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Das Jahr 1816 ist in die Klimatologie als das "Jahr ohne Sommer" eingegangen. Der 1815 erfolgte Ausbruch des Vulkans Tambora auf der indonesischen Insel Sumbawa führte im darauffolgenden Jahr in vielen Teilen der Welt zu katastrophalen Missernten. Während in Nordamerika daran besonders die außerordentlich tiefen Sommertemperaturen Schuld waren, scheinen in Europa dafür sowohl die unter dem Durchschnitt liegenden Temperaturen wie auch die überdurchschnittlichen Regenmengen verantwortlich zu sein. Zeitgenössische Berichte wie auch Niederschlags- und Pegelaufzeichnungen aus verschiedenen Teilen Europas belegen eine besonders hohe Niederschlagstätigkeit im "Erntemonat" Juli des Jahres 1816 und eine hohe Wasserführung der großen europäischen Ströme in den Jahren 1816 und 1817. / The year 1816 is known in climatology as the "Year without Summer". The eruption of the Tambora volcano on the Indonesian island Sumbawa in 1815 led to catastrophic crop failures over many parts of the world in the following year. Whereas in North America those failures originated from extraordinarily low summer temperatures, causes in Europe seem to have been below-normal temperatures as well as above-normal rainfall. Contemporary reports and also precipitation and river gauge measurements from different parts of Europe document enhanced precipitation in July 1816 ("Erntemonat") and high discharges of large European rivers in years 1816 and 1817.

Abstract Major water soluble ions (Cl-, NO3-, SO42-, CH3SO3-, Na+, K+, NH4+, Mg2+, Ca2+) were determined and the results interpreted from a 121 m long ice core drilled at the summit of the Lomonosovfonna dome, Svalbard. The core covers about the past 800 years. The reliability of anion chemistry for paleoenvironmental studies, and various insoluble particles were also investigated. The ice core studied in this Thesis is the first relatively deep ice core from the central Svalbard that has been analyzed and the results interpreted and published at high resolution for all major ions. One of the clearest features of the ion profiles is anthropogenic impact. SO42- and NO3- concentrations show significant increases by the mid-20th century with slight increases already at the end of the 19th century. In addition excess Cl- and NH4+ from anthropogenic sources are detected arriving after the mid-20th century. Anthropogenically derived SO42- and NO3- have different sources on Lomonosovfonna. NO3- is correlated with NH4+ and requires interpretation in terms of both natural and anthropogenic NH4NO3 sources. The ice core ionic load consists mostly of sea salt ions (Na+, Cl-, K+ and Mg2+). Water soluble Ca2+ are mostly terrestrial in origin. Ion balance together with the Na+/Cl- ratio shows considerable change about 1730 that is most probably due to Na2CO3 input to the ice cap before 1730. Marine biogenic CH3SO3- concentrations are high and stable during the Little Ice Age. CH3SO3- concentrations show a clear change in concentrations in 1920, that is the end of the Little Ice Age in Svalbard. Regardless of anthropogenic impact, marine biogenic SO42- is appreciable in total SO42- budget even in the 20th century. The Laki volcanic eruption in Iceland in 1783 is identified in the ice core as a volcanic tephra layer and high SO42- concentration and acidity peaks. These show that SO42- arrived to the Lomonosovfonna ice cap 6–12 months later than insoluble tephra and the SO42- aerosol caused a drop in temperature. The reliability of ice core ion chemistry analyses was estimated – for the first time in an ice core using two different analytical procedures on 500 adjacent samples from the same depth. Small-scale inhomogeneity in ion concentrations shows that information from ice core layers is representative of the regional environmental and suitable for paleoclimate studies.

abstract: Assessments for the threats posed by volcanic eruptions rely in large part on the accurate prediction of volcanic plume motion over time. That predictive capacity is currently hindered by a limited understanding of volcanic plume dynamics. While eruption rate is considered a dominant control on volcanic plume dynamics, the effects of variable eruption rates on plume rise and evolution are not well understood. To address this aspect of plume dynamics, I conducted an experimental investigation wherein I quantified the relationship between laboratory jet development and highly-variable discharge rates under conditions analogous to those which may prevail in unsteady, short-lived explosive eruptions. I created turbulent jets in the laboratory by releasing pressurized water into a tank of still water. I then measured the resultant jet growth over time using simple video images and particle image velocimetry (PIV). I investigated jet behavior over a range of jet Reynolds numbers which overlaps with estimates of Reynolds numbers for short-duration volcanic plumes. By analysis of the jet boundary and velocity field evolution, I discovered a direct relationship between changes in vent conditions and jet evolution. Jet behavior evolved through a sequence of three stages - jet-like, transitional, and puff-like - that correlate with three main injection phases - acceleration, deceleration and off. While the source was off, jets were characterized by relatively constant internal velocity distributions and flow propagation followed that of a classical puff. However, while the source was on, the flow properties - both in the flows themselves and in the induced ambient flow - changed abruptly with changes at the source. On the basis of my findings for unsteady laboratory jets, I conclude that variable eruption rates with characteristic time scales close to eruption duration have first-order control over volcanic plume evolution. Prior to my study, the significance of this variation was largely uncharacterized as the volcanology community predominately uses steady eruption models for interpretation and prediction of activity. My results suggest that unsteady models are necessary to accurately interpret behavior and assess threats from unsteady, short-lived eruptions. / Dissertation/Thesis / Ph.D. Geological Sciences 2012

Das Jahr 1816 ist in die Klimatologie als das 'Jahr ohne Sommer' eingegangen. Der 1815 erfolgte Ausbruch des Vulkans Tambora auf der indonesischen Insel Sumbawa führte im darauffolgenden Jahr in vielen Teilen der Welt zu katastrophalen Missernten. Während in Nordamerika daran besonders die außerordentlich tiefen Sommertemperaturen Schuld waren, scheinen in Europa dafür sowohl die unter dem Durchschnitt liegenden Temperaturen wie auch die überdurchschnittlichen Regenmengen verantwortlich zu sein. Zeitgenössische Berichte wie auch Niederschlags- und Pegelaufzeichnungen aus verschiedenen Teilen Europas belegen eine besonders hohe Niederschlagstätigkeit im 'Erntemonat' Juli des Jahres 1816 und eine hohe Wasserführung der großen europäischen Ströme in den Jahren 1816 und 1817. / The year 1816 is known in climatology as the 'Year without Summer'. The eruption of the Tambora volcano on the Indonesian island Sumbawa in 1815 led to catastrophic crop failures over many parts of the world in the following year. Whereas in North America those failures originated from extraordinarily low summer temperatures, causes in Europe seem to have been below-normal temperatures as well as above-normal rainfall. Contemporary reports and also precipitation and river gauge measurements from different parts of Europe document enhanced precipitation in July 1816 ('Erntemonat') and high discharges of large European rivers in years 1816 and 1817.

Forecasts of short term volcanic activity are generated using an event tree process that is driven by a set of empirical statistical models derived through logistic regression. Each of the logistic models are constructed from a sparse and geographically diverse dataset that was assembled from a collection of historic volcanic unrest episodes. The dataset consists of monitoring measurements (e.g. seismic), source modeling results, and historic eruption information. Incorporating this data into a single set of models provides a simple mechanism for simultaneously accounting for the geophysical changes occurring within the volcano and the historic behavior of analog volcanoes. A bootstrapping analysis of the training dataset allowed for the estimation of robust logistic model coefficients. Probabilities generated from the logistic models increase with positive modeling results, escalating seismicity, and high eruption frequency. The cross validation process produced a series of receiver operating characteristic (ROC) curves with areas ranging between 0.78 - 0.81, which indicate the algorithm has good predictive capabilities. In addition, ROC curves also allowed for the determination of a false positive rate and optimum detection threshold for each stage of the algorithm. The results demonstrate the logistic models are highly transportable and can compete with, and in some cases outperform, non-transportable empirical models trained with site specific information. The incorporation of source modeling results into the event tree’s decision making process has begun the transition of volcano monitoring applications from simple mechanized pattern recognition algorithms to a physical model based forecasting system.

L'augmentation artificielle de la couche stratosphérique d'aérosol de sulfate a été proposée comme méthode pour réduire le réchauffement climatique causé par les émissions anthropiques de gaz à effet de serre. Dans cette thèse, nous présentons un modèle global atmosphère-aérosol nouvellement développé, évaluons sa performance par rapport aux observations et l'appliquons pour étudier l'efficacité et les impacts de cette forme possible d'ingénierie climatique. Nous trouvons que l'effet de refroidissement réalisable par unité de masse de soufre injectée peut diminuer de façon plus drastique qu'estimé précédemment pour des taux d'injection élevés et que des injections à plus haute altitude ou dans des régions plus grandes n'entraînent pas un refroidissement plus fort. L'efficacité de la méthode pourrait donc être plutôt limitée, tout au moins dans les cas d'injections tropicales de dioxyde de soufre que nous avons modélisées. Par ailleurs, il existe plusieurs effets secondaires potentiellement nocifs, tels que le chauffage stratosphérique dû à l'absorption de rayonnement par l'aérosol provoquant de fortes perturbations dans la dynamique atmosphérique, la composition chimique de la stratosphère et les nuages hauts. Enfin, nous trouvons que les effets radiatifs de l'injection d'aérosol stratosphérique et de l'éclaircissement des nuages marins, une autre technique de géo-ingénierie proposée, seraient largement additifs et complémentaires lors de leur application parallèle. Cela pourrait permettre de concevoir un port-folio d'approches pour atteindre des objectifs climatiques spécifiques et réduire les effets secondaires indésirables de l'ingénierie climatique. / The enhancement of the stratospheric sulphate aerosol layer has been proposed as a method to abate the global warming caused by anthropogenic greenhouse gas emissions. In this thesis we present a newly developed global atmosphere-aerosol model, evaluate its performance against observations, and apply it to study the effectiveness and impacts of this possible form of climate engineering. We find that the achievable cooling effect per injected sulphur mass unit may decrease more drastically for larger injections than previously estimated and that injections at higher altitude or over larger areas do not result in a stronger cooling. The effectiveness of the method may therefore be rather limited, at least when using tropical injections of sulphur dioxide as in our model experiments. In addition, there are several potentially harmful side effects, such as stratospheric heating due to absorption of radiation by the aerosol causing strong perturbations in atmospheric dynamics, composition, and high-level clouds. Furthermore, we find that the radiative effects of stratospheric aerosol injection and marine cloud brightening, another proposed geoengineering technique, would be largely additive and complementary when applying them together. This might allow the design of portfolio approaches to achieve specific climate goals and reduce unintended side effects of climate engineering.

The Arctic radiation climate is influenced substantially by anthropogenic and natural aerosols. There have been numerous studies devoted to understanding the radiative impacts of anthropogenic aerosols (e.g. those responsible for producing the Arctic haze phenomenon) and natural aerosols (e.g. dust and smoke) on the Arctic environment, but volcanic aerosols have received less attention. Volcanic eruptions occur frequently in the Arctic and have the capacity to be long duration, high intensity events, expelling large amounts of aerosol-sized ash and gases, which form aerosols once in the atmosphere. Additionally, volcanic eruptions deposit ash, which can alter the surface reflectivity, and remain to influence the radiation balance long after the eruptive plume has passed over and dissipated. The goal of this dissertation is to quantify the radiative effects of volcanic aerosols in the Arctic caused by volcanic plumes and deposits onto ice and snow covered surfaces. The shortwave, longwave, and net direct aerosol radiative forcing efficiencies and atmospheric heating/cooling rates caused by volcanic aerosol from the 2009 eruption of Mt. Redoubt were determined by performing radiative transfer modeling constrained by NASA A-Train satellite data. The optical properties of volcanic aerosol were calculated by introducing a compositionally resolved microphysical model developed for both ash and sulfates. Two compositions of volcanic aerosol were considered in order to examine a fresh, ash rich plume and an older, ash poor plume. The results indicate that environmental conditions, such as surface albedo and solar zenith angle, can influence the sign and the magnitude of the radiative forcing at the top of the atmosphere and at the surface. Environmental conditions can also influence the magnitude of the forcing in the aerosol layer. For instance, a fresh, thin plume with a high solar zenith angle over snow cools the surface and warms the top of the atmosphere, but the opposite effect is seen by the same layer over ocean. The layer over snow also warms more than the same plume over seawater. It was found that plume aging can alter the magnitude of the radiative forcing. For example, an aged plume over snow at a high solar zenith angle would warm the top of the atmosphere and layer by less than the fresh plume, while the aged plume cools the surface more. These results were compared with those reported for other aerosols typical to the Arctic environment (smoke from wildfires, Arctic haze, and dust) to demonstrate the importance of volcanic aerosols. It is found that the radiative impacts of volcanic aerosol plumes are comparable to those of other aerosol types, and those compositions rich in volcanic ash can have greater impacts than other aerosol types. Volcanic ash deposited onto ice and snow in the Arctic has the potential to perturb the regional radiation balance by altering the surface reflectivity. The areal extent and loading of ash deposits from the 2009 eruption of Mt. Redoubt were assessed using an Eulerian volcanic ash transport and dispersion model, Fall3D, combined with satellite and deposit observations. Because observations are often limited in remote Arctic regions, we devised a novel method for modeling ash deposit loading fields for the entire eruption based on best-fit parameters of a well-studied eruptive event. The model results were validated against NASA A-train satellite data and field measurements reported by the Alaska Volcano Observatory. Overall, good to moderate agreement was found. A total cumulative deposit area of 3.7 X 10^6 km2 was produced, and loadings ranged from ~7000 ± 3000 gm-2 near the vent to <0.1 ± 0.002 gm-2 on the outskirts of the deposits. Ash loading histories for total deposits showed that fallout ranged from ~5 – 17 hours. The deposit loading results suggest that ash from short duration events can produce regionally significant deposits hundreds of kilometers from the volcano, with the potential of significantly modifying albedo over wide regions of ice and snow covered terrain. The solar broadband albedo change, surface radiative forcing, and snowmelt rates associated with the ash deposited from the 2009 eruption of Mt. Redoubt were calculated using the loadings from Fall3D and the snow, ice, and aerosol radiative models. The optical properties of ash were calculated from Mie theory, based on size information recovered from the Fall3D model. Two sizes of snow were used in order to simulate a young and old snowpack. Deposited ash sizes agree well with field measurements. Only aerosol-sized ashes in deposits were considered for radiative modeling, because larger particles are minor in abundance and confined to areas very close to the vent. The results show concentrations of ash in snow range from ~ 6.9x10^4 – 1x10^8 ppb, with higher values closer to the vent and lowest at the edge of the deposits, and integrated solar albedo reductions of ~ 0 – 59% for new snow and ~ 0 – 85% for old snow. These albedo reductions are much larger than those typical for black carbon, but on the same order of magnitude as those reported for volcanic deposits in Antarctica. The daily mean surface shortwave forcings associated with ash deposits on snow ranged from 0 – 96 Wm-2 from the outmost deposits to the vent. There were no significantly accelerated snowmelts calculated for the outskirts of the deposits. However, for areas of higher ash loadings/concentrations, daily melt rates are significantly higher (~ 220 – 320%) because of volcanic ash deposits.

The chronology of the Late Bronze and Early Iron Age Near East is currently a topic of intense scholarly debate. The conventional/orthodox chronology for this period has been assembled over the past one-two centuries using information from King-lists, royal annals and administrative documents, primarily those from the Great Kingdoms of Egypt, Assyria and Babylonia. This major enterprise has resulted in what can best be described as an extremely complex but little understood jigsaw puzzle composed of a multiplicity of loosely connected data. I argue in my thesis that this conventional chronology is fundamentally wrong, and that Egyptian New Kingdom (Memphite) dates should be lowered by 200 years to match historical actuality. This chronological adjustment is achieved in two stages: first, the removal of precisely 85 years of absolute Assyrian chronology from between the reigns of Shalmaneser II and Ashur-dan II; and second, the downward displacement of Egyptian Memphite dates relative to LBA Assyrian chronology by a further 115 years. Moreover, I rely upon Kuhnian epistemology to structure this alternate chronology so as to make it methodologically superior to the conventional chronology in terms of historical accuracy, precision, consistency and testability.