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Poluianov, S. V. (Stepan V. ). "Proxies for long-term cosmic ray variability." Doctoral thesis, Oulun yliopisto, 2019. http://urn.fi/urn:isbn:9789526213743.
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Abstract The thesis is focused on the reconstruction of long-term cosmic ray variability using proxy data. The 11-year solar cycle in production/deposition rates of cosmogenic nuclides ¹⁰Be and ¹⁴C has been modelled for the conditions of grand minima and maxima of solar activity (namely, Maunder Minimum and Grand Modern Maximum). The result shows that contrary to the observed strongly suppressed amplitude of the solar cycle in sunspots during Maunder Minimum relatively to Grand Modern Maximum, the cosmic ray proxies have the comparable amplitudes during the two periods. This phenomenon is caused by the nonlinear relation between solar activity and production of cosmogenic nuclides. In addition to well-established proxies of cosmic rays, nitrate in polar ice has been recently proposed as a new proxy for the long-term variability of galactic cosmic rays. The thesis contains two tests of its applicability for this purpose with TALDICE and EPICA-Dome C ice core data from Central Antarctica. The results support the proposal for the multimillennial time scales. Lunar samples acquired during the Apollo missions are important data for estimating the averaged energy spectra of galactic cosmic rays and solar energetic particles at the Earth’s orbit. The development in modelling of the interaction between energetic particles and matter makes it necessary to revise the earlier results. Because of that, new production rates of ¹⁰Be and ¹⁴C in lunar samples by galactic cosmic rays and solar energetic particles have been computed. New accurate cosmic ray reconstructions from natural archives containing cosmogenic nuclides use sophisticated climatic models requiring yield functions of the nuclides with high altitude resolution. These functions have been computed for ⁷Be, ¹⁰Be, ¹⁴C, ²²Na, and ³⁶Cl in the Earth’s atmosphere. Overall, the major purpose of the studies presented in the thesis is to increase the quality of reconstructions of the long-term cosmic ray variability for better understanding of the solar and heliospheric physics<br>Original papers The original publications are not included in the electronic version of the dissertation. Poluianov, S. V., Usoskin, I. G., & Kovaltsov, G. A. (2014). Cosmogenic Isotope Variability During the Maunder Minimum: Normal 11-year Cycles Are Expected. Solar Physics, 289(12), 4701–4709. https://doi.org/10.1007/s11207-014-0587-6 Poluianov, S., Traversi, R., & Usoskin, I. (2014). Cosmogenic production and climate contributions to nitrate record in the TALDICE Antarctic ice core. Journal of Atmospheric and Solar-Terrestrial Physics, 121, 50–58. https://doi.org/10.1016/j.jastp.2014.09.011 Poluianov, S., Artamonov, A., Kovaltsov, G., & Usoskin, I. (2015). Energetic particles in lunar rocks: Production of cosmogenic isotopes. Proceedings of Science, 30-July-2015, art. no. 051 . Traversi, R., Becagli, S., Poluianov, S., Severi, M., Solanki, S. K., Usoskin, I. G., & Udisti, R. (2016). The Laschamp geomagnetic excursion featured in nitrate record from EPICA-Dome C ice core. Scientific Reports, 6(1). https://doi.org/10.1038/srep20235 Poluianov, S. V., Kovaltsov, G. A., Mishev, A. L., & Usoskin, I. G. (2016). Production of cosmogenic isotopes 7Be, 10Be, 14C, 22Na, and 36Cl in the atmosphere: Altitudinal profiles of yield functions. Journal of Geophysical Research: Atmospheres, 121(13), 8125–8136. https://doi.org/10.1002/2016jd025034
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Tang, Sumin. "Exploring the Long-Term and Extreme Variability of Stars." Thesis, Harvard University, 2012. http://dissertations.umi.com/gsas.harvard:10369.
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This thesis presents observational studies of long-term and extreme variability of stars with the Digital Access to a Sky Century@Harvard (DASCH) project. Stellar variations over decades are poorly explored. With the unique 100 years coverage of DASCH, for the first time, we are able to study the variable sky over long timescales in a systematic way. I have developed photometric calibration and variable search algorithms for DASCH. I have discovered exciting new types of long-term variables, which do not match any of the common classes, and studied the physical processes involved. Following a brief introduction on variable stars and DASCH in the first chapter, I describe my work on DASCH pipeline, including photometric development and defect filtering in chapter 2. I present our discovery of a group of peculiar long-term K giant variables with \(\sim1\) mag variations over decades in chapter 3. Follow-up observations show that they consist of two subgroups, including a subgroup of RS CVn binaries with strong magnetic activity, and another subgroup of single stars. In both cases, the variation amplitudes and timescales are abnormal, and may be related to either ultra strong star spots, or novel dust formation processes. In chapter 4, I present the discovery of a 5 yr dip around 1900 in the eclipsing binary KU Cyg consisting of a F star and a K giant, which is related to the accretion disk surrounding the F star. It showed a slow fading \((\sim 4 yr)\), which is probably caused by increases in dust extinction in the disk, and a relatively fast brightening \((\sim 1 yr)\), which may be due to the evaporation of dust transported inward through the disk. The extinction excess which caused the fading may arise from an increased mass transfer rate in the system or from dust clump ejections from the K giant, in accordance with K giant “dimming” as discussed above. In chapter 5, I present a 10 yr nova-like outburst in a peculiar symbiotic system. With P = 119 days, it is interestingly located in the period gap region between classical novae and symbiotic novae. The most probable explanation of the outburst is hydrogen shell-burning on the white dwarf (WD) without significant mass loss, which suggests a promising new channel for Type Ia Supernovae (SNe). In chapter 6, I present the DASCH light curves of Kepler planet-candidate host stars. We found no variation for these host stars. In chapter 7, I present my variable search algorithms and the resulting DASCH variable catalog for the Kepler field. The conclusion is presented in chapter 8.<br>Astronomy
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Mullen, Thomas James. "A system identification approach to characterizing intermediate term hemodynamic variability." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/10011.
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Thesis (Ph. D.)--Harvard--Massachusetts Institute of Technology Division of Health Sciences and Technology, 1998.<br>Includes bibliographical references (p. 157-170).<br>by Thomas James Mullen.<br>Ph.D.
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Susilo, Yusak Octavius. "The Short-term Variability and the Long-term Changes of Individual Spatial Behavior in Urban Areas." 京都大学 (Kyoto University), 2005. http://hdl.handle.net/2433/123476.
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Kornisch, Myriam. "Visual and Verbal Short-Term Memory Correlates of Variability in Vocabulary Size." Thesis, University of Canterbury. Communication Disorders, 2012. http://hdl.handle.net/10092/6737.
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This study investigated the relationship between working memory and language in typically developing young children. The aim was to gain a better understanding of language development, in particular, the involvement of visual and verbal short-term memory in language acquisition and its influence on vocabulary size. It explored possible underlying causes of why some children have problems in the process of learning to talk, whereas other children acquire language easily. A total of 51 New Zealand English speaking children aged two to five completed a battery of assessments measuring receptive and expressive vocabulary and visual and verbal short-term memory. The standardized tests administered included the Receptive One Word Picture Vocabulary Test (Brownell, 2000b), the Expressive One Word Picture Vocabulary Test (Brownell, 2000a), the Visual Patterns Test (Stokes, Klee, Cruickshank, & Pleass, 2009), and the Test of Early Nonword Repetition (Stokes & Klee, 2009a). Receptive vocabulary knowledge was strongly associated with visual (r = .75) and verbal (r = .60) short-term memory performance and age (r = .72). The relationship of expressive vocabulary to visual short-term memory (r = .80) was stronger than to verbal short-term memory (r = .62) but significant for both and also for age (r= .83). Significant unique predictors for expressive vocabulary were age (R2 change = .60) as well as visual (R2 change = .04) and verbal (R2 change = .04) short-term memory. However, age appeared to be the only unique predictor for receptive vocabulary (R2 change = .54). In addition, the findings suggested that visual and verbal short-term memory increases as children get older. Hence, the Visual Patterns Test and Test of Early Nonword Repetition seem to be good predictors, over and above age, of expressive vocabulary knowledge.
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Muncaster, Ryan. "Modelling the effects of short-term solar variability on stratospheric chemistry." Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=67042.
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A new stratospheric chemistry box model with a more accurate on-line photolysis calculation is used to study the effects of daily solar variability on stratospheric chemistry, both with and without dynamics. The chemical response on this time-scale has not been looked at before. The underlying mechanisms behind the chemical response are thoroughly analyzed using a step-by-step approach. The daily response is found to have the ability to be extrapolated to longer time-scales, specifically the 27-day cycle, and the inclusion of dynamics is found to reduce the response of ozone to solar variability. Also, the detailed analysis of chemical species other than ozone fills a gap in current research.<br>Un nouveau modèle de boîte pour la chimie stratosphérique a été développé et est utilisé pour étudier les effets journaliers de la variabilité solaire sur la chimie stratosphérique, avec ou sans dynamique atmosphérique. La réponse chimique sur cette échelle de temps n'avait pas été étudiée. Les mécanismes sous-jacents à la réponse chimique sont analysés dans les détails en incluant progressivement les différents couplages. En outre, il est montré que la réponse journalière peut êtreextrapolée sur de plus longues échelles de temps, en particuliers pour le cycle de 27 jours. Lorsque la dynamique est introduite, il est montré que le signal en est diminué. L'analyse détaillée des espèces chimiques autres que l'ozone comble un manque dans l'éetat de la recherche actuelle.
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Sanchez, Margaux. "Évolution de l’asthme au long cours : aspects méthodologiques et lien avec la pollution atmosphérique." Thesis, Paris 11, 2015. http://www.theses.fr/2015PA11T030/document.
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Contrairement à la majorité des maladies chroniques qui s’aggravent progressivement, l’expression de l’asthme est variable au cours du temps. L’asthme peut apparaître, disparaître, s’aggraver ou s’améliorer au cours de plusieurs années, voire une décennie, à tout âge de la vie. Cette variabilité à long terme est particulièrement mal décrite chez l’adulte car les données sont rares. Par une approche épidémiologique, la thèse a pour objectif de mieux comprendre la variabilité de l’expression de l’asthme au long cours chez l’adulte dans deux cohortes françaises : E3N, l’Étude Épidémiologique auprès des femmes de la Mutuelle Générale de l’Éducation Nationale et EGEA, l’étude Épidémiologique des facteurs Génétiques et Environnementaux de l’Asthme. Le premier axe, méthodologique, porte sur la mesure de la variabilité de l’expression de l’asthme au long cours. Le second axe, environnemental, porte sur le rôle de la pollution atmosphérique sur cette variabilité. Concernant l’axe méthodologique, l’étude des réponses à une unique question sur l’asthme répétée 7 fois sur 13 ans dans le cadre de la cohorte E3N a montré qu’une succession incohérente de réponses (positives et négatives) reflétait une partie de la variabilité de l’activité de l’asthme à moyen terme, suggérant l’intérêt de cette approche pour affiner la caractérisation de l’expression de la maladie au cours du temps. Dans le contexte d’un intérêt croissant pour la santé perçue, l’étude d’une question portant sur l’auto-évaluation rétrospective du changement dans la santé respiratoire au cours des 10 dernières années a montré que l’information ainsi obtenue était complémentaire de celle d’outils épidémiologiques et cliniques existants pour décrire la trajectoire à long terme de l’asthme, et permettait de prédire en partie l’évolution de l’asthme.À la suite d’une récente méta-analyse regroupant 6 cohortes européennes (avec 23 000 participants) dont les résultats suggèrent le rôle d’une exposition chronique à la pollution atmosphérique dans l’incidence de l’asthme chez l’adulte, une analyse a porté sur l’évolution des traitements de fond et de secours de l’asthme sur une période de 4 ans en lien avec la pollution atmosphérique. Chez les femmes asthmatiques de la cohorte E3N, plus l’exposition chronique au dioxyde d’azote et aux particules était élevée, plus la consommation de corticoïdes inhalés augmentait au cours du temps, suggérant le rôle à long terme du dioxyde d’azote dans la progression de l’asthme. En conclusion, les résultats de la thèse montrent que des outils simples, tels que l’utilisation de réponses successives à une unique question sur l’asthme et l’auto-évaluation du changement dans la santé respiratoire sur 10 ans, peuvent être utilisés pour mieux caractériser la variabilité de l’expression de l’asthme au long cours, de façon complémentaire aux outils déjà existants. Associés à ceux de la littérature, les résultats de la thèse soutiennent le rôle délétère d’une exposition chronique à la pollution de l’air extérieur sur l’évolution de l’asthme au long cours et renforcent l’intérêt d’interventions de santé publique visant à diminuer la concentration des polluants atmosphériques<br>Unlike most chronic diseases, which tend to get progressively worse over time, the expression of asthma is variable over time. Asthma may onset at any age and is known to clinically persist, possibly resolve, or present any combination of remissions and relapses over several years, even decades. Such long-term variability has been difficult to describe in adults as data are scarce. Through an epidemiological approach, the aim of the thesis is to gain a better understanding of the variability of asthma expression over the long term in adults, in two French cohorts: the E3N study (l’Étude Épidémiologique auprès des femmes de la Mutuelle Générale de l’Éducation Nationale) and the EGEA study (the Epidemiological study on the Genetics and Environment of Asthma). The first axis is methodological and relates to the characterization of asthma expression variability over the long term. The second axis is environmental and related to the effect of air pollution on such long-term variability. Regarding the methodological axis, the in-depth analysis of answers to a single question on ever asthma repeated 7 times over 13 years in the E3N study has shown that apparently inconsistent succession of answers (positive and negative) could capture part of the medium-term variability of asthma activity, suggesting the usefulness of such approach to improve the characterization of asthma expression over time. In a context of growing interest for perceived health, a simple retrospective self-assessment of 10-year change in respiratory health has been shown to provide complementary insights to classical epidemiological and clinical tools to describe the long-term trajectory of asthma, and could predict part of the asthma evolution. Following a recent meta-analysis including 6 European cohorts (23000 participants), in which results suggest a deleterious effect of chronic ambient air pollution on asthma incidence in adults, an analysis investigated the evolution of asthma medication dispensations over 4 consecutive years, in relation with air pollution. Among the women with asthma in the E3N study, an increased estimated exposure to outdoor nitrogen dioxide and particles was associated with increased rate of controller dispensations over time, suggesting the long-term effect of air pollution on asthma progression. In conclusion, results of the thesis showed that simple tools such as several repeated answers to a single question on asthma and the self-assessment of long-term change in respiratory health may be useful in order to better characterize the variability of asthma expression over the long term, as a complementary approach alongside with classical tools. Combined with the literature, results of the thesis support the deleterious impact of chronic air pollution on progression of asthma and strengthen the need of public health interventions to reduce air pollutants concentration
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Kim, Taehyung. "Analysis of variability in car-following behavior over long-term driving maneuvers." College Park, Md. : University of Maryland, 2005. http://hdl.handle.net/1903/3048.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2005.<br>Thesis research directed by: Civil Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Navarro-Perez, Eleuteria. "Physical oceanography of the Canary current : short term, seasonal and interannual variability." Thesis, Bangor University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318561.
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Persson, Söderman Jennie. "A Study of the Short-term Variability of Seawater pCO2 near Östergarnsholm." Thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-222286.
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In this study, an analysis of upwelling and biological activities impact on the seawater pCO2 variability was done to improve the knowledge about the pCO2 variability in seawater in the Baltic Sea. During upwelling activity, CO2 rich waters are upwelled to the surface. This influences air-sea CO2 flux and thus the net uptake/emission of CO2 by the sea. pCO2 and SST measurements from a SAMI sensor, located at the Östergarnsholm site in the Baltic Sea, and SST satellite data, was used to identify periods affected by upwelling activity. A strong variability due to upwelling activity was observed on the pCO2 concentration. The frequency of upwelling activity at the Östergarnsholm site was estimated to be around 20 % of the time from May-November. The relationship between pCO2 and SST during upwelling activity was found to depend of the month. In November, this relationship can be used to characterise the effect of upwelling, but for the other months there are no differences between the none- upwelling periods and the upwelling periods. Another type of period, characterized by a diurnal variability of pCO2 mainly driven by the biological effect, was also observed.<br>I denna studie undersöktes hur uppvällning och biologisk aktivitet påverkar koncentrationen av pCO2 i havet. Detta gjordes för att få ökad förståelse för korttidsvariationen av pCO2 i Östersjön. Under uppvällning pressas CO2-rikt vatten upp till ytan. Detta påverkar flödet av CO2 mellan hav och atmosfär och då även det totala upptaget/utsläppet av CO2 från havet. I studien användes pCO2 och SST mätningar från en SAMI-sensor, placerad vid Östergarnsholm i Östersjön, och en del satellitdata för att identifiera perioder påverkade av uppvällning. Det observerades att uppvällnings inverkan på koncentrationen av pCO2 varierar kraftigt. Frekvensen av uppvällning vid Östergarnsholm uppskattades vara ungefär 20 % av tiden under maj-november. Relationen mellan SST och pCO2 under perioder med uppvällning observerades variera från maj-november. I november kan denna relation användas till att uppskatta effekten av uppvällning men under de andra månaderna är relationen under uppvällning för lika relationen under icke- uppvällning. Även en annan slags perioder observerades; under dessa perioder observerades en dygnscykel av pCO2, driven av biologisk aktivitet.
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Hittinger, Eric Stephen. "Energy Storage on the Grid and the Short-term Variability of Wind." Research Showcase @ CMU, 2012. http://repository.cmu.edu/dissertations/127.
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Wind generation presents variability on every time scale, which must be accommodated by the electric grid. Limited quantities of wind power can be successfully integrated by the current generation and demand-side response mix but, as deployment of variable resources increases, the resulting variability becomes increasingly difficult and costly to mitigate. In Chapter 2, we model a co-located power generation/energy storage block composed of wind generation, a gas turbine, and fast-ramping energy storage. A scenario analysis identifies system configurations that can generate power with 30% of energy from wind, a variability of less than 0.5% of the desired power level, and an average cost around $70/MWh.
While energy storage technologies have existed for decades, fast-ramping grid-level storage is still an immature industry and is experiencing relatively rapid improvements in performance and cost across a variety of technologies. Decreased capital cost, increased power capability, and increased efficiency all would improve the value of an energy storage technology and each has cost implications that vary by application, but there has not yet been an investigation of the marginal rate of technical substitution between storage properties. The analysis in chapter 3 uses engineering-economic models of four emerging fast-ramping energy storage technologies to determine which storage properties have the greatest effect on cost-of-service. We find that capital cost of storage is consistently important, and identify applications for which power/energy limitations are important.
In some systems with a large amount of wind power, the costs of wind integration have become significant and market rules have been slowly changing in order to internalize or control the variability of wind generation. Chapter 4 examines several potential market strategies for mitigating the effects of wind variability and estimate the effect that each strategy would have on the operation and profitability of wind farms. We find that market scenarios using existing price signals to motivate wind to reduce variability allow wind generators to participate in variability reduction when the market conditions are favorable, and can reduce short-term (30-minute) fluctuations while having little effect on wind farm revenue.
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Yaczola, Stephen A. "MEASURING THE LONG-TERM IMPACT OF LABOR CAPACITY MANAGEMENT ON PERFORMANCE VARIABILITY." Cleveland State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=csu1556616391821583.
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Ulrich, Heather Marie. "Examining the variability in the long term adjustment of child sexual abuse victims." The University of Montana, 2008. http://etd.lib.umt.edu/theses/available/etd-09202007-123302/.
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Two meta-analyses (Rind, Tromovitch & Bauserman, 1998; Ulrich, Randolph, & Acheson, 2006) have suggested that the long held belief about the inevitable pervasive negative effects of child sexual abuse does not hold for college populations. The meta-analyses suggest that there is other factors in sexual abuse victims' lives that interact with their abuse experience to produce the sometimes-observed minimal long-term effects on psychological adjustment. This research attempted to examine a potential model for explaining the variability in the long-term effects of child sexual abuse by examining both moderator variables and abuse characteristics within the same population. The study examined three potential moderators, attributional style (including abuse specific attributions), family environment, and social support. Abuse characteristics were also entered in the moderator regression analyses, in order to examine the variance accounted for by each variable on long-term outcome beyond any shared variance between variables. It was hypothesized that there would be a significant difference between subjects reporting a history of sexual abuse and those without a history of sexual abuse on their long term psychological adjustment. This difference would be minimal, but would indicate that those without a history of child sexual abuse score better on a measure of trauma psychopathology. The second hypothesis was that attributional style, family environment, and social support would moderate the long-term outcome of child sexual abuse victims, beyond the variance accounted for by the abuse characteristics. The final hypothesis was that the accumulation of the aforementioned risk factors would result in a worse long-term outcome in college populations. This model attempted to provide an understanding of the relationship between each variable with long term outcome of child sexual abuse, as well as the cumulative effect of all these variables on the relationship of child sexual abuse outcomes. Results suggested that social support satisfaction and the victim's attributions about the cause of the child sexual abuse experience were related to trauma outcomes. In addition, the results provided potential indications for what to target in treatment based upon symptom presentation in child sexual abuse victims.
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Xia, Lan [Verfasser], and Hans Von [Akademischer Betreuer] Storch. "Long-term variability of storm tracks characteristics / Lan Xia. Betreuer: Hans von Storch." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2013. http://d-nb.info/1031756795/34.
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Connelly, Samuel. "The long-term X-ray, UV and optical variability of active galactic nuclei." Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/400647/.
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The variability of emission from active galactic nuclei (AGN), both intrinsic, due to changes in the emitting regions, and extrinsic, due to absorption and scattering from material near to the black hole, can reveal a wealth of information about their geometry and accretion behaviour. In this thesis, I use analysis of the spectral variability of the Xray, UV/optical emission from AGN to probe the properties of the material surrounding supermassive black holes at their centres. Firstly, I present constraints on the variability of the photon index of the X-ray spectrum of 24 Swift AGN from the Palomar sample of galaxies. The change in the behaviour of AGN from ‘softer-brighter’ to ‘harder-when-brighter’ at a critical accretion rate, seen previously in other samples of AGN, is found. ‘Harder-when-brighter’ behaviour is measured in several sources individually, achieved previously in only one AGN. I present a study of the long-term (months-years) X-ray spectral variability of three Seyfert AGN known to exhibit strong absorption variations. Trends in the long-term behaviour of the absorbers, in particular a strong anti-correlation between the observed absorbing column and the intrinsic luminosity of NGC 1365, are explained using a variable wind model. In this model, the radius at which the wind arises is dependent on the luminosity of the central engine, leading to correlated long-time-scale changes in the observed absorption properties. Finally, time lags between the X-ray and UV/optical variability of the Seyfert AGN NGC 4395 are measured, using cross-correlation techniques. The lags fit the ?4/3 dependence expected from reprocessing of X-rays in the accretion disc. Modelling of the expected lags from a standard Shakura-Sunyaev thin disc with the previously-measured physical parameters of the system is then carried out. The results are consistent with the data, further supporting reprocessing as the principle source of UV/optical variability in NGC 4395.
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Todd, Beverley. "Reconstructing long-term records of UK drought and analysis of variability, 1697-2013." Thesis, University of Liverpool, 2014. http://livrepository.liverpool.ac.uk/2011366/.
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Droughts are one of the most widespread and complex natural hazards, and remain poorly understood in the context of the United Kingdom. Although the UK is perceived as a relatively water rich country, droughts are a recurrent feature of its climate, causing widespread and serious environmental and economic impacts. Current understanding of drought risk is often based on relatively short records, and/or a small number of specific contemporary case study events from the last couple of decades (e.g. 1976). This study addresses this problem through the development of long (>150 year) meteorological drought records reconstructed using the self-calibrating Palmer Drought Severity Index (scPDSI). The index was calculated using long duration temperature and rainfall records. New rainfall series were generated for Carlisle and Chatsworth, existent rainfall series were extended for Kew, Spalding, Manchester, Edinburgh and Oxford. Additional rainfall series were kindly provided for Appleby and Durham. Temperature series for the Lancashire Plain, Oxford, Edinburgh and Durham were also extended. Where appropriate the newly developed and existing series were evaluated and tested to ensure homogeneity. The drought reconstructions identify multiple drought-rich periods, particularly in the eighteenth and twentieth centuries, with an increasing tendency towards more severe droughts during the latter period. Prolonged rainfall deficiencies are found to be the primary cause of severe droughts, with rising temperatures exacerbating the rainfall conditioned drought pattern. Cycles at the 6-10 year period identify a sub-decadal to decadal signal during the more drought-rich periods, which can be interpreted as reflecting large scale modes of climate variability. Analysis of the spatial variability of droughts finds that whilst severe events predominantly display spatial coherence, there are notable variations in drought characteristics (severity and duration) that reflect intra- and interregional variability in drought behaviour. In part this can be attributed to localised variations in rainfall and distance between sites. This study extends the temporal range of previous drought studies and places recent drought events in a longer context, improving upon existing ‘benchmark’ drought analyses; with far-reaching implications for local, national and continental scale reduction of drought vulnerability and risk.
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Egeland, Ricky Alan. "Long-Term Variability of the Sun in the Context of Solar-Analog Stars." Thesis, Montana State University, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10267829.
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<p> The Sun is the best observed object in astrophysics, but despite this distinction the nature of its well-ordered generation of magnetic field in 11-year activity cycles remains a mystery. In this work, we place the solar cycle in a broader context by examining the long-term variability of solar analog stars within 5% of the solar effective temperature, but varied in rotation rate and metallicity. Emission in the Fraunhofer H & K line cores from singly-ionized calcium in the lower chromosphere is due to magnetic heating, and is a proven proxy for magnetic flux on the Sun. We use Ca H & K observations from the Mount Wilson Observatory HK project, the Lowell Observatory Solar Stellar Spectrograph, and other sources to construct composite activity time series of over 100 years in length for the Sun and up to 50 years for 26 nearby solar analogs. Archival Ca H & K observations of reflected sunlight from the Moon using the Mount Wilson instrument allow us to properly calibrate the solar time series to the S-index scale used in stellar studies. We find the mean solar <i>S</i>-index to be 5–9% lower than previously estimated, and the amplitude of activity to be small compared to active stars in our sample. A detailed look at the young solar analog HD 30495, which rotates 2.3 times faster than the Sun, reveals a large amplitude ~12-year activity cycle and an intermittent short-period variation of 1.7 years, comparable to the solar variability time scales despite its faster rotation. Finally, time series analyses of the solar analog ensemble and a quantitative analysis of results from the literature indicate that truly Sun-like cyclic variability is rare, and that the amplitude of activity over both long and short timescales is linearly proportional to the mean activity. We conclude that the physical conditions conducive to a quasi-periodic magnetic activity cycle like the Sun’s are rare in stars of approximately the solar mass, and that the proper conditions may be restricted to a relatively narrow range of rotation rates.</p>
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Benlloch, García Sara. "Long-term x-ray variability of active galactic nuclei and x-ray binaries." [S.l. : s.n.], 2004. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB11051893.
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Lockard, Brendan Corbett. "Long Term Hydrologic Effects on Stream Health from Residential Development Patterns." Thesis, Virginia Tech, 2002. http://hdl.handle.net/10919/34013.
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In this study eight residential development scenarios are created for the mostly undeveloped Back Creek Watershed outside Roanoke, Virginia. The development scenarios include low, medium (cluster), medium (conventional), and high density development with and without development restrictions. These scenarios represent a large range of development as the land use imperviousness varies from 1% for the baseline condition to 34% for the most developed scenario. The hydrologic model HSPF is used to generate overland and channel flows from 43 years of rainfall. <p>
Hydrologic output from HSPF of the various landuse patterns from the eight scenarios are evaluated using Post Processor, a Visual Basic program. The results show that increased development causes a reduction in Back Creek's baseflow and an increase in the occurrence of both high and low flow extreme events. Overall, these results indicate that increased development will increase the variability of flowrate in Back Creek.</p><p>
Stream health impacts from flow variability were also analyzed with the Post Processor. First, hydrologic statistical variables with ecological relationships were used to gage the level of stream health impacts from flow variability. The averaged stream health index for the development scenarios was found to closely follow the amount of development, represented by the percent of impervious landuse. Second, the amount of velocity, depth, and both depth and velocity habitat available for three habitat guild representative species was evaluated for each scenario. The results indicated that increased development would lead to a substantial reduction in available riffle species habitat (represented by the fantail darter) and a moderate reduction in run and pool species habitat (represented by the central stoneroller and smallmouth bass, respectively). </p><p>
Overall, increased development has been found to have a negative impact on stream health. This impact should be considered in any future expansion of the Roanoke suburbs into this watershed.</p><br>Master of Science
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Kritharas, Petros. "Developing a SARIMAX model for monthly wind speed forecasting in the UK." Thesis, Loughborough University, 2014. https://dspace.lboro.ac.uk/2134/16350.
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Wind is a fluctuating source of energy and, therefore, it can cause several technical impacts. These can be tackled by forecasting wind speed and thus wind power. The introduction of several statistical models in this field of research has brought to light promising results for improving wind speed predictions. However, there is not converging evidence on which is the optimal method. Over the last three decades, significant research has been carried out in the field of short-term forecasting using statistical models though less work focuses on longer timescales. The first part of this work concentrated on long-term wind speed variability over the UK. Two subsets have been used for assessing the variability of wind speed in the UK on both temporal and spatial coverage over a period representative of the expected lifespan of a wind farm. Two wind indices are presented with a calculated standard deviation of 4% . This value reveals that such changes in the average UK wind power capacity factor is equal to 7%. A parallel line of the research reported herein aimed to develop a novel statistical forecasting model for generating monthly mean wind speed predictions. It utilised long-term historic wind speed records from surface stations as well as reanalysis data. The methodology employed a SARIMAX model that incorporated monthly autocorrelation of wind speed and seasonality, and also included exogenous inputs. Four different cases were examined, each of which incorporated different independent variables. The results disclosed a strong association between the independent variables and wind speed showing correlations up to 0.72. Depending on each case, this relationship occurred from 4- up to 12-month lags. The inter comparison revealed an improvement in the forecasting accuracy of the proposed model compared to a similar model that did not take into account exogenous variables. This finding demonstrates the indisputable potential of using a SARIMAX for long-term wind speed forecasting.
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Soukharev, B. E., and L. L. Hood. "Solar cycle variation of stratospheric ozone: Multiple regression analysis of long-term satellite data sets and comparisons with models." AMER GEOPHYSICAL UNION, 2006. http://hdl.handle.net/10150/623340.
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Previous multiple regression analyses of the solar cycle variation of stratospheric ozone are improved by (1) analyzing three independent satellite ozone data sets with lengths extending up to 25 years and (2) comparing column ozone measurements with ozone profile data during the 1992–2003 period when no major volcanic eruptions occurred. Results show that the vertical structure of the tropical ozone solar cycle response has been consistently characterized by statistically significant positive responses in the upper and lower stratosphere and by statistically insignificant responses in the middle stratosphere (∼28–38 km altitude). This vertical structure differs from that predicted by most models. The similar vertical structure in the tropics obtained for separate time intervals (with minimum response invariably near 10 hPa) is difficult to explain by random interference from the QBO and volcanic eruptions in the statistical analysis. The observed increase in tropical total column ozone approaching the cycle 23 maximum during the late 1990s occurred primarily in the lower stratosphere below the 30 hPa level. A mainly dynamical origin for the solar cycle total ozone variation at low latitudes is therefore likely. The amplitude of the solar cycle ozone variation in the tropical upper stratosphere derived here is somewhat reduced in comparison to earlier results. Additional data are needed to determine whether this upper stratospheric response is or is not larger than model estimates.
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Penzlin, Ana Isabel, Kristian Barlinn, Ben Min-Woo Illigens, Kerstin Weidner, Martin Siepmann, and Timo Siepmann. "Effect of short-term heart rate variability biofeedback on long-term abstinence in alcohol dependent patients – a one-year follow-up." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-230932.
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Background:
A randomized controlled study (RCT) recently showed that short-term heart rate variability (HRV) biofeedback in addition to standard rehabilitation care for alcohol dependence can reduce craving, anxiety and improve cardiovascular autonomic function. In this one-year follow-up study we aimed to explore whether completion of 2-week HRV-Biofeedback training is associated with long-term abstinence. Furthermore, we sought to identify potential predictors of post-treatment abstinence.
Methods:
We conducted a survey on abstinence in patients with alcohol dependence 1 year after completion of an RCT comparing HRV-biofeedback in addition to inpatient rehabilitation treatment alone (controls). Abstinence rates were compared and analysed for association with demographic data as well as psychometric and autonomic cardiac assessment before and after completion of the biofeedback training using bivariate and multivariate regression analyses.
Results:
Out of 48 patients who participated in the RCT, 27 patients (9 females, ages 42.9 ± 8.6, mean ± SD) completed our one-year follow-up. When including in the analysis only patients who completed follow-up, the rate of abstinence tended to be higher in patients who underwent HRV-biofeedback 1 year earlier compared to those who received rehabilitative treatment alone (66.7% vs 50%, p = ns). This non-significant trend was also observed in the intention-to-treat analysis where patients who did not participate in the follow-up were assumed to have relapsed (46,7% biofeedback vs. 33.3% controls, p = ns). Neither cardiac autonomic function nor psychometric variables were associated with abstinence 1 year after HRV-biofeedback.
Conclusion:
Our follow-up study provide a first indication of possible increase in long-term abstinence after HRVbiofeedback for alcohol dependence in addition to rehabilitation.
Trial registration: The original randomized controlled trial was registered in the German Clinical Trials Register (DRKS00004618). This one-year follow-up survey has not been registered.
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De, Jesus Alma Lorelei. "Urban ambient particles: Long-term spatio-temporal trends and impacts of different control measures." Thesis, Queensland University of Technology, 2021. https://eprints.qut.edu.au/207786/1/Alma%20Lorelei_De%20Jesus_Thesis.pdf.
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This thesis is a quantitative analysis of the spatial and temporal variability as well as trends of the particulate matter concentrations in the ambient urban air. The outcome provided a clear understanding on how the different metrics (particle number, particle mass and oxidative potential) were affected by mitigation measures and other important drivers such as emission sources and meteorological factors.
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Flores, Marco Antonio Salas. "Assessing the variability of long-term Mexican instrumental records and the ENSO modulating force." Thesis, University of East Anglia, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.504850.
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Undisputable evidence of global warming is accumulating from direct observations. Unfortunately, for some unanalysed regions of the world, the data coverage is still sparse (IPCC, 2007). This study aims to assess the changing patterns of precipitation and temperature across Mexico and the direct influence of EI Nino-Southern Oscillation. A network of 175 stations with precipitation and 52 with temperature of monthly data were built for the Principal Component Analysis (PCA) and the ENSO modulation assessments. A set of 35 stations with daily data for weather extremes analyses was also developed. Oblique-rotated (promax, k=2) solutions have been applied to the monthly datasets to regionalise groups of stations that are varying coherently. Extreme indices are calculated using the RClimDex in the daily time-series of rainfall and temperature. Finally, linear (Kendall's tau-b) and lag correlations have been applied to establish relationships between three different ENSO indices, the precipitation regional averages (resulting from PCA) and also with the weather extreme indices. A clear latitudinal transition is observed when the annual and wet (May-Oct) seasons of regional precipitation averages and extreme rainfall indices are correlated with the ENSO indices: wetter c.onditions are observed north of the tropic of cancer and below normal precipitation is dominant in the southern part of the country. Meanwhile, a national climatic picture of wetter conditions is observed when the standardised versions of the dry (Nov-Apr) season of the regional precipitation averages and the extreme precipitation indices are correlated with the ENSO indices; precipitation responds mainly close to the peak of EI Nino-like conditions. Warmer temperatures are observed when the extreme temperature indices are correlated with the ENSO indices. Nevertheless, the most significant results are seen in the minimum temperature related indices, although timing of response to the ENSO modulation is not as clear as in the case of precipitation.
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Wendt, Robert D. T. "Variability in hurricane boundary layer characteristics observed in a long-term NOAA dropsonde archive." Thesis, Monterey, California: Naval Postgraduate School, 2014. http://hdl.handle.net/10945/42751.
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Approved for public release; distribution is unlimited<br>The statistical properties of five boundary layer height definitions were examined in 6,593 NCAR GPS dropsonde observations of the hurricane environment. Based on similar composite analysis studies, these boundary layer height estimates were divided into two categories based on their analytical characteristics. Three dynamical methods of estimating the boundary layer height were combined with two thermodynamical methods of estimating the mixed layer depth to numerically interrogate the physical properties of hurricanes within two primary modes of variability: azimuthal and geographic region. The results confirmed the vertical bifurcation of dynamical and thermodynamical height estimates and indicated a consistent distinction in the radial variability of each class. Moreover, the tangential wind field was well-described by the modified Rankine vortex. A characteristic decrease in boundary layer height with decreasing radius to the storm center was expressed in four of the five definitions. The non-uniform azimuthal distribution of relative radial winds and ill-behaved inflow layer depths precluded meaningful comparisons of boundary layer height in the rear storm-relative semicircle. While boundary layer height estimates failed to exhibit any significant regional variability, the right-front storm-relative quadrant appeared to exhibit non-trivial increases in mean boundary layer height.
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Withrow, Scott. "Do People Recognize and Use Within-Person Variability When Making Performance Ratings." Bowling Green State University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1320692559.
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Webb, Alastair John Stewart. "Determinants of medium-term blood pressure variability and the related risks of stroke and dementia." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:cd97daf5-c6d7-4386-94d7-a710d8ea5292.
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Visit-to-visit variability in blood pressure (BP) increases stroke risk, independent of mean BP. However, its physiological validity, the ideal method of measurement and the mechanisms increasing cardiovascular risk are unclear. In meta-analyses of individual patient data, I pooled associations between BP variability and risk of stroke, all cardiovascular events and death. I then determined antihypertensive drug-class differences in cardiovascular risk, intra-individual (I-VR) and inter-individual BP variability (M-VR). In 500 Oxford Vascular Study (OXVASC) patients undergoing thrice-daily home (HBPM) and awake ambulatory monitoring (ABPM), associations between mean, maximum or variability in BP (CV-BP) were determined with premorbid BP, hypertensive arteriopathy (creatinine, aortic stiffness, cognitive impairment, stroke versus TIA and leukoaraiosis) and cardiovascular events. In 200 patients, I determined associations with pulsatility or stiffness (pulse wave velocity) in cerebral and aortic vessels. There was a 21% and 27% increased risk of stroke and myocardial infarction per standard deviation of CV-SBP in 318700 patients, independent of mean SBP. In 244,479 patients, SBP variability was reduced by CCBs and diuretics within (I-VR=0.89, 95% CI=0.82-0.96, p=0.0001) and between individuals (M-VR 0.83, 0.77-0.89, p<0.0001), especially in the first year of treatment, explaining drug class differences in stroke risk (OR=0.76, 0.68-0.87, p<0.0001). In OXVASC, drug class differences on day-to-day SBP variability were greatest immediately after waking. Residual hypertension after treatment on HBPM but not ABPM (BP>135/85) predicted recurrent cardiovascular events (HR 2.82, 1.44-5.51, p=0.002 vs. 1.48, 0.68-3.23, p=0.33), reflecting stronger associations with premorbid BP and hypertensive arteriopathy, due largely to inaccuracy of ABPM in patients aged >65 years. Furthermore, day-to-day maximum and CV-SBP were associated with premorbid BP, hypertensive arteriopathy and cardiovascular events, with no additional predictive value of mean SBP when analysed with maximum SBP. Maximum SBP was greater in men and CV-SBP in women, whilst age and creatinine determined both. Increased stroke risk may partly be due to the association between BP variability and cerebral pulsatility, which was correlated with leukoaraiosis (p=0.01) and determined by aortic stiffness (p=0.016) and pulsatility (p<0.001). BP variability is clinically significant and physiologically valid, and is treatable with CCBs and diuretics. After TIA or minor stroke, HBPM best identifies residual hypertension and demonstrates the predictive value of BP variability and maximum BP, but associated arterial changes might explain some of the increased stroke risk.
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Ragoasha, Moagabo Natalie. "The role of short-term atmospheric variability in shaping Lagrangian transport in the Southern Benguela." Master's thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/20006.
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This work studies the links between the Lagrangian transport in the Southern Benguela upwelling system and the ocean circulation through modelling experimentation. More specifically, it intends to show that the wind-induced circulation at short-time scales impacts the drift of Lagrangian particles released in the model. Three ocean model (ROMS) simulations are set-up. Simulation A is forced with a6 hourly atmospheric forcing (surface heat and fresh-water fluxes and wind stress). In simulation B and C, the atmospheric forcing is low-pass filtered with 5 days and 30 days cut-off periods. The ocean model outputs are averaged and saved at deferent temporal frequency: frequencies of 6 hours and 3 days. Particles released in the Lagrangian tracking tool are transported by the velocity vectors produced by the ocean model into the nursery area located at Saint Helena Bay. The presence of short-term fluctuations result in higher inner shelf transport and amore elongated plume dispersion pattern with much refine spatial scales. This finding contrasts with previous studies where the inner shelf transport success was always low compared to the outer shelf nursery. When the high frequency signal is filtered out, the inner shelf transport is greatly reduced especially during the upwelling season. The archiving frequency of the ROMS output is shown to impact Lagrangian studies, especially when the atmospheric forcing has variability at short time scales (less than 5 days).Monthly mean forcing results in dynamics variable with periods of not less than a month and 5 daily averaged forcing with sub-weekly dynamics. Therefore, in simulations B and C the less than 3 days archiving of the model outputs is not necessary, because their forcing does not generate dynamics with such periods. The latter must be adapted so that it does not filter out the ocean response to the high frequency atmospheric forcing. To explain the Lagrangian transports, as a first approach, the transport success was linked to the variability of the ocean circulation.
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Luken, Heather Grace. "Long-term response of zooplankton biomass and phenology to environmental variability in a eutrophic reservoir." Miami University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=miami1605897812690996.
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Grinberg, Victoria Verfasser], and Jörn [Akademischer Betreuer] [Wilms. "Investigations of the long term variability of black hole binaries / Victoria Grinberg. Gutachter: Jörn Wilms." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2014. http://d-nb.info/1054342288/34.
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Canepari, Marco. "Intrinsic variability and short-term changes in synaptic transmission in the rat hippocampal CA3 region." Doctoral thesis, SISSA, 1999. http://hdl.handle.net/20.500.11767/4432.
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Pederson, Gregory Thomas. "Long-term perspectives on Northern Rockies climatic variability from tree rings in Glacier National Park, Montana." Thesis, Montana State University, 2004. http://etd.lib.montana.edu/etd/2004/pederson/PedersonG04.pdf.
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Instrumental climate records reveal fluctuations in summer moisture anomalies and winter snowpack in Glacier National Park, Montana, on decadal and multidecadal timescales. However, because climate records for the region are limited to the 20th century, studies on the impacts of long-duration variations in climate on physical and ecosystem processes were limited. Therefore, a reconstruction of summer moisture variability (June - August) spanning A.D. 1540-2000 was created from a multi-species network of tree-ring chronologies sampled in Glacier National Park. The reconstruction shows decadal-scale shifts between drought and pluvial events with a pronounced cool/wet period spanning the end of the Little Ice Age (A.D. 1770-1840). The single most exceptional drought event occurred over the 20th century (A.D. 1917-1941) and was associated with the most spatially consistent drought regime throughout the northern Rockies and Pacific Northwest over the past ~500 yrs. Among a wider spatial network of hydroclimatic reconstructions arrayed along a north-south Rocky Mountain transect, trends at Glacier National Park were found to be most similar to those in the Canadian Rockies and the Pacific Northwest. Also, many decadal-scale drought/pluvial events were consistent among all sites along the north-south transect - although magnitude, intensity, and time of onset varied. To investigate climatic drivers related to the Little Ice Age glacial maximum and rapid 20th-century retreat, I explored the impact of north Pacific Basin sea-surface temperature anomalies on low-frequency variations in winter snowpack for the park. Temperature anomalies in the north Pacific basin exhibit tight linkages to variations in snowpack; therefore, I used a tree-ring based reconstruction of north Pacific temperature variability and summer drought as proxies for winter glacial accumulation and summer ablation, respectively, over the past three centuries (A.D. 1700-2000). These records show that the 1850's glacial maximum was likely produced by ~70 yrs of cool/wet summers coupled with high snowpack. Glacial retreat coincided with an extended period (>50 yr) of summer drought and low snowpack culminating in the exceptional events of 1917-1941 when retreat rates exceeded 100 m/yr. This research highlights the difficulty in detecting regional expression of global climate change when 'natural' decadal-scale variations in climate are regionally common.
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O'Connor, Eve. "Long-term Spatial and Temporal Variability of Benthic Macroinvertebrate Communities: Implications for Bioassessment of Lotic Systems." VCU Scholars Compass, 2010. http://scholarscompass.vcu.edu/etd/2064.
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The structure and composition of benthic macroinvertebrate communities can vary spatially and over time. Spatial and temporal variation along a stream has many implications for population and community dynamics, which may influence bioassessment programs. I examined variability in the benthic community of eight streams within the Polecat Creek, Virginia watershed. These streams vary in size from 1st to 4th order. The streams were sampled once every season for eleven years using standard bioassessment protocols. Macroinvertebrates were sampled from both sediment and submerged wood habitats at each site. The coefficient of variation (CV) was used to quantify among season, among year and among site variability of eight community metrics from both the sediment and wood samples. ANOVAs were calculated using Tukey post-hoc test to determine if there were statistically significant differences in taxonomic richness and mean CV values across seasons, years and sites for both sediment and wood samples. Sorenson’s Quotient of Similarity was used to examine the extent of differences in the taxonomic composition of the macroinvertebrate communities among the four seasons over the 11 years of the study and among the 8 sampling sites. A high amount of variability was observed among seasons, sites and years. A wide range of CV values was observed among community metrics, with certain metrics exhibiting low overall mean CV values and others exhibiting very high overall mean CV values. It is important to understand the temporal and spatial variability of macroinvertebrates when planning biomonitoring programs.
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Amélineau, Françoise. "Sensibilité d’un oiseau marin arctique aux changements environnementaux." Thesis, Montpellier, 2016. http://www.theses.fr/2016MONTT110/document.
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L’Arctique se réchauffe deux fois plus vite que le reste du monde, entrainant des changements majeurs des écosystèmes marins. Par exemple, l’étendue de la banquise diminue, et la distribution des masses d’air change, modifiant les régimes de vents et de précipitations. Parallèlement à ces changements climatiques, l’Arctique est soumise à une pollution anthropique croissante amenée par les circulations atmosphériques et océaniques, et accentuée par le développement des activités humaines locales. Dans ce contexte, il est urgent de comprendre les impacts écologiques de ces modifications environnementales sur les espèces de cette région. Les mergules nains (Alle alle) sont les oiseaux marins les plus abondants de l’Arctique, et des acteurs clés des réseaux trophiques côtiers. Bien que des travaux récents aient suggéré une forte résilience de ces organismes aux changements globaux, une étude approfondie permettant de comprendre de manière détaillée l’impact de ces changements était essentielle. Au cours de ce travail de thèse, nous avons donc utilisé une approche pluridisciplinaire (écologie alimentaire, écotoxicologie, bioénergétique, écologie du déplacement) menée à long terme afin de caractériser la sensibilité des mergules nains aux changements de leur environnement pendant la saison de reproduction (été) et en hiver. Nous avons pour cela étudié une population de mergules nains au Groenland Est. Nos résultats montrent que les mergules sont fortement impactés par les changements en cours. Pendant la période de reproduction, leurs proies changent et leur effort de plongée augmente en l’absence de banquise, même s’ils demeurent fidèles à leur zone de nourrissage sur le talus continental. Ceci tend à diminuer leur condition corporelle et celle de leur poussin, mais n’impacte pas leur survie. En hiver, les mergules nains optimisent leur migration et leur distribution en fonction de la distribution de leurs proies et de leur paysage énergétique. Ainsi, nos modèles prédictifs indiquent qu’un réchauffement de l’Atlantique nord pourrait être bénéfique pour les populations en diminuant leurs besoins énergétiques. Enfin, nous avons trouvé que les mergules nains consomment des microplastiques, et ce en les confondant avec leurs proies. Cette source de pollution supplémentaire pourrait augmenter avec la fonte de la banquise qui libère des microplastiques jusque-là stockés dans la glace. Ce travail souligne l’importance des programmes à long terme pour l’étude des impacts des changements globaux<br>The Arctic is warming twice faster than the rest of the world, leading to major changes for marine ecosystems. For example, sea-ice extent is decreasing, and air mass distribution is changing, thus modifying wind and precipitation regimes. In parallel, the Arctic is subject to increasing anthropogenic pollution carried by atmospheric and oceanic circulation, and accentuated by the development of local human activities. In this context, there is an urgent need to understand the ecological impacts of these environmental modifications on the species of this region. Little auks (Alle alle) are the most abundant seabird in the Arctic, and key players of coastal food webs. Although recent works suggested a high resiliency of little auks to global changes, a comprehensive study was needed to understand in detail the impacts of these changes. Through this work, we used a multidisciplinary approach (diet ecology, ecotoxicology, bioenergetics, foraging ecology) on the long term to characterize little auk sensitivity to environmental changes during the breeding season (summer) and in winter. We therefore studied a little auk population in East Greenland. Our results show that little auks are indeed impacted by ongoing changes. During the breeding season, their prey change and their diving effort increase when there is no sea-ice, even if they remain faithful to their feeding grounds on the continental slope. This tends to decrease their body condition and that of their chick, but does not impact their survival. In winter, little auks optimize their migration and their distribution according to the distribution of their prey and their energetic landscape. Therefore, our predictive models indicate that a warming of the North Atlantic could be benefic for little auk populations, by reducing their energetic needs. Finally, we found that little auks ingest microplastics, by confusing them with their prey. This additional source of pollution could increase with sea-ice loss that release microplastics stocked in the ice. This work underlines the importance of long term monitoring programs for the study of global change impacts
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Esper, Jan, Edward R. Cook, Paul J. Krusic, Kenneth Peters, and Fritz H. Schweingruber. "Tests of the RCS Method for Preserving Low-Frequency Variability in Long Tree-Ring Chronologies." Tree-Ring Society, 2003. http://hdl.handle.net/10150/262573.
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To preserve multi-centennial length variability in annual tree-ring chronologies, the Regional Curve Standardization (RCS) method calculates anomalies from a regionally common, non-climatic age-trend function. The influence of various factors on the estimation of the regional curve (RC) and resulting RCS- chronology is discussed. These factors are: the method of calculating anomalies from the age-trend function, estimation of the true pith offset, the number of series used, species composition, and site characteristics. By applying RCS to a collection of millennium-length tree-ring data sets, the potential and limitations of the RCS method are investigated. RCS is found to be reasonably robust with respect to tested factors, suggesting the method is a suitable tool for preserving low-frequency variance in long tree-ring chronologies.
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Korhonen, Iikka. "Methods for the analysis of short-term variability of heart rate and blood pressure in frequency domain /." Espoo : Technical Research Centre of Finland, 1997. http://www.vtt.fi/inf/pdf/publications/1997/P316.pdf.
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Verrot, Lucile. "Modeling long-term variability and change of soil moisture and groundwater level - from catchment to global scale." Doctoral thesis, Stockholms universitet, Institutionen för naturgeografi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-128322.
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The water stored in and flowing through the subsurface is fundamental for sustaining human activities and needs, feeding water and its constituents to surface water bodies and supporting the functioning of their ecosystems. Quantifying the changes that affect the subsurface water is crucial for our understanding of its dynamics and changes driven by climate change and other changes in the landscape, such as in land-use and water-use. It is inherently difficult to directly measure soil moisture and groundwater levels over large spatial scales and long times. Models are therefore needed to capture the soil moisture and groundwater level dynamics over such large spatiotemporal scales. This thesis develops a modeling framework that allows for long-term catchment-scale screening of soil moisture and groundwater level changes. The novelty in this development resides in an explicit link drawn between catchment-scale hydroclimatic and soil hydraulics conditions, using observed runoff data as an approximation of soil water flux and accounting for the effects of snow storage-melting dynamics on that flux. Both past and future relative changes can be assessed by use of this modeling framework, with future change projections based on common climate model outputs. By direct model-observation comparison, the thesis shows that the developed modeling framework can reproduce the temporal variability of large-scale changes in soil water storage, as obtained from the GRACE satellite product, for most of 25 large study catchments around the world. Also compared with locally measured soil water content and groundwater level in 10 U.S. catchments, the modeling approach can reasonably well reproduce relative seasonal fluctuations around long-term average values. The developed modeling framework is further used to project soil moisture changes due to expected future climate change for 81 catchments around the world. The future soil moisture changes depend on the considered radiative forcing scenario (RCP) but are overall large for the occurrence frequency of dry and wet events and the inter-annual variability of seasonal soil moisture. These changes tend to be higher for the dry events and the dry season, respectively, than for the corresponding wet quantities, indicating increased drought risk for some parts of the world.
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Dangerfield, C. E. "Stochastic models of ion channel dynamics and their role in short-term repolarisation variability in cardiac cells." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:cd0be850-1ff0-4792-8171-438ff8fc0161.
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Sudden cardiac death due to the development of lethal arrhythmias is the dominant cause of mortality in the UK, yet the mechanisms underlying their onset, maintenance and termination are still poorly understood. Therefore biomarkers are used to determine arrhythmic risk within patients and of new drug compounds. In recent years, the magnitude of variations in the length of successive beats, measured over a short period of time, has been shown to be a powerful predictor of arrhythmic risk. This beat-to-beat variability is thought to be the manifestation of the random opening and closing dynamics of individual ion channels that lie within the membrane of cardiac cells. Computational models have become an important tool in understanding the electrophysiology of the heart. However, current state-of-the-art electrophysiology models do not incorporate this intrinsic stochastic behaviour of ion channels. Those that do use computationally costly methods, restricting their use in complex tissue scale simulations, or employ stochastic simulation methods that result in negative numbers of channels and so are inaccurate. Therefore, using current stochastic modelling techniques to investigate the role of stochastic ion channel behaviour in beat-to-beat variability presents difficulties. In this thesis we take a mathematically rigorous and novel approach to develop accurate and computationally efficient models of stochastic ion channel dynamics that can be incorporated into existing electrophysiology models. Two different models of stochastic ion channel behaviour, both based on a system of stochastic differential equations (SDEs), are developed and compared. The first model is based on an existing SDE model from population dynamics called the Wright-Fisher model. The second approach incorporates boundary conditions into the SDE model of ion channel dynamics that is obtained in the limit from the discrete-state Markov chain model, and is called a reflected SDE. Of these two methods, the reflected SDE is found to more accurately capture the stochastic dynamics of the discrete-stateMarkov chain, seen as the ‘gold-standard’ model and also provides substantial computational speed up. Thus the reflected SDE is an accurate and efficient model of stochastic ion channel dynamics and so allows for detailed investigation into beat-to-beat variability using complex computational electrophysiology models. We illustrate the potential power of this method by incorporating it into a state-of-the-art canine cardiac cell electrophsyiology model so as to explore the effects of stochastic ion channel behaviour on beat-to-beat variability. The stochastic models presented in this thesis fulfil an important role in elucidating the effects of stochastic ion channel behaviour on beat-to-beat variability, a potentially important biomarker of arrhythmic risk.
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Gao, Xiu. "Long-term and seasonal response of rotifer biomass and phenology to environmental variability in a eutrophic reservoir." Miami University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=miami1622278284537733.
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Musat, Ileana Cristina. "Short-term variability of atmospheric extinction during the night, under clear-sky conditions, investigated by broadband stellar photometry." College Park, Md. : University of Maryland, 2004. http://hdl.handle.net/1903/1897.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2004.<br>Thesis research directed by: Meteorology. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Walliser, Eric Otto [Verfasser]. "The short-term climate variability of shallow marine environments in Central Europe during the Oligocene / Eric Otto Walliser." Mainz : Universitätsbibliothek Mainz, 2017. http://d-nb.info/1128339188/34.
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Lerner, Harry Joseph. "Lithic raw material variability and the reduction of short-term use implements : an example from Northwestern New Mexico." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=102675.
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Chipped stone tools are a truly dynamic medium of material culture. From initial reduction to contemporary excavation, lithic artifacts undergo continuous change. The role of the properties of raw materials in determining rates of use-wear accrual is poorly understood and has rarely been assessed quantitatively (e.g. Goodman, 1944; Greiser and Sheets, 1979; McDevitt, 1994). This dissertation offers such quantification regarding four materials exploited for the production of short-term use implements at the Late Archaic FA2-13 site located just outside the city of Farmington, New Mexico.<br>Both experimental and archaeological use-wear evidence was assessed in separate but related ways. Digital image analysis of use-wear invasiveness using ClemexVision PE and GIS analysis of use-wear homogeneity using Idrisi Kilimanjaro yielded distinct but highly complementary results. Direct testing of material properties of non-archaeological samples using a Hysitron Triboindenter served to further clarify these findings in terms of the complex relationship between raw material surface hardness and roughness.<br>The results of the present study show that there are significant differences between rates of wear accrual among the four materials. Analysis of tools from FA2-13 indicates that while scraping activities likely did predominate (Schutt, 1997a), it may also be feasible to generate more detailed assessments regarding the kinds of scraping activities that were undertaken and the respective intensities with which they were performed. This increased insight can then be extrapolated for application to long-term use technologies and their more complex life histories.
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Benlloch, García Sara [Verfasser]. "Long-term X-ray variability of active galactic nuclei and X-ray binaries / vorgelegt von Sara Benlloch García." [Tübingen] : S. Benlloch García, 2004. http://d-nb.info/970655045/34.
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Brun, Caroline Elisabeth Hénia. "Economic and technical impacts of wind variability and intermittency on long-term generation expansion planning in the U.S." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/65499.
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Thesis (S.M. in Technology and Policy)--Massachusetts Institute of Technology, Engineering Systems Division, Technology and Policy Program, 2011.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (p. 57-59).<br>Electricity power systems are a major source of carbon dioxide emissions and are thus required to change dramatically under climate policy. Large-scale deployment of wind power has emerged as one key driver of the shift from conventional fossil-fuels to renewable sources. However, technical and economic concerns are arising about the integration of variable and intermittent electricity generation technologies into the power grid. Designing optimal future power systems requires assessing real wind power capacity value as well as back-up costs. This thesis develops a static cost-minimizing generation capacity expansion model and applies it to a simplified representation of the U.S. I aggregate an hourly dataset of load and wind resource in eleven regions in order to capture the geographical diversity of the U.S. Sensitivity of the optimal generation mix over a long-term horizon with respect to different cost assumptions and policy scenarios is examined. I find that load and wind resource are negatively correlated in most U.S. regions. Under current fuel costs (average U.S. costs for year 2002 to year 2006) regional penetration of wind ranged from 0% (in the South East, Texas and South Central regions) to 22% (in the Pacific region). Under higher fuel costs as projected by the Energy Information Administration (average for the period of 2015 to 2035) penetration ranged from 0.3% (in the South East region) to 59.7% (in the North Central region). Addition of a C02 tax leads to an increase of optimal wind power penetration. Natural gas-fired units are operating with an actual capacity factor of 17% under current fuel costs and serve as back-up units to cope with load and wind resource variability. The back-up required to deal specifically with wind resource variations ranges from 0.25 to 0.51 MW of natural gas-fired installed per MW of wind power installed and represents a cost of $4/MWh on average in the U.S., under current fuel costs.<br>by Caroline Elisabeth Hénia Brun.<br>S.M.in Technology and Policy
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Traube, Joshua White. "Predicting the Effects of Short-Term Photovoltaic Variability on Power System Frequency for Systems with Integrated Energy Storage." Thesis, University of Colorado at Boulder, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3607371.
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<p> The percentage of electricity supplied by photovoltaic (PV) generators is steadily rising in power systems worldwide. This rise in PV penetration may lead to larger fluctuations in power system frequency due to variability in PV generator output at time scales that fall between the inertial damping and automatic generation control (AGC) responses of power systems. To reduce PV generator variability, active power controls can be implemented in the power electronic inverters that interface PV generators to the power system. Although various types of active power controls have been developed, no standard methodology exists for evaluating the effectiveness of these controls at improving power system frequency regulation. This dissertation presents a method for predicting the effects of short-term PV variability on power system frequency for a PV generator with active power control provided by integrated energy storage. A custom model of a PV generator with integrated energy storage is implemented in a power system dynamic simulator and validated through experiments with a grid emulator. The model is used to predict the effects of short-term PV variability on the frequency of the IEEE 9-bus test power system modified to include a PV generator with integrated energy storage. In addition, this dissertation utilizes linear analysis of power system frequency control to predict worst-case frequency deviations as a function of the amount of energy storage integrated into PV generators. Through simulation and emulation on a scaled experimental prototype, the maximum frequency deviation caused by the PV generator with a small amount of integrated energy storage is found to be approximately 33% lower than the maximum frequency deviation caused by the PV generator alone. Through linear analysis it is shown that by adding only 36.7 kWh of integrated energy storage to a 1.2 MW PV system, the worst-case frequency deviation on the IEEE 9-bus test system can be reduced 65% from 0.45 Hz to 0.16 Hz. The techniques presented enable estimation of the maximum PV penetration or minimum integrated energy storage requirement to meet a frequency regulation target for a particular power system. Integrated energy storage can then be compared to other active power controls in order to choose a method that meets frequency control requirements at minimum cost.</p>
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Davies, Sarah B. "Vegetation Dynamics of a Tidal Freshwater Marsh: Long-Term and Inter-Annual Variability and their Relationship to Salinity." W&M ScholarWorks, 2004. https://scholarworks.wm.edu/etd/1539617817.
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Reins, Nina J. "Long Term Bathymetry Changes in the Lower Mississippi River due to Variability in Hydrograph and Variable Diversion Schemes." ScholarWorks@UNO, 2018. https://scholarworks.uno.edu/td/2490.
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This research is part of an ongoing effort to improve predictions for bathymetric and morphological changes in the Lower Mississippi River. The utilized model is a subset of a previously calibrated Delft3D model. This shorter model has reduced computational time, and can be deployed for analysis focused on the area between Belle Chasse and HOP, which is the domain of the model. Simulation runs conducted under this study vary from 12 years to 48 years, utilizing a developed 12-year variable hydrograph.
The comparison of variable annual hydrograph and repeated representative annual (uniform) hydrograph input data on bathymetric changes indicated that the absolute bathymetric equilibrium is dependent on year to year variability. The utilization of a uniform hydrograph increases the predicted deposition within the river domain. When evaluating diversion sand capture, utilizing a uniform hydrograph can be considered a conservative approach, while utilizing a variable hydrograph will result in more accurate sand load volumes captured by the diversion.In general, sediment capture showed only minor interdependencies amongst multiple diversions, as long as the total diversion flow is less than 140,000cfs.
This study shows that morphological changes are dependent on the number and location of multiple diversions. The largest interdependencies occur for the most downstream diversions, which increase with the total diverted flow. A true equilibrium was not achieved within 48 years, with or without sea level rise. It was observed, that the system with diversions responds to sea level rise by an increase in deposition, which increases with total diverted flow.
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Fitiwi, Desta Zahlay. "Strategies, Methods and Tools for Solving Long-term Transmission Expansion Planning in Large-scale Power Systems." Doctoral thesis, KTH, Skolan för elektro- och systemteknik (EES), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-192363.
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Driven by a number of factors, the electric power industry is expected to undergo a paradigm shift with a considerably increased level of variable energy sources. A significant integration of such sources requires heavy transmission investments over geographically wide and large-scale networks. However, the stochastic nature of such sources, along with the sheer size of network systems, results in problems that may become intractable. Thus, the challenge addressed in this work is to design efficient and reasonably accurate models, strategies and tools that can solve large-scale TEP problems under uncertainty. A long-term stochastic network planning tool is developed, considering a multi-stage decision framework and a high level integration of renewables. Such a tool combines the need for short-term decisions with the evaluation of long-term scenarios, which is the practical essence of a real-world planning. Furthermore, in order to significantly reduce the combinatorial solution search space, a specific heuristic solution strategy is devised. This works by decomposing the original problem into successive optimization phases.One of the modeling challenges addressed in this work is to select the right network model for power flow and congestion evaluation: complex enough to capture the relevant features but simple enough to be computationally fast. Another relevant contribution is a domain-driven clustering process of snapshots which is based on a “moments” technique. Finally, the developed models, methods and solution strategies have been tested on standard and real-life systems. This thesis also presents numerical results of an aggregated 1060-node European network system considering multiple RES development scenarios. Generally, test results show the effectiveness of the proposed TEP model, since—as originally intended—it contributes to a significant reduction in computational effort while fairly maintaining optimality of the solutions.<br>Driven by several techno-economic, environmental and structural factors, the electric energy industry is expected to undergo a paradigm shift with a considerably increased level of renewables (mainly variable energy sources such as wind and solar), gradually replacing conventional power production sources. The scale and the speed of integrating such sources of energy are of paramount importance to effectively address a multitude of global and local concerns such as climate change, sustainability and energy security. In recent years, wind and solar power have been attracting large-scale investments in many countries, especially in Europe. The favorable agreements of states to curb greenhouse gas emissions and mitigate climate change, along with other driving factors, will further accelerate the renewable integration in power systems. Renewable energy sources (RESs), wind and solar in particular, are abundant almost everywhere, although their energy intensities differ very much from one place to another. Because of this, a significant integration of such energy sources requires heavy investments in transmission infrastructures. In other words, transmission expansion planning (TEP) has to be carried out in geographically wide and large-scale networks. This helps to effectively accommodate the RESs and optimally exploit their benefits while minimizing their side effects. However, the uncertain nature of most of the renewable sources, along with the size of the network systems, results in optimization problems that may become intractable in practice or require a huge computational effort. Thus, the challenge addressed in this work is to design models, strategies and tools that may solve large-scale and uncertain TEP problems, being computationally efficient and reasonably accurate. Of course, the specific definition of the term “reasonably accurate” is the key issue of the thesis work, since it requires a deep understanding of the main cost and technical drivers of adequate TEP investment decisions. A new formulation is proposed in this dissertation for a long-term planning of transmission investments under uncertainty, with a multi-stage decision framework and considering a high level of renewable sources integration. This multi-stage strategy combines the need for short-term decisions with the evaluation of long-term scenarios, which is the practical essence of a real-world planning. The TEP problem is defined as a stochastic mixed-integer linear programming (S-MILP) optimization, an exact solution method. This allows the use of effective off-the-shelf solvers to obtain solutions within a reasonable computational time, enhancing overall problem tractability. Furthermore, in order to significantly reduce the combinatorial solution search (CSS) space, a specific heuristic solution strategy is devised. In this global heuristic strategy, the problem is decomposed into successive optimization phases. Each phase uses more complex optimization models than the previous one, and uses the results of the previous phase so that the combinatorial solution search space is reduced after each phase. Moreover, each optimization phase is defined and solved as an independent problem; thus, allowing the use of specific decomposition techniques, or parallel computation when possible. A relevant feature of the solution strategy is that it combines deterministic and stochastic modeling techniques on a multi-stage modeling framework with a rolling-window planning concept. The planning horizon is divided into two sub-horizons: medium- and long-term, both having multiple decision stages. The first sub-horizon is characterized by a set of investments, which are good enough for all scenarios, in each stage while scenario-dependent decisions are made in the second sub-horizon. One of the first modeling challenges of this work is to select the right network model for power flow and congestion evaluation: complex enough to capture the relevant features but simple enough to be computationally fast. The thesis includes extensive analysis of existing and improved network models such as AC, linearized AC, “DC”, hybrid and pipeline models, both for the existing and the candidate lines. Finally, a DC network model is proposed as the most suitable option. This work also analyzes alternative losses models. Some of them are already available and others are proposed as original contributions of the thesis. These models are evaluated in the context of the target problem, i.e., in finding the right balance between accuracy and computational effort in a large-scale TEP problem subject to significant RES integration. It has to be pointed out that, although losses are usually neglected in TEP studies because of computational limitations, they are critical in network expansion decisions. In fact, using inadequate models may lead not only to cost-estimation errors, but also to technical errors such as the so-called “artificial losses”. Another relevant contribution of this work is a domain-driven clustering process to handle operational states. This allows a more compact and efficient representation of uncertainty with little loss of accuracy. This is relevant because, together with electricity demand and other traditional sources of uncertainty, the integration of variable energy sources introduces an additional operational variability and uncertainty. A substantial part of this uncertainty and variability is often handled by a set of operational states, here referred to as “snapshots”, which are generation-demand patterns of power systems that lead to optimal power flow (OPF) patterns in the transmission network. A large set of snapshots, each one with an estimated probability, is then used to evaluate and optimize the network expansion. In a long-term TEP problem of large networks, the number of operational states must be reduced. Hence, from a methodological perspective, this thesis shows how the snapshot reduction can be achieved by means of clustering, without relevant loss of accuracy, provided that a good selection of classification variables is used in the clustering process. The proposed method relies on two ideas. First, the snapshots are characterized by their OPF patterns (the effects) instead of the generation-demand patterns (the causes). This is simply because the network expansion is the target problem, and losses and congestions are the drivers to network investments. Second, the OPF patterns are classified using a “moments” technique, a well-known approach in Optical Pattern Recognition problems. The developed models, methods and solution strategies have been tested on small-, medium- and large-scale network systems. This thesis also presents numerical results of an aggregated 1060-node European network system obtained considering multiple RES development scenarios. Generally, test results show the effectiveness of the proposed TEP model, since—as originally intended—it contributes to a significant reduction in computational effort while fairly maintaining optimality of the solutions.<br><p>QC 20160919</p>
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CRESPI, ALICE. "PRECIPITATION CLIMATOLOGIES AND LONG-TERM RECORD RECONSTRUCTION: STUDIES IN A CHANGING CLIMATE." Doctoral thesis, Università degli Studi di Milano, 2019. http://hdl.handle.net/2434/614284.
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The availability of high-resolution datasets describing the spatio-temporal evolution of precipitation is becoming increasingly important in order to analyse the long-term variability and trends of the climatic signal and possible impacts over specific areas of interest. These datasets are therefore crucial not only for research purposes, but also for decision-makers in a wide range of fields, such as agriculture, energy production, hydrology, natural risk monitoring and resource management. The reconstruction of high-resolution climate descriptions requires both accurate in-situ observations and suitable interpolation schemes to project the station data onto regular grids.
The study focuses on the development and improvement of interpolation methods for monthly precipitation data and on the reconstruction and analysis of gridded datasets from dense and high-quality rain-gauge records covering specific study domains.
The first goal of the work was the reconstruction of the high-resolution monthly precipitation climatologies over Italy for the 1961-1990 period. The observation database was set up thanks to a relevant effort of data rescue and collection from a great number of national and international sources and led to more than 4500 quality-checked monthly records available for the climatological reconstruction. Considering the heterogeneous Italian orography and the influence of surface features on precipitation distribution, a local weighted linear regression (LWLR) of precipitation versus elevation was applied to interpolate the station monthly normals onto a 30-arc second resolution Digital Elevation Model (DEM). Leave-one-out (LOO) validation and inter-comparison proved that the approaches modelling the local precipitation-orography relationship provide more accurate results in respect with methods considering larger spatial scales or not including the topography at all. The computed 30-arc second resolution monthly precipitation climatologies for Italy were on-line released and they represent an updated and highly detailed description of precipitation normal over the whole national territory in digital form.
In order to evaluate the temporal evolution of precipitation over some of the most vulnerable Italian regions, gridded datasets of long-term precipitation series were produced by means of the anomaly-based approach. The secular precipitation series were reconstructed for the upper part of Adda river basin (Central Italian Alps), with an additional focus over the Forni glacier, and for Sardinia, as case-study for the Mediterranean area. New records were collected, especially thanks to the integration of the recent automatic station records with those of the previous mechanical networks and to digitisation activities of the most ancient data from hardcopy archives. All the series underwent statistical procedures aiming at avoiding inhomogeneities due to non-climatic signals. The gridded dataset allowed to get the secular areal precipitation records for the study regions and to evaluate their trends. As regards the Adda basin, the reconstructed 1800-2016 series showed statistically significant negative trends for annual and autumn precipitation. The comparison with the 1845-2016 annual basin runoff record, which is one of the longest runoff series available in Italy, allowed both to depict a strong decrease in annual runoff driven by the increase of evapotranspiration and to evaluate the possible contribution of gauge undercatch, especially in mountainous sites, to the underestimation of basin precipitation.
The trend analysis over the 1922-2011 areal monthly precipitation record computed for Sardinia highlighted statistically significant decreases of -2.3% and -4.1% decade-1 in annual and winter values, respectively, and a positive but not statistically significant trend in summer precipitation. These outcomes agreed with other literature studies focusing on precipitation variability over Mediterranean area.
The final part of the work focused on the development of interpolation schemes to improve the accuracy of gridded precipitation fields for domains unevenly covered by station networks. Norway represents a very interesting case-study, where the severe climatic conditions and the complex orography limit the management of in-situ observations over the most remote regions leading to an unbalanced station distribution between North and South and between low and high elevation. At this aim, a new method to compute the Norwegian monthly precipitation climatologies (1981-2010) at 1 km resolution was implemented and the gridded dataset was on-line released for both research and operative purposes. In this scheme, named HCLIM+RK, the HCLIM-AROME climate numerical model fields, which are not based on rain-gauge data and describe the precipitation gradients also over unsampled areas, are combined with available in-situ observations by the kriging interpolation of station residuals. In HCLIM+RK the high-resolution reliable precipitation patterns provided by the numerical model are retained and the station data are used to correct the biases affecting the numerical fields. The LOO reconstruction errors of Norwegian station normal showed that the combined approach almost removes the biases affecting the original HCLIM-AROME dataset and it provides much lower errors than conventional interpolation procedures based on stations only.
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Podritske, Brandi. "Holocene climate variability and long-term diatom community dynamics in a small lake on Victoria Island, Northwest Territory, Canada." Thesis, University of Ottawa (Canada), 2006. http://hdl.handle.net/10393/27407.
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A lake sediment core spanning 9900 years, collected from a small lake on western Victoria Island, provides a high-resolution record of diatom community dynamics over the Holocene. Ten radiocarbon dates and 210Pb dating provided the core chronology. Loss-on-ignition (LOI) gradually increased over the Holocene whereas carbonate content and magnetic susceptibility showed an inverse trend. Biogenic silica content had apparent cyclicity over ~1500 year periods. Major shifts in diatom assemblages at 8100-8000 calendar years before present (cal yrs BP), 5800-5700 cal yrs BP, and 3800-3500 cal yrs BP occurred simultaneously with millennial-scale climate changes reported from the region. There is evidence of diatom community response to centennial scale variations such as the 'Medieval Warm Period' (~1000-700 calendar years before present, cal yrs BP), 'Little Ice Age' (~800-150 cal yrs BP) and recent warming. Variations of the taxa within the genera Staurosira, Pseudostaurosira, Fragilaria, and Staurosirella, usually combined into one genus in Arctic lake sediment studies, suggest these taxa may be more useful in paleolimnological studies than previously believed. Although recent changes in diatom community composition, production and species richness were apparent they were surpassed at other periods throughout the Holocene. The rate of community compositional change in the last few centuries was rapid, however it was not exceptional in the lake history.