-dated, high resolution climate records. Stalagmite as paleoclimate archive has large advantages in its chronology and their temporal resolution and thus can help in answering this question. In this thesis, stalagmites were collected, broadly along a meridional transect from 35 to 65°N, in the west of Europe and Mediterranean basin (from Sweden to Algeria). They were densely dated by the U-Th method and their isotopic and geochemical compositions were analyzed at high spatial resolutions. The Holocene climate was inferred from the stalagmite δ¹³C, δ¹⁸ and Mg/Ca time series. Combining with existent data and model simulations the collected new data was used to understand dynamic processes involved in driving regional change, such as varying modes of ocean and atmospheric circulation. Uniquely, the possible links between the changes of past climate conditions and human activities at an archeological site were examined, too. The main results of this thesis are summarized as: (1) The δ¹⁸O, δ¹³C and Mg/Ca records of a stalagmite from Villars Cave, Southwestern France document a series of decadal to multi-millennial climatic variations over the last 14200 years as well as deforestation ~1000 years ago; (2) The precisely-dated, sub-decadal δ¹⁸O, δ¹³C and Mg/Ca records of stalagmites from Villars Cave, SW-France, and Korallgrottan Cave, NW-Sweden, reveal multiple stage climatic variations in relation to the 8200 year event. Reconstructed variations in both temperature and humidity exhibit different patterns at the two sites, respectively, in the south and north of Europe, which can be associated with the interruption and reorganization of ocean-atmospheric circulation; (3) The δ¹⁸O and δ¹³C records of two stalagmites from Villars Cave suggest multi-century wetness ~7200-7600 years ago which possibly linked to the demise of last portion of Laurentide Ice Sheet; (4) The δ¹⁸O and δ¹³C records of a stalagmite from Pere Noël Cave, Southeastern Belgium reveal large decadal to millennial hydroclimate variations between 10500 and 4200 years ago. Particularly, multi-century enhanced aridity occurred ~5600-6000 years ago which probably had attributed to the changes in regional atmospheric circulation and the westerly jet; (5) The δ¹³C and δ¹⁸O records of two Mid-Holocene stalagmites from Gueldaman GLD1 Cave, Northern Algeria provide evidence of a prolonged drought ~4200 years ago in Western Mediterranean basin. The drought coincides with, and therefore may have contributed to, an abandonment of ancient human occupation of the cave.
19

Associação da variabilidade climática dos oceanos com a vazão de rios da Região Norte do Brasil / Association of climatic variability of the oceans with the outflow of rivers in Northern Brazil

Silva, Elaine Rosangela Leutwiler di Giacomo 17 May 2013 (has links)
O objetivo desta pesquisa foi investigar a relação linear existente entre a Temperatura de Superfície do Mar (TSM) dos oceanos Pacífico e Atlântico e a vazão do rio Madeira, localizado na parte sul da região Norte do Brasil. A investigação foi feita nas escalas mensal, sazonal e anual, para o período de 1968 a 2009. A hipótese de que alterações climáticas na região Norte do Brasil estariam associadas a episódios de aquecimento e resfriamento dos oceanos globais, já que quando ocorrem têm o potencial de modificar o padrão de precipitação em áreas remotas do globo, foi a motivação central da pesquisa. A pesquisa foi desenvolvida com base em análises estatísticas para os dados de TSM, índices climáticos e a vazão do rio Madeira. Observou-se que a vazão mensal do rio Madeira apresenta correlação linear significativa com áreas específicas dos oceanos Atlântico e Pacífico. No Oceano Atlântico Norte, são significativas as correlações obtidas nos setores tropical (área AT3) e norte (área AT1). O setor subtropical do Atlântico Norte (AT2) apresenta correlações lineares não tão expressivas como suas áreas tropical e norte. O Atlântico Sul não apresenta áreas com correlações lineares significativas com a vazão. As áreas com correlação significativa do Atlântico Norte (AT1) apresentam valores negativos máximos entre -0,6 e -0,4. Os valores de correlação linear entre a vazão mensal do rio Madeira e a TSM do Atlântico (AT2) apresentam um pequeno aumento para os cálculos realizados com defasagem temporal de até nove meses, entre 0,3 a 0,4 para 5 meses de defasagem entre a vazão e a TSM. A TSM do setor oeste do Pacífico tropical apresenta fortes valores negativos de correlação linear com a vazão do rio Madeira, com valores máximos que variam entre -0,7 e -0,4. Tal qual acontece para o Atlântico, as águas superficiais do Pacífico tropical oeste apresentam um pequeno aumento dos valores de correlação linear para defasagens maiores entre a TSM e a vazão. As áreas com forte correlação negativa no setor oeste do Pacífico tropical foram denominadas PA1, no norte, e PA3, no sul. Uma pequena área com correlação significativa e positiva a leste da bacia do Pacífico, junto à costa do Chile, foi denominada PA2. Nesta área os valores máximos de correlação linear entre a vazão mensal e a TSM variam entre 0,2 e 0,4. A análise de correlação linear entre a vazão anual do rio Madeira e índices climáticos indicam que os índices ODP, MEI e OAN são os mais bem correlacionados com a vazão, apresentando valores iguais a 0,89, 0,86 e 0,85, respectivamente. Com base na TSM das áreas bem correlacionadas com a vazão do rio Madeira e nos índices climáticos considerados, foi desenvolvido um modelo estocástico de regressão linear múltipla para a previsão da vazão trimestral com antecedência de um trimestre. A TSM das áreas do setor oeste do Pacífico tropical, PA1, e do Atlântico Norte tropical, AT3, constituíram as variáveis selecionadas para a elaboração do modelo estocástico. O modelo estocástico foi desenvolvido para o início da série temporal considerada, de 1968 a 1988, e apresentou um ajuste linear com coeficiente de determinação igual a 78%. A verificação do modelo foi feita para o final da série, de 1989 a 2009. O erro médio normalizado calculado pela diferença entre os valores de vazão previstos pelo modelo e os observados foi igual a 40%. Desta forma, conclui-se que a vazão trimestral do setor sul da região Norte do Brasil é uma variável que pode ser prevista com base na variabilidade da temperatura das águas superficiais dos oceanos Pacífico e Atlântico. A análise do comportamento atmosférico com base em períodos específicos de anomalias de TSM no Atlântico Norte tropical indica que a ocorrência de TSMs mais altas (baixas) que o normal foram acompanhadas por ventos de leste mais fracos (fortes). Foram analisados os campos atmosféricos médios para os meses chuvosos de novembro a março para as variáveis Velocidade Vertical (Omega) em 500 e 850 hPa, divergência e vorticidade do vento. Os resultados obtidos demonstram que em média, a variabilidade atmosférica foi determinante no que se refere às anomalias apresentadas pela vazão. / The objective of this research was to investigate the linear relation between the sea surface temperature (SST) over Pacific and Atlantic oceans and the outflow of the Madeira river, located at the southern part of the Northern region of Brazil. The investigation considered monthly, seasonal and annual scales, to the period between 1968 to 2009. The consideration about the influence of heating and cooling of oceanic areas over climate around the world constitutes the main hypothesis taken in account in the study. The research was developed based on statistical analysis considering SST, climatic indexes and river outflow data. The monthly outflow for Madeira River shows significant linear correlation to SST at specific areas over Atlantic and Pacific. Over North Atlantic, the linear correlation values are significant at the tropical and north sectors, namely AT3 and AT1, respectively. The subtropical sector of North Atlantic presents positive correlation but not too expressive as the tropical and north areas of Atlantic. South Atlantic does not present significant values of linear correlation with the river outflow. The area with significant correlation over North Atlantic (AT1) presents maximum negative values ranging between -0,6 and -0,4. In general, the greater the interval between river outflow and SST data, greater is the linear correlation values. SST data from the western sector of tropical Pacific presents strong negative correlation with Madeira River outflow data, and shows maximum values ranging between -0,7 and -0,4. The areas to the West of Pacific showing high negative correlation were named PA1 and PA3, to northern and southern sectors, respectively. A small area that shows significant positive linear correlation to the river outflow data, PA2, is located over the eastern side of Pacific basin, very closed to the coast of Chile. In this area, the linear maximum correlation values range between 0,2 and 0,4. Linear correlation analysis between annual river outflow data and climatic indices indicates that PDO, MEI and NAO are those more correlated with the river outflow data, presenting values equal to 0,89, 0,86 e 0,85, respectively. Based on averaged SST and climatic indices well correlated to the Madeira River outflow data, a stochastic model was developed in order to forecast the river outflow in seasonal scale. SST from west of tropical Pacific, PA1, and from tropical North Atlantic, AT3, were selected to build up the stochastic model. The stochastic model was developed considering the first half of the total series, between 1968 and 1988, while the last period was used to validate the model, between 1989 and 2009. The linear adjusting over the first period reach a determining coefficient equal to 78% and the normalized mean error obtained for the second period was equal to 40%. Thus, we conclude that the seasonal outflow for Madeira River is a climatic variable that can be forecast based on the SST variability over specific areas on Pacific and Atlantic oceans. The analysis of atmospheric behavior based on specific periods of SST anomalies in the tropical North Atlantic indicates that the occurrence of SSTs higher (lower) than normal was accompanied by easterly winds weak (strong). We analyzed the average atmospheric fields for the rainy months from November to March for variables Vertical Speed (Omega) at 500 and 850 hPa, divergence and vorticity of the wind. The results show that approximately the atmospheric variability was decisive with regard to the deficiencies presented by the ouflow.
20

Untersuchungen zur dynamischen Kopplung der Troposphäre und der Stratosphäre / Analyses of the dynamical coupling of the troposphere and the stratosphere

Kleppek, Sabine January 2005 (has links)
Im Rahmen dieser Arbeit wurde ein besseres Verständnis der Kopplung der Troposphäre und der Stratosphäre in den mittleren und polaren Breiten der Nordhemisphäre (NH) auf Monatszeitskalen erzielt, die auf die Ausbreitung von quasi-stationären Wellen zurückzuführen ist. Der Schwerpunkt lag dabei auf den dynamisch aktiven Wintermonaten, welche die grösste Variabilität aufweisen. Die troposphärische Variabilität wird zum Grossteil durch bevorzugte Zirkulationsstrukturen, den Telekonnexionsmustern, bestimmt. Mittels einer rotierten EOF-Analyse der geopotenziellen Höhe in 500 hPa wurden die wichtigsten regionalen troposphärischen Telekonnexionsmuster der Nordhemisphäre berechnet. Diese lassen sich drei grossen geografischen Regionen zuordnen; dem nordatlantisch-europäischen Raum, Eurasien und dem pazifisch-nordamerikanischen Raum. <br><br> Da es sich um die stärksten troposphärischen Variabilitätsmuster handelt, wurden sie als grundlegende troposphärische Grössen herangezogen, um dynamische Zusammenhänge zwischen der troposphärischen und der stratosphärischen Zirkulation zu untersuchen. Dabei wurde anhand von instantanen und zeitverzögerten Korrelationsanalysen der troposphärischen Muster mit stratosphärischen Variablen erstmalig gezeigt, dass unterschiedliche regionale troposphärische Telekonnexionsmuster unterschiedliche Auswirkungen auf die stratosphärische Zirkulation haben. Es ergaben sich für die pazifisch-nordamerikanischen Muster signifikante instantane Korrelationen mit quasi-barotropen Musterstrukturen und für die nordatlantisch-europäischen Muster zonalsymmetrische Ringstrukturen ab 1978 mit signifikanten Korrelationswerten über tropischen und subtropischen Breiten und inversen Korrelationswerten über polaren Gebieten. <br><br> Bei einer Untersuchung des Einflusses der stratosphärischen Variabilität wurde gezeigt, dass sich die stärkste Kopplung von nordatlantisch-europäischen Telekonnexionsmustern mit der stratosphärischen Zirkulation bei einem in Richtung Europa verschobenen Polarwirbel ergibt, wodurch die signifikanten Korrelationen ab 1978 erklärt werden können. Eine zonal gemittelte und vor allem lokale Untersuchung der Wellenausbreitungsbedingungen während dieser stratosphärischen Situation zeigt, dass es zu schwächeren Windgeschwindigkeiten in der Stratosphäre im Bereich von Nordamerika und des westlichen Nordatlantiks kommt und sich dadurch die Wellenausbreitungsbedingungen in diesem geografischen Bereich für planetare Wellen verbessern. Durch die stärkere Wellenausbreitung kommt es zu einer stärkeren Wechselwirkung mit dem Polarjet, wobei dieser abgebremst wird. Diese Abbremsung führt zu einer Verstärkung der meridionalen Residualzirkulation. D. h., wenn es zu einer verstärkten Wellenanregung im Nordatlantik und über Europa kommt, ist die Reaktion der Residualzirkulation bei einem nach Europa verschobenem Polarwirbel besonders stark. <br><br> Die quasi-barotropen Korrelationsstrukturen, die sich bei den pazifisch-nordamerikanischen Mustern zeigen, weisen aufgrund von abnehmenden Störungsamplituden mit zunehmender Höhe, keiner Westwärtsneigung und einem negativen Brechungsindex im Pazifik auf verschwindende Wellen hin, die als Lösung der Wellengleichung bei negativem Brechungsindex auftreten. Dies wird durch den Polarjet, der im Bereich des Pazifiks stets sehr weit in Richtung Norden verlagert ist, verursacht. <br><br> Abschliessend wurde in dieser Arbeit untersucht, ob die gefundenen Zusammenhänge von nordatlantisch-europäischen Telekonnexionsmustern mit der stratosphärischen Zirkulation auch von einem Atmosphärenmodell wiedergegeben werden können. Dazu wurde ein transienter 40-Jahre-Klimalauf des ECHAM4.L39(DLR)/CHEM Modells mit möglichst realistischen Antrieben erstmalig auf die Kopplung der Troposphäre und der Stratosphäre analysiert. Dabei konnten sowohl die troposphärischen, als auch die stratosphärischen Variabilitätsmuster vom Modell simuliert werden. Allerdings zeigen sich in den stratosphärischen Mustern Phasenverschiebungen in den Wellenzahl-1-Strukturen und ihre Zeitreihen weisen keinen signifikanten Trend ab 1978 auf. Die Kopplung der nordatlantisch-europäischen Telekonnexionsmuster mit der stratosphärischen Zirkulation zeigt eine wesentlich schwächere Reaktion der meridionalen Residualzirkulation. Somit stellte sich heraus, dass insbesondere die stratosphärische Zirkulation im Modell starke Diskrepanzen zu den Beobachtungen zeigt, die wiederum Einfluss auf die Wellenausbreitungsbedingungen haben. Es wird damit deutlich, dass für eine richtige Wiedergabe der Wellenausbreitung und somit der Kopplung der Troposphäre und Stratosphäre die stratosphärische Zirkulation eine wichtige Rolle spielt. / Within the scope of this study a better understanding of the coupling of the troposphere and the stratosphere in the middle and polar latitudes (NH) on monthly timescales, caused by the propagation of quasi-stationary waves is improved. The approach was focused on the dynamical active winter months, including the largest variablity. <br><br> The tropospheric variability is strongly affected by preferred circulation patterns, the so called teleconnection patterns. The most important, regional, tropospheric teleconnection patterns in the Northern Hemisphere are determined by means of a rotated EOF-Analyses of the geopotential height at the 500 hPa level. They can be attributed to three geographical regions; North Atlantic/Europe, Eurasia and Pacific/North America. These strongest tropospheric variability patterns are taken as the basic tropospheric quantities to analyse the connections between the tropospheric and stratospheric circulation. By means of instantaneous and time-lagged correlation analyses, it has been shown for the first time that different regional, tropospheric teleconnection patterns have different effects on the stratospheric circulation. The Pacific/North American patterns reveal significant correlation values with quasi-barotropic structures and the North Atlantic/European patterns show significant correlations over tropical and subtropical latitudes and invers correlation values over the polar region. <br><br> The investigation of the stratospheric variability influence reveals that the strongest coupling of the North Atlantic/European teleconnection patterns with the stratospheric circulation appears during periods with a shift of the polar vortex towards Europe. The zonal averaged and particularly the local analyses of the wave propagation conditions show that weaker wind speed in the stratosphere over North America and the western part of the North Atlantic leads to improved wave propagation conditions in this geographical region. The stronger wave propagation produces a stronger interaction of the waves with the polar jet which results in enhanced wave breaking and an amplification of the residual circulation. In the case of a stronger wave forcing in the North Atlantic and over Europe these will be a stronger reaction of the residual circulation. The quasi-barotropic correlation structures, induced by the Pacific/North American patterns, are an indicator for evanescent waves because of the decreasing perturbations with increasing height, none westward declination and a negative refractive index in the Pacific. This is generated by the polar jet in the Pacific which is always shifted very far to the north. <br><br> Concluding, it was studied, whether Atmospheric General Circulation Models (AGCMs) can reproduce the detected connections of the North Atlantic/European teleconnection patterns with the stratospheric circulation. Therefore the transient model run of the interactively coupled chemistry-climate model ECHAM4.L39(DLR)/ CHEM is used for analysing the troposphere-stratosphere coupling, covering the period from 1960 to 1999. Both, the tropospheric and the stratospheric variability patterns have been simulated by the model. However the stratospheric patterns show a phase shift in the wave number 1 patterns and the time series of the wave number 1 structures do not offer a significant trend since 1978. The coupling of the North Atlantic/European teleconnection patterns with the stratospheric circulation shows a significantly weaker annular-like correlation structure. It turned out, that the stratospheric circulation particularly shows strong discrepancies to the observations which can influence the wave propagation conditions again. Therefore, the stratospheric circulation plays an important role for an accurate reproduction of the wave propagation and consequently for the coupling of the troposphere and the stratosphere.

Page generated in 0.1148 seconds