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  • 1
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    Untersuchung der Photooxidantien Wasserstoffperoxid, Methylhydroperoxid und Formaldehyd in der Troposphäre der Antarktis (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: Photooxidants play an important role for the oxidation capacity of the troposphere. The presented work deals with seasonal changes of atmospheric photooxidants like hydrogen peroxide (H2O2), methylhydroperoxide (MHP) and formaldehyde (HCHO). The principal purpose was to follow and quantify the mixing-ratios of these photochemical species for the first time over a complete annual cycle in Antarctica. During two field campaigns at the German Antarctic station Neumayer (overwintering campaign from January 1997 until March 1998 and a shorter campaign from January to March 1999) continuous measurements of atmospheric mixing-ratios were performed. A continuous wet-chemical technique was used for peroxides and formaldehyde sampling and analysis. Species were quantified by fluorescence detection. In order to compare the results and measurements with well-known reaction mechanisms a photochemical box model was applied. The obtained time series show a pronounced seasonal variation with higher values during summer. For the first time atmospheric concentrations of H2O2, MHP and HCHO were documented during polar night in winter. The mixing-ratios were significantly higher than expected due to missing actinic radiation essential for photochemical production. Trajectory analyses and calculations with a three-dimensional model showed that during winter the mixing-ratios of photooxidants are mainly affected by long-range transport in the free troposphere. Investigations during the Antarctic ó́zone hole period ́́show no significant impact of the increased UV-B radiation on the photooxidants. The findings of this work contribute to a better understanding of the photochemistry of the investigated trace gases in the clean troposphere of Antarctica and provide a useful data record for further photochemical modeling.
    Description: thesis
    Keywords: 551.5 ; 551.9 ; 550 ; TYY 200 ; TVA 210 ; Antarktis {Meteorologie und Klimatologie} ; Chemische Zusammensetzung der Atmosphäre {Meteorologie}
    Language: German
    Type: monograph , publishedVersion
    Format: 176 S.
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  • 2
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    Entwicklung und Anwendung eines photochemischen schräge Säulen Modell-Paketes zur Interpretation von DOAS-Daten atmosphärischer Spurengase (2010)
    Univ. Bremen
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    Publication Date: 2021-03-29
    Description: Besides measurements of atmospheric trace gases and laboratory studies of chemical reactions, modelling has been recognised to be of increasing importance to improve our knowledge of the atmosphere and the capabilities of photochemical models. Main scope of this work was the development of a photochemical atmospheric model, which was especielly designed for the interpretation of Differential Optical Absorption measurments (DOAS). This model has been used to improve our knowledge of atmospheric chemistry. For example, for the first time it was possible to demonstrate that a significant amount of IO in a range of 0.65 to 0.8 pptv is present in the stratosphere in the polar region (Ny-Alesund,Spitzbergen). Moreover it has been shown that such amounts of stratospheric IO lead to an additional Ozone loss in the range of 10 % in cold arctic winters.
    Description: thesis
    Keywords: 551.5 ; 550 ; TUA 700 ; TVA 210 ; Verfahren zur Untersuchung der freien Atmosphäre {Meteorologie} ; Chemische Zusammensetzung der Atmosphäre {Meteorologie}
    Language: German
    Type: monograph , publishedVersion
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  • 3
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    Die Ozonverteilungen der Nordhemisphäre 1997 - 2000 gemessen mit GOME (2010)
    Univ. Bremen
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    Publication Date: 2021-03-29
    Description: Ozone profile retrieval, ERS-2, GOME, FURM, ozone decline, Northern hemisphere. - Measurements of stratospheric ozone over the Northern hemisphere forthe winter/spring periods of 1997 to 2000 taken with the GOMEinstrument were used to derive the chemical ozone depletion inside thepolar vortex. GOME onboard the ERS-2 satellite measures radiationcoming from the Earth in the UV/vis spectral range.To discern the chemical depletion from dynamical influences, a modelwas developed to calculate vortex averaged diabatic descent ratesusing the radiative transfer model MIDRAD and the FURM ozoneprofiles. The permeability of the Arctic vortex was analysed by usingthe trajectory model TANGO in conjunction with a reverse domainfilling algorithm, developed within the framework of this thesis.The chemical ozone ...
    Description: thesis
    Keywords: 551.5 ; 550 ; TUA 850 ; TVA 210 ; TY 100 ; Satellitenmeteorologie ; Chemische Zusammensetzung der Atmosphäre {Meteorologie} ; Nördliche Hemisphäre {Meteorologie und Klimatologie}
    Language: German
    Type: monograph , publishedVersion
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  • 4
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    Messungen von dynamischen Tracern und Ozon in der arktischen Stratosphäre (2010)
    Univ. Bremen
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    Publication Date: 2021-03-29
    Description: Ozone chemistry, tracer measurements, radiometry, airborne,submillimeterwave, Arctic, stratosphere. - The Airborne Submillimeter Radiometer (ASUR) is a passive heterodyne instrument using a superconducting detector with an instrumental frequency range from 604.3 to 662.3 GHz.Operating onboard an aircraft to avoid absorption by tropospheric water vapor key species of the stratospheric ozone chemistry can be detected for a vertical altitude range from 15 to 55 km. In the winter 1999/2000 the ASUR instrument participated in the THESEO 2000/SOLVE project onboard the NASA research aircraft DC-8. Three deployments were carried ...
    Description: thesis
    Keywords: 551.5 ; 550 ; TUA 800 ; TVA 210 ; TYY 100 ; Radarmeteorologie ; Chemische Zusammensetzung der Atmosphäre {Meteorologie} ; Arktis {Meteorologie und Klimatologie}
    Language: German
    Type: monograph , publishedVersion
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  • 5
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    Strahlungstransport- und Inversions-Algorithmen zur Ableitung atmosphärischer Spurengasinformationen aus Erdfernerkundungsmessungen in Nadirgeometrie im ultravioletten bis nahinfraroten Spektralbereich am Beispiel SCIAMACHY (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 551.5 ; 550 ; TUA 850 ; TUA 500 ; TVA 210 ; Satellitenmeteorologie ; Meteorologische Modelle ; Chemische Zusammensetzung der Atmosphäre {Meteorologie}
    Language: German
    Type: monograph , publishedVersion
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  • 6
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    Langfristige Variabilität der thermohalinen Zirkulation in einem gekoppelten Ozean-, Meereis-, Atmosphärenmodell (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: Thermohaline circulation, variability, energy and moisture balance model, paleoceanography. - Freshening of high latitude surface water can change the large scale oceanic transport of heat and salt. Consequently, atmospheric and sea ice perturbations over the deep water production sites excite a large scale response establishing an oceanic t̀̀eleconnection'' with time scales of years to centuries. To study these feed-backs, an atmospheric energy and moisture balance model (EMBM), predicting the heat and fresh water fluxes at the surface, and a thermodynamic sea ice model were constructed and coupled to the GFDL ocean model MOM2. The heat and moisture transports by transient eddies in the EMBM are parameterized by diffusion. The coupled model reproduces many aspects of today's oceanic circulation. The most interesting features of the coupled model are the sensitivity of the thermohaline circulation to changes in the configuration, the multidecadal variability in the ocean-sea ice system, and the behaviour of the thermohaline circulation during transitions between glacial and interglacial periods. A very strong thermohaline circulation develops in the coupled system that is not evident in the stand-alone ocean model. An interesting aspect of this behaviour is the existence of a maximum strength in the overturning. Beyond this maximum, evaporation in the subtropics cannot balance the northward salt-transport. As a result, the watermasses over the deep water production sites become fresher, leading to a collapse of the thermohaline circulation. The associated changes in the sea ice cover prevent the system to recover. ...
    Description: thesis
    Keywords: 551.6 ; 550 ; QDC 200 ; Synoptische Klimageographie ; Wärme- und Strahlungshaushalt der Atmosphäre {Meteorologie} ; Statistische Klimatologie und Klimatologische Modelle ; Klimaänderungen
    Language: German
    Type: monograph , publishedVersion
    Format: 132 S.
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  • 7
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    Data assimilation in a regional finite element sea-ice model for the Arctic (2010)
    Univ. Bremen
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    Publication Date: 2021-03-29
    Description: Sea-ice, Finite Element Sea-Ice Model, Kalman Filter, Data Assimilation. - The Arctic region is sensitive to climate change. Since the Arctic sea-ice cover influences the surface heat budget of the Earth the observed sea-ice decline is seen as an indication of global warming. Furthermore, the dynamics of sea ice plays an important role for the sea-ice mass distribution in the Arctic, for the production of dense, cold, and salty water in the Arctic Ocean, which contributes to the thermohaline circulation, and also for the freshwater budget of the Nordic Seas. Thus, a realistic description of sea-ice motion is important to draw conclusions for the mass transport and sea-ice mass distribution. The Finite-Element Sea-Ice Model simulates the large-scale physical sea-ice processes like the sea-ice growth and circulation realistically. The model domain covers the entire Arctic Ocean and its marginal seas. Together with the Singular Evolutive Interpolated Kalman (SEIK) Filter and remotely sensed sea-ice drift observations this sea-ice model is applied for data assimilation to investigate details of the sea-ice dynamics. So far, drift assimilation has been carried out to analyze and modify only the drift field with subsequent computation of the advection or redistribution of ice mass which corresponds more to the physical model behavior than a statistical analysis that the SEIK Filter provides. The sea-ice drift data assimilation with the SEIK Filter achieves drift modification and furthermore changes in the two other sea-ice variables concentration and thickness. The modifications of these "unobserved variables" (within the meaning of data assimilation) are validated and it is found that they are in good agreement for at least 2 months for the sea-ice thickness and even 4 months for the sea-ice concentration which is the longest period examined. The drift improvement is achieved due to the sea-ice concentration and ...
    Description: thesis
    Keywords: 551 ; 550 ; VAQ 990 ; VAQ 500 ; TVH 100 ; TOY 000 ; Meereis {Glaziologie} ; Gletscherbewegung und Gletscherschwankungen ; Wärme- und Strahlungshaushalt der Atmosphäre {Meteorologie} ; Energiebilanzen in der Geodynamik {Geophysik}
    Language: German
    Type: monograph , publishedVersion
    Format: 141 S.
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  • 8
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    Crustal evolution of the submarine plateaux of New Zealand and their tectonic reconstruction based on crustal balancing (2010)
    Univ. Bremen
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    Publication Date: 2021-03-29
    Description: Tectonics, marine geophysics, plate-tectonic reconstruction, new zealand, antarctica, seismic refraction/wide-angle reflection, Gondwana break-up. - The last supercontinent fell into pieces with the break-up of Gondwana. In this context, the separation of the microcontinent of New Zealand from Antarctica is a jigsaw puzzle of many pieces. Its parts lay at the convergent margin of East Gondwana, which changed into a divergent margin within a geologically short time. That is why the microcontinent of New Zealand experienced different tectonic regimes and phases of the Wilson cycle. Although it is a good object of investigation due to its changing history, remarkably little is known about the submerged parts of the microcontinent. Knowledge of the magmatic-tectonic development of the submarine plateaux such as Campbell Plateau and Chatham Rise will improve the understanding of the processes that led to the late Gondwana break-up, and, in turn, lead to better reconstructions of East Gondwana, as Zealandia is a key piece in plate-kinematic reconstructions of this part of Gondwana. The central part of this thesis deals with the separation process of Zealandia from Antarctica leading to an improved reconstruction of New Zealand with emphasis on the submarine plateaux. Bounty Trough separating Chatham Rise from Campbell Plateau, and the Great South Basin separating Campbell Plateau from the South Island are investigated with seismic refraction and reflection methods. They are interpreted jointly with magnetic and gravity data. The results of crustal thickness modelling based on satellite gravity data are combined with existing information about crustal thickness of Zealandia. With these data ...
    Description: thesis
    Keywords: 551.136 ; 550 ; TST 000 ; Ozeanien {Geophysik} ; Pazifischer Ozean {Geophysik} ; Geotektonische Entwicklung der Erdkruste {Tektonik}
    Language: German
    Type: monograph , publishedVersion
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  • 9
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    Reconstruction of oceanic currents and climate change in the Transkei Basin, South African gateway (2010)
    Univ. Bremen
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    Publication Date: 2021-03-29
    Description: Reflection seismics, sediment drifts, bottom currents. - The region south of South Africa has been a crucial gateway for large scale Thermohaline Circulations since late Eocene times. Here, three of the most important currents for maintaining the global heat exchange, namely the warm and surface related Agulhas Current (AC), and the cold and denser North Atlantic Deep Water (NADW) as well as the Atlantic Bottom Water (AABW), flow around South Africa. Due to the special tectonic and geologic situation, a huge amount of the deep and bottom water masses that flow around South Africa have to pass the narrow Agulhas Passage, located between the South African continental shelf and the submarine Agulhas Plateau. As a result, the sedimentary infill of the Transkei Basin, which is located east of the Agulhas Plateau, has been predominantly influenced by NADW and AABW activity since ~36 Ma. Via the analysis of this sedimentary infill, a palaeo current reconstruction of (proto-) NADW and (proto-) AABW revealed changing flow paths and flow strengths since then. These variations in current attributes were triggered by large scale effects, such as the opening of the Tasman Gateway and the Drake Passage in the Late Eocene, or the closure of the Isthmus of Panama in the Pliocene. A more detailed analysis of the Transkei Basin's depocentre locations and interface outlines resulted in a palaeo flow path reconstruction for this region. Moreover, palaeo climate conditions from the Late Cretaceous were partially reconstructed ...
    Description: thesis
    Keywords: 551.462 ; 551.69 ; 550 ; TSZ 100 ; Atlantischer Ozean {Geophysik}
    Language: German
    Type: monograph , publishedVersion
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  • 10
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    Deformation microstructures (2010)
    Univ. Bremen
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    Publication Date: 2021-03-29
    Description: Ice, microstructures, subgrain boundaries, recrystallization, flow, deformation. - The primary objective of this thesis is the investigation of microstructures obtained from samples from the EPICA Dronning Maud Land ice core from Antarctica. The goal is to gain understanding of deformation processes an deformation-related recrystallization mechanisms using these structures. The structures are visualized with the new microstructure mapping method using the preferred sublimation along defect regions in the crystal. This method enables observation in high resolution as well as overview over a significant sample volume. In order to provide unambiguous proof of their deformational origin and to offer interpretation and characterization, experimental reproduction of the microstructural features are performed using creep tests. Subgrain boundaries and grain-boundary morphology are identified as the most direct effects of deformation and recrystallization processes, which are still easily observable. They can be used additionally to the conventional parameters (grain size, crystal-orientation distribution) to determine these mechanisms. Different sbugrain-boundary types observed in experimentally deformed samples as well as in natural ice indicate several formation processes. Results obtained from this new and novel data suggest a profound reconsideration of the classical tripartition of recrystallization regimes described in the literature in ice sheets. Instead, dynamic recrystallization in two of its forms (rotation recrystallization and strain-induced migration recrystallization) dominates the microstructure evolution in all depth regions of the EDML ice core. Results of systematic microstructure analysis of creep-test samples demonstrate ...
    Description: thesis
    Keywords: 551.312 ; 548.842 ; 551 ; 550 ; VAE 140 ; VAQ 100 ; Gesteinsdeformation {Strukturgeologie} ; Gletscheruntersuchungen im Allgemeinen
    Language: German
    Type: monograph , publishedVersion
    Format: 129 S.
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