Dissertations / Theses: 'Annual variability'

1

Wallace, Craig. "Variability in the annual cycle of temperature and the atmospheric circulation." Thesis, University of East Anglia, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399842.

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2

Gutzler, David Scott. "The structure of annual and interannual wind variability in the tropics." Thesis, Massachusetts Institute of Technology, 1986. http://hdl.handle.net/1721.1/54309.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1986.
Microfiche copy available in Archives and Science
Bibliography: leaves 218-224.
by David Scott Gutzler.
Ph.D.

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3

Ding, Hui [Verfasser]. "Annual to interannual equatorial Atlantic variability : mechanisms and tropical impacts / Hui Ding." Kiel : Universitätsbibliothek Kiel, 2010. http://d-nb.info/1020003529/34.

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4

Hytteborn, Julia. "Water Quality in Swedish Lakes and Watercourses : Modeling the Intra-Annual Variability." Doctoral thesis, Uppsala universitet, Institutionen för geovetenskaper, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-234480.

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Water quality is of great importance for ecosystems and society. This thesis characterized and modeled the variation in several key constituents of Swedish surface waters, with particular consideration given to intra-annual variability and sensitivity to climate change. Cyanobacterial data from 29 lakes and basins as well as total organic carbon (TOC) from 215 watercourses were used. Extensive data on catchment characteristics, morphometry, discharge, temperature and other water chemistry data were also analyzed. Models characterizing the seasonality in cyanobacterial concentration and relative cyanobacterial abundance were developed with common lake variables. Concentrations of TOC, iron and absorbance were simulated using discharge, seasonality and long-term trend terms in the Fluxmaster modeling system. Spatial patterns in these model terms were investigated, and the sensitivity of cyanobacteria and TOC to future climate was explored. Nutrients were the major control on cyanobacterial concentration seasonality, while temperature was more important for relative cyanobacterial abundance. No cyanobacterial blooms occurred below a total phosphorus threshold of 20 µg l-1. Discharge and seasonality explained much of the intra-annual variability in TOC, but catchment characteristics could only explain a limited amount of the spatial patterns in the sensitivity to these influences. North of Limes Norrlandicus the discharge term had a larger impact on the TOC concentration in large catchments than in small catchments, while south of Limes Norrlandicus the seasonality had a larger impact in small catchments than in larger catchments. According to the climate change scenarios, both TOC and cyanobacterial concentrations will be higher in the future. The cyanobacterial dominance will start earlier and persist longer. The spring TOC concentration peak will come earlier. The changes in TOC loads are more uncertain due to predicted declines in discharge. Parsimonious statistical regression models could explain observed variability in cyanobacteria and TOC. For predictions, these models assume that future aquatic ecosystems will exhibit the same sensitivity to major drivers as in the past. If this proves not to be the case, the modeling can serve as a sentinel for changing catchment function as indicated by degradation in model performance when calibrations on older data are used to model later observations.

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5

Filipe, Vianda Lulendo Luankosi. "Seasonal and inter-annual variability of SST and chlorophyll-a off Angola." Master's thesis, University of Cape Town, 2006. http://hdl.handle.net/11427/6472.

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Includes bibliographical references (p. 105-112).
The aim of this dissertation is to use satellite-derived images for the study of spatial and temporal variations in SST and in concentration of surface chlorophyll-a of the main oceanographic features off Angola. SST time-series over the 1987 to 2002 were derived from Meteosat 5-day SST composites with a spatial resolution of about 5-6 km in Angolan waters and a thermal resolution of 0.5°C. Chlorophyll-a data were from a 5-day composite of SeaWiFS GAC (4.5 km 'Global Area Coverage') images. Such images were available on a format comparable with the Meteosat SST composite images and covered the period 1998 to 2004.

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6

Mount, Christopher P. "Spatial, temporal, and inter-annual variability of the Martian northern seasonal polar cap." Thesis, Northern Arizona University, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=1537795.

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Earth and Mars have nearly the same axial tilt, so seasons on these two bodies progress in a similar manner. During fall and winter on Mars, the primarily CO₂ atmosphere (~95% by volume) condenses out onto the poles as ice. Approximately 25% of the entire Martian atmosphere condenses, and then sublimes in the spring, making this cycle a dominant driver in the global climate. Because the water and dust cycles are coupled to this CO₂ cycle, we must examine seasonal CO₂ processes to understand the global (seasonal) distribution of H₂O on Mars. The density of the ice may indicate whether it condensed in the atmosphere and precipitated as “snow” or condensed directly onto the surface as “slab”. Variations in density may be controlled by geographic location and surface morphology. The distribution and variations in densities of seasonal deposits on the Martian poles gives us insight to the planet’s volatile inventories. Here we analyze density variations over time on Mars’ Northern Polar Seasonal Cap (NPSC) using observational data and energy balance techniques.

We calculate the bulk density of surface CO₂ ice by dividing the column mass abundance (the mass of CO₂ per unit area) by the depth of the ice cap at a given location. We use seasonal rock shadow measurements from High Resolution Imaging Science Experiment (HiRISE) images to estimate ice depth. The length of a rock’s shadow is related to its height through the solar incidence angle and the slope of the ground.

From differences in the height of a rock measured in icy vs. ice-free images, we estimate the depth of surface ice at the time of the icy observation. Averaging over many rocks in a region yields the ice depth for that region. This technique yields minimums for ice depth and therefore maximums for density.

Thermal properties of rocks may play an important role in observed ice depths. Crowns of ice may form on the tops of rocks with insufficient heat capacity to inhibit ice condensation, and may cause an artificial increase in shadow length. This increases the apparent height of a rock and thus decreases the apparent surface ice depth. Additionally, moats may form around rocks with sufficient heat capacity to sublime ice as it is deposited. Moating will also artificially increase the shadow lengths (decreasing apparent surface ice depth). We correct for these effects in our depth-estimation technique.

We balance incoming solar flux with outgoing thermal radiation from Thermal Emission Spectrometer (TES) observations to calculate the column mass abundance. TES thermal bolometer atmospheric albedo and temperature observations are a good proxy to the surface bond albedo and effective surface temperature. These parameters are needed to balance the incoming and outgoing flux.

Mars’ atmosphere is tenuous so we assume homogeneous radiance from the surface to the top of the atmosphere, no lateral diffusion of heat, and that any excess heat goes into subliming surface ice in our flux balance. Using a Monte Carlo model, we integrate the net flux until reaching the time where Cap Recession Observations indicate CO₂ has Ultimately Sublimed (the CROCUS date) to obtain the column mass abundance.

We study seasonal ice at three distinct geomorphic units: plains, dune fields, and craters. Two plains regions, four dunes regions, and two crater regions are analyzed over springtime sublimation. Data for these regions spanned three Mars Years.

Our results indicate that the evolution of seasonally deposited CO₂ ice on the Northern Polar Cap of Mars is highly dependent on complex relationships between various processes. The grain size, dust contamination, water doping, and density vary dramatically over time. The initially deposited material varies according to local geomorphic features and topography, as well as latitude and longitude. The inter-annual variability of ice may play a role in its evolution over sublimation, but likely plays a smaller role than anticipated. Low normalized initial and time-averaged densities suggest that NPSC deposits are initially low and remain relatively low throughout spring. These densities are very similar to estimates made by previous studies. Thus, we conclude that the NPSC is indeed pervaded by low density deposits. These deposits densify over time, but rarely reach typical characteristics for pure slab ice.

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7

Marston, Michael Lee. "Analysis of Extreme Reversals in Seasonal and Annual Precipitation Anomalies Across the United States, 1895-2014." Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/71697.

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As population and urbanization increase across the United States, the effects of natural hazards may well increase, as extreme events would increasingly affect concentrated populations and the infrastructure upon which they rely. Extreme precipitation is one natural hazard that could stress concentrated populations, and climate change research is engaging heavy precipitation frequency and its impacts. This research focuses on the less-studied phenomenon of an extreme precipitation reversal - defined as an unusually wet (dry) period that is preceded by an unusually dry (wet) period. The magnitude is expressed as the difference in the percentiles of the consecutive periods analyzed. This concept has been documented only once before in a study that analyzed extreme precipitation reversals for a region within the southwestern United States. That study found that large differences in precipitation from consecutive winters, a hydrologically critical season for the region, occurred more frequently than what would be expected from random chance, and that extreme precipitation reversals have increased significantly since 1960. This research expands upon the previous work by extending the analysis to the entire continental United States and by including multiple temporal resolutions. Climate division data were used to determine seasonal and annual precipitation for each of nine climate regions of the continental United States from 1895-2014. Precipitation values were then ranked and given percentiles for seasonal and annual data. The season-to-season analysis was performed in two ways. The first examined consecutive seasons (e.g., winter–spring, spring–summer) while the second analyzed the seasonal data from consecutive years (e.g., spring 2014–spring 2015). The annual data represented precipitation for the period October 1–September 30, or the 'water year' used by water resource managers. Following the approach of the previous study, a secondary objective of the research was to examine large-scale climate teleconnections for historical relationships with the occurrence of precipitation reversals. The El Nino-Southern Oscillation was chosen for analysis due to its well-known relationships with precipitation patterns across the United States. Results indicate regional expressions of a propensity for extreme precipitation reversals and relationships with teleconnections that may afford stakeholders guidance for proactive management. Precipitation reversal (PR) and extreme precipitation reversal (EPR) values were significantly larger for the second half of the study period for the western United States for the winter-to-winter, spring-to-spring, and year-to-year analyses. The fall-to-fall analysis also revealed changes in PR/EPR values for several regions, including the northwest, the Northern Rockies and Plains, and the Ohio Valley. Relationships between the winter-to-winter PR time series and an index representing the El Nino-Southern Oscillation (ENSO) phenomenon were examined. The winter-to-winter PR time series of the Northern Rockies and Plains region and the South exhibited significant relationships with the time series of Niño 3.4 values. El Niño (La Niña) coincided with more wet-to-dry (dry-to-wet) PR/EPR values for the Northern Rockies and Plains, while El Niño (La Niña) coincided with more dry-to-wet (wet-to-dry) PR/EPR values for the South.
Master of Science

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8

Kohn, Deborah Diane. "Effects of genetic variability and founder number in small populations of an annual plant." Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286448.

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9

Bathke, Deborah J. "Meteorological processes controlling the variability of net annual accumulation over the Greenland ice sheet." Connect to this title online, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1073073721.

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Thesis (Ph. D.)--Ohio State University, 2004.
Title from first page of PDF file. Document formatted into pages; contains xv, 200 p.; also includes graphics. Includes bibliographical references (p. 173-184).

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10

Maldonado, Tito. "Inter-annual variability of rainfall in Central America : Connection with global and regional climate modulators." Doctoral thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-304656.

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Central America is a region regularly affected by natural disasters, with most of them having a hydro-meteorological origin. Therefore, the understanding of annual changes of precipitation upon the region is relevant for planning and mitigation of natural disasters. This thesis focuses on studying the precipitation variability at annual scales in Central America within the framework of the Swedish Centre for Natural Disaster Science. The aims of this thesis are: i) to establish the main climate variability sources during the boreal winter, spring and summer by using different statistical techniques, and ii) to study the connection of sea surface temperature anomalies of the neighbouring oceans with extreme precipitation events in the region. Composites analysis is used to establish the variability sources during winter. Canonical correlation analysis is employed to explore the connection between the SST anomalies and extreme rainfall events during May-June and August-October. In addition, a global circulation model is used to replicate the results found with canonical correlation analysis, but also to study the relationship between the Caribbean Sea surface temperature and the Caribbean low-level jet. The results show that during winter both El Niño Southern Oscillation and the Pacific Decadal Oscillation, are associated with changes of the sea level pressure near the North Atlantic Subtropical High and the Aleutian low. In addition, the El Niño Southern Oscillation signal is intensified (destroyed) when El Niño and the Pacific Decadal Oscillation have the same (opposite) sign. Sea surface temperature anomalies have been related to changes in both the amount and temporal distribution of rainfall. Precipitation anomalies during May-June are associated with sea surface temperature anomalies over the Tropical North Atlantic region. Whereas, precipitation anomalies during August-September-October are associated with the sea surface temperature anomalies contrast between the Pacific Ocean and the Tropical North Atlantic region. Model outputs show no association between sea surface temperature gradients and the Caribbean low-level jet intensification. Canonical correlation analysis shows potential for prediction of extreme precipitation events, however, forecast validation shows that socio-economic variables must be included for more comprehensive natural disaster assessments.

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11

Gonçalves, Renata Isabel de Sousa. "Growth variability of Greenlandic cod (Gadus morhua L.) estimated by means of otolith annual increments." Master's thesis, Instituto de Ciências Biomédicas Abel Salazar, 2008. http://hdl.handle.net/10216/9326.

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12

Oozeeraully, Yuneeda Bibi Naheed. "The inter-annual variability in the onset of the enhanced chlorophyll-a east of Madagascar." Master's thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/15686.

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Chlorophyll-a concentration is a measure of phytoplankton biomass and is therefore used as a proxy for primary production. The chlorophyll bloom occurring in the South western Indian Ocean is one of the major blooms in the open ocean and is subject to controversies about its formation, propagation and termination mechanisms. In this study, the region was divided into two sub-regions, the South East region (48°E-66°E, 24°S-30°S) and the East region (70°E-88°E, 24°S-30°S) and satellite datasets of chlorophyll-a, sea surface temperature, wind speed and direction and sea surface height were analysed. A bloom was characterized by twice the mean level of the sub-region (~0.08mg/m3) and three bloom years were identified: 2004, 2006 and 2008. The timing, propagation and termination of the bloom showed spatial and temporal variability. The wavelet analysis revealed a semi-annual signal for 2006 and 2008 and an annual one in 2004 due to the gradual decline in the concentration of chlorophyll-a. The transport of the bloom is affected by the passage of eddies where the concentration of chlorophyll-a is higher in the core and around the edges in cyclonic and anticyclonic eddies respectively. The bloom could be present at the sub-surface level throughout the years but is only apparent at the surface during specific years.

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13

Switanek, Matthew. "Improving Seasonal to Annual Predictions of Climate Variability and Water Availability at the Catchment Scale." Thesis, The University of Arizona, 2008. http://hdl.handle.net/10150/193313.

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In a water-stressed region, such as the southwestern United States, it is essential to improve current seasonal hydroclimatic predictions. Typically, seasonal hydroclimatic predictions have been conditioned by standard climate indices, e.g., NINO3 and PDO. In this work, a methodology called basin-specific climate prediction (BSCP) is proposed to improve hydroclimatic predictions. The method analyzes the statistically unique relationships between sea surface temperatures (SSTs) and a basin's hydroclimate. The oceanic region which maximizes the correlation is subsequently used as a predictor for hydroclimate. BSCP is used to perform hindcasts for the hydroclimate in the Little Colorado River basin and the results are compared to those using standard climate indices as predictors.

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Gonçalves, Renata Isabel de Sousa. "Growth variability of Greenlandic cod (Gadus morhua L.) estimated by means of otolith annual increments." Dissertação, Instituto de Ciências Biomédicas Abel Salazar, 2008. http://hdl.handle.net/10216/9326.

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15

White, Kellie L. "Annual and intra-annual shell growth lines of the freshwater bivalve Pyganodon grandis, an evaluation of their utility for the analysis of past environmental variability." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/mq30853.pdf.

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16

Köchy, Martin. "Opposite trends in life stages of annual plants caused by daily rainfall variability : interaction with climate change." Universität Potsdam, 2006. http://opus.kobv.de/ubp/volltexte/2007/1469/.

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Global Circulation Models of climate predict not only a change of annual precipitation amounts but also a shift in the daily distribution. To improve the understanding of the importance of daily rain pattern for annual plant communities, which represent a large portion of semi-natural vegetation in the Middle East, I used a detailed, spatially explicit model. The model explicitly considers water storage in the soil and has been parameterized and validated with data collected in field experiments in Israel and data from the literature. I manipulated daily rainfall variability by increasing the mean daily rain intensity on rainy days (MDI, rain volume/day) and decreasing intervals between rainy days while keeping the mean annual amount constant. In factorial combination, I also increased mean annual precipitation (MAP). I considered five climatic regions characterized by 100, 300, 450, 600, and 800 mm MAP. Increasing MDI decreased establishment when MAP was >250 mm but increased establishment at more arid sites. The negative effect of increasing MDI was compensated by increasing mortality with increasing MDI in dry and typical Mediterranean regions (c. 360–720 mm MAP). These effects were strongly tied to water availability in upper and lower soil layers and modified by competition among seedlings and adults. Increasing MAP generally increased water availability, establishment, and density. The order of magnitudes of MDI and MAP effects overlapped partially so that their combined effect is important for projections of climate change effects on annual vegetation. The effect size of MAP and MDI followed a sigmoid curve along the MAP gradient indicating that the semi-arid region (≈300 mm MAP) is the most sensitive to precipitation change with regard to annual communitie

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Marble, Douglas Craig. "Simulated annual and seasonal Arctic Ocean and sea-ice variability from a high resolution, coupled ice-ocean model." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2001. http://handle.dtic.mil/100.2/ADA397317.

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Dissertation (Ph.D. in Physical Oceanography) Naval Postgraduate School, Sept. 2001.
Dissertation supervisors: Maslowski, Wieslaw ; Semtner, Albert J. "September 2001." Includes bibliographical references (p. 163-177). Also available online.

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18

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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19

Chiarini, Francesca <1983&gt. "Study of the inter-annual variability of particle vertical fluxes in two moorings in the Ross Sea (Antarctica)." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5469/1/chiarini_francesca_tesi.pdf.

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The most ocean - atmosphere exchanges take place in polar environments due to the low temperatures which favor the absorption processes of atmospheric gases, in particular CO2. For this reason, the alterations of biogeochemical cycles in these areas can have a strong impact on the global climate. With the aim of contributing to the definition of the mechanisms regulating the biogeochemical fluxes we have analyzed the particles collected in the Ross Sea in different years (ROSSMIZE, BIOSESO 1 and 2, ROAVERRS and ABIOCLEAR projects) in two sites (mooring A and B). So it has been developed a more efficient method to prepare sediment trap samples for the analyses. We have also processed satellite data of sea ice, chlorophyll a and diatoms concentration. At both sites, in each year considered, there was a high seasonal and inter-annual variability of biogeochemical fluxes closely correlated with sea ice cover and primary productivity. The comparison between the samples collected at mooring A and B in 2008 highlighted the main differences between these two sites. Particle fluxes at Mooring A, located in a polynia area, are higher than mooring B ones and they happen about a month before. In the mooring B area it has been possible to correlate the particles fluxes to the ice concentration anomalies and with the atmospheric changes in response to El Niño Southern Oscillations. In 1996 and 1999, years subjected to La Niña, the concentrations of sea ice in this area have been less than in 1998, year subjected to El Niño. Inverse correlation was found for 2005 and 2008. In the mooring A area significant differences in mass and biogenic fluxes during 2005 and 2008 has been recorded. This allowed to underline the high variability of lateral advection processes and to connect them to the physical forcing.
Gli ambienti polari rappresentano il luogo in cui avvengono i maggiori scambi tra atmosfera e oceano grazie alle basse temperature che favoriscono i processi di assorbimento dei gas atmosferici, in particolare di CO2. Le alterazioni dei cicli biogeochimici di queste regioni quindi possono avere un forte impatto sul clima globale. Ci si è proposti di contribuire alla definizione dei meccanismi che regolano attualmente i flussi biogeochimici nel Mare di Ross analizzando il particellato raccolto in vari anni (progetti ROSSMIZE, BIOSESO 1 e 2, ROAVERRS e ABIOCLEAR) in due siti fissi (mooring A e B). A tal fine è stato messo a punto un metodo di preparazione dei campioni di trappola più efficiente e sono stati elaborati i dati da satellite relativi alla concentrazione dei ghiacci, di clorofilla a e di diatomee. In ognuno degli anni esaminati, in entrambi i siti, si è osservata un’alta variabilità stagionale e interannuale dei flussi biogeochimici strettamente correlata alla copertura di ghiaccio e alla produttività primaria. Il confronto tra i campioni del 2008 raccolti dai mooring A e B ha evidenziato le principali differenze tra i due siti: nel mooring A, situato nell’area di polynia, flussi più alti e anticipati di circa un mese rispetto al mooring B. Nella zona del mooring B i flussi di particelle sono stati correlati alle fluttuazioni dei ghiacci e alle variazioni atmosferiche dovute a El Niño Southern Oscillation. Nel 1996 e 1999, anni soggetti a La Niña, le concentrazioni dei ghiacci sono state minori mentre nel 1998, periodo soggetto a El Niño, maggiori. Correlazione inversa è stata riscontrata per il 2005 e il 2008. Nell’area del mooring A le consistenti differenze registrate nei flussi relativi al 2005 e 2008, hanno consentito di evidenziare l’alta variabilità dei fenomeni di avvezione laterale e di collegarli al forcing fisico.

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Chiarini, Francesca <1983&gt. "Study of the inter-annual variability of particle vertical fluxes in two moorings in the Ross Sea (Antarctica)." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5469/.

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The most ocean - atmosphere exchanges take place in polar environments due to the low temperatures which favor the absorption processes of atmospheric gases, in particular CO2. For this reason, the alterations of biogeochemical cycles in these areas can have a strong impact on the global climate. With the aim of contributing to the definition of the mechanisms regulating the biogeochemical fluxes we have analyzed the particles collected in the Ross Sea in different years (ROSSMIZE, BIOSESO 1 and 2, ROAVERRS and ABIOCLEAR projects) in two sites (mooring A and B). So it has been developed a more efficient method to prepare sediment trap samples for the analyses. We have also processed satellite data of sea ice, chlorophyll a and diatoms concentration. At both sites, in each year considered, there was a high seasonal and inter-annual variability of biogeochemical fluxes closely correlated with sea ice cover and primary productivity. The comparison between the samples collected at mooring A and B in 2008 highlighted the main differences between these two sites. Particle fluxes at Mooring A, located in a polynia area, are higher than mooring B ones and they happen about a month before. In the mooring B area it has been possible to correlate the particles fluxes to the ice concentration anomalies and with the atmospheric changes in response to El Niño Southern Oscillations. In 1996 and 1999, years subjected to La Niña, the concentrations of sea ice in this area have been less than in 1998, year subjected to El Niño. Inverse correlation was found for 2005 and 2008. In the mooring A area significant differences in mass and biogenic fluxes during 2005 and 2008 has been recorded. This allowed to underline the high variability of lateral advection processes and to connect them to the physical forcing.
Gli ambienti polari rappresentano il luogo in cui avvengono i maggiori scambi tra atmosfera e oceano grazie alle basse temperature che favoriscono i processi di assorbimento dei gas atmosferici, in particolare di CO2. Le alterazioni dei cicli biogeochimici di queste regioni quindi possono avere un forte impatto sul clima globale. Ci si è proposti di contribuire alla definizione dei meccanismi che regolano attualmente i flussi biogeochimici nel Mare di Ross analizzando il particellato raccolto in vari anni (progetti ROSSMIZE, BIOSESO 1 e 2, ROAVERRS e ABIOCLEAR) in due siti fissi (mooring A e B). A tal fine è stato messo a punto un metodo di preparazione dei campioni di trappola più efficiente e sono stati elaborati i dati da satellite relativi alla concentrazione dei ghiacci, di clorofilla a e di diatomee. In ognuno degli anni esaminati, in entrambi i siti, si è osservata un’alta variabilità stagionale e interannuale dei flussi biogeochimici strettamente correlata alla copertura di ghiaccio e alla produttività primaria. Il confronto tra i campioni del 2008 raccolti dai mooring A e B ha evidenziato le principali differenze tra i due siti: nel mooring A, situato nell’area di polynia, flussi più alti e anticipati di circa un mese rispetto al mooring B. Nella zona del mooring B i flussi di particelle sono stati correlati alle fluttuazioni dei ghiacci e alle variazioni atmosferiche dovute a El Niño Southern Oscillation. Nel 1996 e 1999, anni soggetti a La Niña, le concentrazioni dei ghiacci sono state minori mentre nel 1998, periodo soggetto a El Niño, maggiori. Correlazione inversa è stata riscontrata per il 2005 e il 2008. Nell’area del mooring A le consistenti differenze registrate nei flussi relativi al 2005 e 2008, hanno consentito di evidenziare l’alta variabilità dei fenomeni di avvezione laterale e di collegarli al forcing fisico.

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Alimohammadi, Negin. "Modeling Annual Water Balance in The Seasonal Budyko Framework." Master's thesis, University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5099.

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In this thesis, the role of soil water storage change on the annual water balance is evaluated based on observations at a large number of watersheds located in a spectrum of climate regions, and an annual water balance model is developed at the seasonal scale based on Budyko hypthesis. The annual water storage change is quantified based on water balance closure given the available data of precipitation, runoff, and evaporation estimated from remote sensing data and meteorology reanalysis. The responses of annual runoff, evaporation, and storage change to the interannual variability of precipitation and potential evaporation are then analyzed. Both runoff and evaporation sensitivities to potential evaporation are higher under energy-limited conditions, but storage change seems to be more sensitive to potential evaporation under the conditions in which water and energy are balanced. Runoff sensitivity to precipitation is higher under energy-limited conditions; but both evaporation and storage change sensitivities to precipitation are higher under water-limited conditions. Therefore, under energy-limited conditions, most of precipitation variability is transferred to runoff variability; but under water-limited conditions, most of precipitation variability is transferred to storage change and some of precipitation variability is transferred to evaporation variability. The main finding of this part is that evaporation variability will be overestimated by assuming negligible storage change in annual water balance, particularly under water-limited conditions. Budyko framework which expresses partitioning of water supply at the mean annual scale, is adapted to be applicable in modeling water cycle in short terms i.e., seasonal and interannual scales. Seasonal aridity index is defined as the ratio of seasonal potential evaporation and the difference between precipitation and storage change. The seasonal water balance is modeled by using a Budyko-type curve with horizontal shifts which leads prediction of seasonal and annual storage changes and evaporation if precipitation, potential evaporation, and runoff data are available.
M.S.
Masters
Civil, Environmental, and Construction Engineering
Engineering and Computer Science
Civil Engineering; Water Resources Engineering

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22

Regonda, Satish Kumar. "Intra-annual to inter-decadal variability in the upper Colorado hydroclimatology: Diagnosis, forecasting and implications for water resources management." Diss., Connect to online resource, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3239392.

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23

Greene, Nicola. "Intra-annual variability in standards of water and sanitation in Upper Humla, Nepal : an investigation into the causes, importance and impact." Thesis, Loughborough University, 2014. https://dspace.lboro.ac.uk/2134/16183.

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This study investigates the impact of seasonality on standards of water and sanitation in the mountainous district of Humla, Nepal. The research considers impact on two levels: community level access and service delivery. First of all, it examines annual variation in village level access to water and sanitation. Secondly, it looks at the wider picture of service delivery and considers how seasonal variations present opportunities and challenges for improvement in standards for water and sanitation. Three case studies from Humla are presented which illustrate village level access to water and sanitation over a calendar year. These case studies summarise the content of 45 semi-structured interviews, 9 focus group discussions and 9 months of observational work in the district. Variations in weather, village population, infrastructure functionality, and environmental conditions are found to influence the experienced levels of access to water and sanitation at any given time. The impact of seasonality on service delivery was investigated via 39 key informant interviews. Both climatic (e.g. weather) and non-climatic (e.g. budget timings) sources of seasonality are found to impact programme implementation. The mismatch of local seasonal calendars and those imposed by central hubs is found to cause particular difficultly in effective delivery of water and sanitation services. The findings of this research have theoretical, methodological and practical implications. Theoretically, it is suggested that a mountain community s level of access to water and sanitation varies considerably over the course of a calendar year to the point where it needs to be considered if on the ground standards are to be improved. Methodological guidance is provided detailing means of investigating seasonality and its impact on standards of water and sanitation in other scenarios. Practical suggestions focus on incorporating seasonality into assessments of access to water and sanitation and programme delivery in mountain communities.

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24

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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Hauck, Judith [Verfasser], Dieter [Akademischer Betreuer] Wolf-Gladrow, and Birgit [Akademischer Betreuer] Schneider. "Processes in the Southern Ocean carbon cycle: Dissolution of carbonate sediments and inter-annual variability of carbon fluxes / Judith Hauck. Gutachter: Dieter Wolf-Gladrow ; Birgit Schneider. Betreuer: Dieter Wolf-Gladrow." Bremen : Staats- und Universitätsbibliothek Bremen, 2012. http://d-nb.info/1071993844/34.

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26

Saunders, Ryan Alexander. "Ecological investigations of euphausiids at high latitudes." Thesis, St Andrews, 2007. http://hdl.handle.net/10023/347.

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27

Torp, Mikaela. "The effect of snow on plants and their interactions with herbivores." Doctoral thesis, Umeå : Department of Ecology and Environmental Science, Umeå University, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-30444.

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Reboita, Michelle Simões. "Elementos da variabilidade climática no extremo sul do Brasil, no Período de 1990 a 2001." reponame:Repositório Institucional da FURG, 2004. http://repositorio.furg.br/handle/1/3488.

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Dissertação(mestrado) - Universidade Federal do Rio Grande, Programa de Pós-Graduação em Engenharia Oceânica, Escola de Engenharia, 2004.
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A variabilidade climática,por exercer grande influência nas civilizações ao longo do tempo, tem atraído a atenção dos pesquisadores contemporâneos que buscam o desenvolvimento de modelos climáticos que consigam reproduzi-la. O objetivo deste estudo é a determinação dos sistemas atmosféricos que causam maior variabilidade climática no extremo sul do Brasil, a fim de prover informações para a elaboração futura de um modelo climático regional. Paratanto, empregou-se a transformada de ondeleta a dois conjuntos de dados, um medido na estação meteorológica convencional situada a 32º04’S e 52º10’W, no período de 1º de janeiro de 1990 a 19 de março de 2001, e outro medido em uma bóia de fundeio localizada aproximadamente a 32º54’S e 50º48’W no oceano Atlântico sudoeste, no período de 1º de junho de 2001 a 8 de maiode 2002. Observou-se que a maior variância de ondeleta em todas as variáveis atmosféricas esteve associada ao ciclo anual, com exceção das componentes zonal e meridional da velocidade do vento e da precipitação. Nestas três variáveis a maior energia foi relacionada à passagem de massas de ar e a formação de sistemas frontais e estes sistemas, por sua vez,assumiram maior importância quando o ciclo anual foi descontado das demais variáveis. Portanto, pode-se inferir que o ciclo anual é o responsável pela maior parte da variabilidade climática no extremo sul do Brasil juntamente com as massas de ar e sistemas frontais. Entretanto, o clima desta região também é afetado pelas oscilações de Madden-Julian, bloqueios atmosféricos e fenômeno El Niño-Oscilação Sul. A associação dos períodos observados na transformada de ondeleta com os eventos atmosféricos foi possível devido a grande eficiência desta metodologia em decompor os sinais em ambos os domínios de tempo e escala.
Climate variability has called the attention of contemporary researchers due to the fact that it exerts large influence on the civilizations throughout time. The development of climatic models aims at reproducing it. The purpose of this study is to establish the atmospheric systems which cause the largest climate variability in the extreme south of Brazil,in order to provide information for the future elaboration of a regional climate model. The wavelet transform was applied to two sets of data: one measured in the conventional meteorological station located at 32º04’S and 52º10’W, from January 1st, 1990 to March 19th, 2001, and the other one measured on a buoy approximately at 32º54’S and 50º48’W in the southwestern Atlantic, from June 1st, 2001 to May 8th, 2002. The largest wavelet variance in all atmospheric variables was associated with the annual cycle, except the zonal and meridional components of the wind velocity and precipitation. In these three ones, the largest variance was related to the passage of air masses and the frontal systems formation. When the annual cycle was subtracted from the series, the largest energy was associated with the passage of air masses and the frontal systems formation. Therefore, it could be inferred that the annual cycle is responsible for most of the climate variability in the region along with the air masses and the frontal systems. However, the climate in this region is also affected by Madden-Julian oscillation, atmospheric blocking, and the El Niño – Southern Oscillation. The wavelet transform is a powerful metodology for signal decomposition, because itallows determining the periodicity and the temporal location of the phenomena. Thus, an association with atmospheric events can be accomplished.

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Marzin, Anahita. "Indicateurs biologiques de la qualité écologique des cours d’eau : variabilités et incertitudes associées." Thesis, Paris, AgroParisTech, 2013. http://www.theses.fr/2013AGPT0002/document.

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Evaluer, maintenir et restaurer les conditions écologiques des rivières nécessitent des mesures du fonctionnement de leurs écosystèmes. De par leur complexité, notre compréhension de ces systèmes est imparfaite. La prise en compte des incertitudes et variabilités liées à leur évaluation est donc indispensable à la prise de décision des gestionnaires. En analysant des données nationales (~ 1654 sites), les objectifs principaux de cette thèse étaient de (1) tester certaines hypothèses intrinsèques aux bio-indicateurs et (2) d'étudier les incertitudes de l'évaluation écologique associées à la variabilité temporelle des bio-indicateurs et à la prédiction des conditions de référence. (1) Ce travail met en évidence (i) le rôle prépondérant des facteurs environnementaux naturels dans la structuration des communautés aquatiques en comparaison des facteurs anthropiques (définis à l'échelle du bassin versant, du corridor riparien et du tronçon), (ii) les réponses contrastées des communautés aquatiques aux pressions humaines (dégradations hydro-morphologiques et de la qualité de l'eau) et (iii) plus généralement, les forts impacts des barrages et de l'altération de la qualité de l'eau sur les communautés aquatiques. (2) Une méthode Bayésienne a été développée pour estimer les incertitudes liées à la prédiction des conditions de référence d'un indice piscicole (IPR+). Les incertitudes prédictives de l'IPR+ dépendent du site considéré mais aucune tendance claire n'a été observée. Par comparaison, la variabilité temporelle de l'IPR+ est plus faible et semble augmenter avec l'intensité des perturbations anthropiques. Les résultats de ce travail confirment l'avantage d'indices multi-métriques basés sur des traits fonctionnels par rapport à ceux relatifs à la composition taxonomique. Les sensibilités différentes des macrophytes, poissons, diatomées et macro-invertébrés aux pressions humaines soulignent leur complémentarité pour l'évaluation des écosystèmes fluviaux. Néanmoins, de futures recherches sont nécessaires à une meilleure compréhension des effets d'interactions entre types de pressions et entre pressions humaines et environnement
Sensitive biological measures of ecosystem quality are needed to assess, maintain or restore the ecological conditions of rivers. Since our understanding of these complex systems is imperfect, river management requires recognizing variability and uncertainty of bio-assessment for decision-making. Based on the analysis of national data sets (~ 1654 sites), the main goals of this work were (1) to test some of the assumptions that shape bio-indicators and (2) address the temporal variability and the uncertainty associated to prediction of reference conditions.(1) This thesis highlights (i) the predominant role of physiographic factors in shaping biological communities in comparison to human pressures (defined at catchment, riparian corridor and reach scales), (ii) the differences in the responses of biological indicators to the different types of human pressures (water quality, hydrological, morphological degradations) and (iii) more generally, the greatest biological impacts of water quality alterations and impoundments. (2) A Bayesian method was developed to estimate the uncertainty associated with reference condition predictions of a fish-based bio-indicator (IPR+). IPR+ predictive uncertainty was site-dependent but showed no clear trend related to the environmental gradient. By comparison, IPR+ temporal variability was lower and sensitive to an increase of human pressure intensity. This work confirmed the advantages of multi-metric indexes based on functional metrics in comparison to compositional metrics. The different sensitivities of macrophytes, fish, diatoms and macroinvertebrates to human pressures emphasize their complementarity in assessing river ecosystems. Nevertheless, future research is needed to better understand the effects of interactions between pressures and between pressures and the environment

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30

Barroso, Cássia Pianca. "Variabilidade espaço-temporal da morfologia costeira: resultados de sensoriamento remoto." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/21/21136/tde-16032015-155053/.

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A habilidade de prever mudanças morfológicas nas regiões costeiras é restringida pela falta de dados observacionais com suficiente resolução espacial e temporal. Com o desenvolvimento do sensoriamento remoto, esse problema pode ser minimizado, especialmente com o uso de câmeras de vídeo para o estudo de regiões costeiras. Os objetivos dessa tese são, através do uso de imagens de vídeo, (1) desenvolver um método robusto para extrair a localização da linha de costa; (2) analisar um conjunto de dados inéditos de 26 anos de imagens diárias; (3) caracterizar as escalas espaciais e temporais da variação da linha de costa em um local representativo, a praia de Duck, NC; (4) testar esse método em uma praia reflectiva e com cúspides, a praia de Massaguaçu localizada no litoral brasileiro; (5) descrever recentes observações de feições morfológicas de meso-escalas associadas a um canal de marés usando uma técnica óptica inovadora e documentar as taxas e padrões de migração dessas feições morfológicas em New River Inlet, NC. Um modelo foi desenvolvido, chamado ASLIM (Augmented ShoreLine Intensity Maxima) para extrair as posições da linha de costa baseado na intensidade máxima observada nas imagens de exposição (timex) através de um ajuste Gaussiano com um subsequente filtro Kalman filtro, este para reduzir incertezas e ruídos. O ASLIM quando comparado com dados do levantamentos batimétricos mostrou um boa correlação com coeficiente de 0.85, estatisticamente significativo). As ondas foram caracterizadas em termos da altura significativa e os componentes longitudinal e transversal do fluxo de energia da onda (Px e Py, respectivamente). Menos de 2\\% da altura da onda é explicada por escalas maiores do que um ano. 66\\% da variância foi explicada por períodos maiores do que o ciclo anual, apesar do fato das forçantes (ondas) serem dominadas por períodos curtos (menores que 20 dias). O primeiro modo da EOF para a variação da linha de costa contém 49\\% da variância e representou o movimento transversal da linha de costa. O segundo modo (26\\% da variância) está associado com a alternância de sinais de acresção em cada lado píer, enquanto que os modos mais altos (7\\% e 5.6\\%) descrevem os efeitos locais do píer. O píer apresentou uma influência significativa no comportamento da linha de costa, à qual estende-se a 500 metros ao norte e sul do píer, duas vezes mais do que os valores assumidos por estudos anteriores. O píer restringe o transporte longitudinal sazonal entre a parte sul (verão) e a parte norte (inverno), resultando em uma acumulação de sedimentos sazonalmente reversa no lado up-drift da deriva. Sinais de erosão foram encontrados ao lado down-drift do píer e que propagam-se 1200 m/ano para longe do píer. A linha de costa apresentou uma tendência à erosão apenas no lado norte do píer, esta erosão pode estar relacionada com a tendência de aumento do transporte longitudinal para o norte, que é bloqueado devido ao píer, gerando uma acumulação na parte sul do píer e erosão na parte norte. O método ASLIM também foi testado na Praia de Massaguaçu e mostrou ser uma valiosa ferramenta para investigar variabilidade da linha de costa. Nossas observações em New River Inlet (NC), revelaram um complexo de bancos de espraiamento e feições arenosas de meso-escalas que migraram em um padrão coerente horário onde nas regiões offshore migraram em direção contrária a desembocadura do rio enquanto que as feições na região próxima a costa, migraram em direção ao canal. Para quantificar de forma objetiva as taxas e padrões de migração um algoritmo foi desenvolvido (LLSA - Lagged Least Square Algorithm) usando sequências de imagens de exposição (timex). Esse método compara diferentes imagens que possuem diferentes intervalos de tempo, e encontra o intervalo (lag) onde essas imagens são similares. A taxa média de migração encontrada foi de 1.53 m/dia (com desvio padrão de 0.76 m/dia). 72\\% das taxas estimadas foram maiores que 1.0 m/dia, 31\\% foram maiores que 2 m/dia, e as taxas máximas encontradas foram 3.5 m/day, em 23 dias. As taxas de migração média longitudinais mostraram um nó em 110 metros da linha de costa que separa as feições que migram para longe do canal (offshore) e para a linha de costa. O padrão circular pareceu ser consistente com o fluxo residual esperado em um delta de maré vazante. Em conclusão, nossos resultados mostraram que o uso de câmeras de vídeo são uma ótima ferramenta para fornecer informações sobre a dinâmica de morfologias costeiras com alta resolução temporal e espacial, de curto à longo-prazo.
The ability to predict changes of the coastal morphology has been restricted by the lack of observational data in a sufficient spatial and temporal coverage. With the advent of remote sensing, the low spatial and temporal resolution could be overcome, especially with the development of video cameras to study nearshore environments. The goals of this thesis are, using remote sensing techniques, to (1) develop a robust method for extracting shoreline locations; (2) analyze a unique 16 and 26-year record of daily to hourly video images; (3) characterize the space-time scales of shoreline variability at a representative site at Duck, NC; (4) test this method at a reflective and cuspy beach at Massaguaçu Beach located at Brazilian coast; (5) describe recent observations of meso-scales morphology associated with tidal inlets using an innovative optical method and document rates and patterns of migration of these features at New River Inlet, NC. A model was developed, called ASLIM (Augmented ShoreLine Intensity Maxima) to extract the shoreline positions based on fitting the band of high light intensity in time exposure images to a local Gaussian fit with a subsequent Kalman filter to reduce noise and uncertainty. The ASLIM model showed good agreement with survey data (correlation coefficient of 0.85, significant at 95\\% confidence level). Wave forcing was characterized in terms of the significant wave height and the cross-shore and longshore components of wave energy flux. 66\\% of the shoreline variability was explained by periods longer than the annual cycle, despite the fact that wave forcing is dominated by shorter periods. The first EOF mode of shoreline variability contained 49\\% of the variance and represented the cross-shore movement (landward- seaward) of the shoreline. The second mode (26\\% of the variance) is associated with alternating accretion signals on either side of the pier, while the next two higher EOFs (7\\% and 5.6\\%) describe the local pier effects. The pier was found to have a significant influence on shoreline behavior that extends out to 500 meters, nearly twice the length scales assumed by previous studies. The pier restricts seasonal longshore transport from the south (summer) and north (winter) sides, resulting in a seasonally-reversing sediment accumulation on the up-drift side. Erosion signals on the down-drift side of the pier were found propagate away from the pier at 1200 m/year. A shoreline erosion trend that was found only on the north side of the pier may be related to the trend found in the alongshore transport, that it is increasing toward the north and is being blocked by the pier. The ASLIM method was also tested at Massaguaçu Beach and showed to be a valuable tool to investigate shoreline variability processes. Our observations, at New Rivet Inlet (NC), revealed a complex set of swash bars and meso-scale sand banks that migrated in a coherent clockwise pattern with movement in offshore regions being away from the inlet mouth while nearshore migration was back toward the inlet. To quantify migration rates and patterns objectively based on sequences of time exposure images, a Lagged Least Squares Algorithm (LLSA) was developed that found the vector migration rate for which the suite of lagged images were most similar, computed on a tile-by-tile basis. The mean migration rate was found to be 1.53 m/day (standard deviation of 0.76 m/day). 72\\% percent of estimated rates were greater than 1.0 m/day, 31\\% percent were larger than 2.0 m/day, and the maximum rate round was 3.5 m/day, averaged over 23 days. Alongshore averages of cross-shore migration rates showed a node at 110 m from the shoreline that separates migration away from the inlet (offshore) from migration toward the inlet near the shore. The circular pattern of migration appeared to be consistent with expected residual flow on an ebb delta. In conclusion, our results showed that the use of video cameras are a useful tool for providing information about the dynamics of coastal morphologies with a high temporal and spatial resolution, from short to long-term.

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31

Koks, Josephus [Verfasser], Edzo [Akademischer Betreuer] Veldkamp, Alexander [Gutachter] Knohl, and Heinz [Gutachter] Flessa. "Tropical forest conversion to rubber and oil palm plantations: landscape-scale and inter-annual variability of soil greenhouse gas (GHG) fluxes and the contribution of tree-stem emissions to the soil GHG budget in Jambi province, Sumatra, Indonesia / Josephus Koks ; Gutachter: Alexander Knohl, Heinz Flessa ; Betreuer: Edzo Veldkamp." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2020. http://d-nb.info/1213096316/34.

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32

Barral, Quentin-Boris. "Caractérisation du front Nord-Baléares : Variabilité et rôle de la circulation des masses d'eau en Méditerranée Occidentale." Electronic Thesis or Diss., Toulon, 2022. http://www.theses.fr/2022TOUL0006.

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La Méditerranée Occidentale est l’un des bassins avec le plus de pollution plastique au monde, et son réchauffement de surface est quatre fois plus intense que celui des océans. Elle est dite "bassin laboratoire" pour l’étude de l’océan global : elle développe sa propre circulation de retournement. Sa courantologie est composée de 4 couches et d’environ 6 masses d’eau. La rencontre de deux masses d’eau de différentes températures et salinités en surface crée un front thermohalin. Cette thèse présente des avancées récentes sur la caractérisation des zones de fronts et sur la dynamique des masses d’eau en Méditerranée Occidentale. La détection de fronts de surface dans une simulation, et sur des observations satellites, a produit des cartes de statistiques de présence des fronts. Deux zones majeures de fronts, de température et de salinité, apparaissent dans le centre du bassin et se révèlent très différentes.La première est thermique, estivale et sur une profondeur de 50m. Elle part des Pyrénées mais s’estompe vers le nord-ouest de la Corse. La deuxième est haline, quasi-permanente et sur 200m de profondeur. Elle relie nettement les îles Baléares au sud-ouest de la Sardaigne. Précédemment confondues au sein d’un seul « front Nord-Baléares », leurs différentes origines et localisations impliquent que deux nouvelles appellations soient proposées. La zone de fronts halins marque la frontière entre eaux atlantiques jeunes du sud (AW) et vieilles du nord (mAW). Elle se fait déplacer vers le sud lors de la formation d’eau profonde (DWF) interannuelle du bassin provençal, et remonte ensuite vers le nord sous l’influence des tourbillons algériens (AEs). Le développement d’un algorithme de séparation des 6 différentes masses d’eau a permis de décrire la circulation particulière de chacune d’entre elles dans la simulation. Les circulations moyennes coïncident avec la littérature connue. Puis, outre un évènement irréaliste de circulation profonde, deux résultats importants sont déduits. D’une part, la simulation montre que la DWF du bassin provençal semble disloquer le gyre profond Est-Algérien, modifiant à son tour la trajectoire des AEs en surface. D’autre part, la DWF de 2005 a induit en 2009 un transit d’eau profonde vers la mer Tyrrhénienne.Néanmoins, ce transit a provoqué en surface un courant de retour de mAWs par le canal de Sardaigne vers le bassin algérien, au lieu d’un apport habituel par le canal Corse, et entraînant exceptionnellement de l’AW jusqu’en mer Ligure
The Western Mediterranean is one of the basins with the most plastic pollution in the world, and its surface warming is four times more intense than that of the oceans. It is a so-called "laboratory basin" for the study of the global ocean : it develops its own overturning circulation. Its currentology is composed of 4 layers and about 6 water masses. The meeting of two water masses of different surface temperatures and salinities creates a thermohaline front. This thesis presents recent advances in the characterisation of front zones and water mass dynamics in the Western Mediterranean. The detection of surface fronts in a simulation, and on satellite observations, has produced maps of front presence statistics. Two major zones of fronts, of temperature and salinity, appear in the centre of the basin and are very different. The first is thermal, summer and 50m deep. It starts in the Pyrenees but fades towards the north-west of Corsica. The second is haline, quasi-permanent and over 200m depth. It clearly connects the Balearic Islands to southwestern Sardinia. Previously confused within a single "North Balearic front", their different origins and locations imply that two new designations are proposed. The haline front zone marks the boundary between young southern Atlantic waters (AW) and old northern waters (mAW). It is displaced southwards during the interannual deep water formation (DWF) of the Provençal basin, and then moves northwards under the influence of Algerian eddies (AEs). The development of an algorithmfor separating the 6 different water masses allowed the description of the particular circulation of each of them in the simulation. The average circulations coincide with the known literature. Then, besides an unrealistic deep circulation event, two important results are deduced. On the one hand, the simulation shows that the DWF of the Provençal Basin seems to dislocate the deep East Algerian gyre, modifying in turn the trajectory of the surface AEs. On the other hand, the 2005 DWF induced a deep water transit towards the Tyrrhenian Sea in 2009. However, this transit induced a surface return flow of mAWs through the Sardinia Channel towards the Algerian Basin, instead of the usual inflow through the Corsica Channel, and exceptionally causing AWto reach the Ligurian Sea

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Mayot, Nicolas. "La saisonnalité du phytoplancton en Mer Méditerranée." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066440/document.

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Le phytoplancton est un élément primordial dans les réseaux trophiques marins et il est un acteur principal dans les cycles biogéochimiques de la planète. Cependant, des incertitudes subsistent autour des facteurs environnementaux influençant sa saisonnalité ainsi que sa capacité à se développer. L’objectif majeur de cette thèse est d’étudier la réponse du phytoplancton à la variabilité interannuelle des facteurs environnementaux en Mer Méditerranée. Plus précisément, il s’agit de déterminer l’influence de ces derniers sur la saisonnalité du phytoplancton.Dans un premier temps, la variabilité interannuelle des cycles annuels de biomasses phytoplanctoniques observables en Méditerranée a été analysée. Certaines régions, tel que les zones de formation d’eau dense, présentent une variabilité interannuelle importante. L’une des régions les plus variables est la zone de formation d’eau dense en Méditerranée Nord-Occidentale. Une approche multi-outils basée sur des observations a été mise en place pour l’étude des variations spatiale et temporelle de la saisonnalité du phytoplancton dans cette région. Le rôle crucial du mélange vertical et de la disponibilité en lumière sur la saisonnalité du phytoplancton a été évalué. Il est démontré qu’une couche de mélange profonde pendant l’hiver augmente l’intensité du bloom phytoplanctonique printanier, due à une présence plus importante dans la communauté phytoplanctonique de micro-phytoplancton. En conséquence, le taux de production primaire printanier augmente. Enfin, ces modifications de la communauté phytoplanctonique et de la production provoquent une augmentation du stock de carbone organique produit au printemps
The phytoplankton are essential for the oceanic trophic webs and for biogeochemical cycles on Earth. However, uncertainties remain about the environmental factors influencing its seasonality, and its growing efficiency. The main objective of this thesis is to characterize the responses of the phytoplankton to the interannual variability of the environmental factors, in the Mediterranean Sea. More precisely, we aim to assess the influence of the environmental factors on phytoplankton seasonality. The interannual variability of the phytoplankton annual cycles are analyzed in the Mediterranean Sea, thus highlighting the regions associated with annual cycle variability, like the ones where deep-water formation events occur recurrently. One of these regions is the North-Western Mediterranean Sea. A multiplatform approach based on in situ observations is implemented to analyze the spatial and temporal variability of the phytoplankton seasonality in this particular region. The influences of mixed layer depth and the light availability on phytoplankton seasonality are assessed. An intense deepening of the mixed layer (related to the deep convection) increases the magnitude of the phytoplankton spring bloom. Moreover, the strong deepening of mixed layer seems to induce favorable conditions for an important accumulation of micro-phytoplankton (composed of diatoms mainly). In turn, the phytoplankton production rate increases, mostly, the primary production rate of diatoms. Finally, at the scale of the North-Western Mediterranean Sea, the shift in the phytoplankton community structure and in production induces an increase of the organic carbon stock produced during spring

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Boulanger, Xavier. "Modélisation du canal de propagation Terre-Espace en bandes Ka et Q/V : synthèse de séries temporelles, variabilité statistique et estimation de risque." Thesis, Toulouse, ISAE, 2013. http://www.theses.fr/2013ESAE0009/document.

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Les bandes de fréquences utilisées conventionnellement pour les systèmes fixes de télécommunication par satellites (bandes C et Ku i.e. 4-15 GHz) sont congestionnées. Néanmoins, le marché des télécommunications civil et de défense accuse une demande de plus en plus importante en services multimédia haut-débit. Par conséquent, l'augmentation de la fréquence porteuse vers les bandes Ka et Q/V (20-40/50 GHz)est activement étudiée. Pour des fréquences supérieures à 5 GHz, la propagation des signaux radioélectriques souffre de l'atténuation troposphérique. Parmi les différents contributeurs à l'affaiblissement troposphérique total(atténuation, scintillation, dépolarisation, température de bruit du ciel), les précipitations jouent un rôle prépondérant. Pour compenser la détérioration des conditions de propagation, des techniques de compensation des affaiblissements (FMT: Fade Mitigation Technique) permettant d'adapter en temps réel les caractéristiques du système en fonction de l'état du canal de propagation doivent être employées. Une alternative à l'utilisation de séries temporelles expérimentales peu nombreuses est la génération de séries temporelles synthétiques d'atténuation due à la pluie et d'atténuation totale représentatives d'une liaison donnée.Le manuscrit est organisé autour de cinq articles. La première contribution est dédiée à la modélisation temporelle de l'affaiblissement troposphérique total. Le deuxième article porte sur des améliorations significatives du modèle de génération de séries temporelles d'atténuation due à la pluie recommandé par l'UITR.Les trois contributions suivantes constituent une analyse critique et une modélisation de la variabilité des statistiques du 1er ordre utilisées lors des tests des modèles de canal. La variance de l'estimateur statistique des distributions cumulatives complémentaires de l'atténuation due à la pluie et de l'intensité de précipitation est alors mise en évidence. Un modèle à application mondiale paramétré au moyen de données expérimentales est proposé. Celui-ci permet, d'une part, d'estimer les intervalles de confiance associés aux mesures de propagation et d'autre part, de quantifier le risque en termes de disponibilité annuelle associée à la prédiction d'une marge de propagation donnée. Cette approche est étendue aux variabilités des statistiques jointes. Elle permet alors une évaluation statistique de l'impact des techniques de diversité de site sur les performances systèmes, tant à microéchelle(quelques kms) qu'à macro-échelle (quelques centaines de kms)
Nowadays, C and Ku bands used for fixed SATCOM systems are totally congested. However, the demand of the end users for high data rate multimedia services is increasing. Consequently, the use of higher frequency bands (Ka: 20 GHz and Q/V 40/50 GHz) is under investigation. For frequencies higher than 5 GHz, radiowave propagation is strongly affected by tropospheric attenuation. Among the different contributors, rain is the most significant. To compensate the deterioration of the propagation channel, Fade Mitigation Techniques (FMT) are used. The lack of experimental data needed to optimize the real-time control loops of FMT leads tothe use of rain attenuation and total attenuation time series synthesizers. The manuscript is a compilation of five articles. The first contribution is dedicated to the temporal modelling of total impairments. The second article aims at providing significant improvements on the rain attenuation time series synthesizer recommended by ITU-R. The last three contributions are a critical analysis and a modelling of the variability observed on the 1st order statistics used to validate propagation channel models. The variance of the statistical estimator of the complementary cumulative distribution functions of rainfall rate and rain attenuation is highlighted. A worldwide model parameterized in compliance with propagation measurements is proposed. It allows the confidence intervals to be estimated and the risk on a required availability associated with a given propagation margin prediction to be quantified. This approach is extended to the variability of joint statistics. It allows the impact of site diversity techniques on system performances at small scale (few kms) and large scale (few hundred of kms) to be evaluated

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Omar, Youssouf Moussa. "Etude de l'habitat épipélagique du Golfe de Tadjourah (Djibouti) : structures de variabilité et processus qui les gouvernent." Thesis, Brest, 2016. http://www.theses.fr/2016BRES0017/document.

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L’objectif de cette thèse est d’étudier les caractéristiques physiques et biogéochimiques de l’habitat épipélagique (0-200 m), ses variabilités spatio-temporelles et les processus qui les gouvernent dans le Golfe de Tadjourah (Djibouti). L’analyse spectrale singulière (SSA) et la fonction empirique orthogonale (EOF) sont appliquées à deux jeux des données satellitales dérivées du radiomètre AVHRR_MetopA et des capteurs de la couleur de l’océan (Modis et Meris). Cette analyse statistique montre que les variabilités de la température de la surface de la mer (SST) et de la concentration de la chlorophylle a (CHLa) sont essentiellement expliquées par les cycles annuels et semi-annuels. Le cycle annuel de la SST montre l’alternance des eaux chaudes d’avril à octobre et des eaux froides de novembre à mars. Le cycle semi-annuel indique une légère baisse de la SST entre juillet et aout, particulièrement à l’ouest du golfe. Pour la CHLa, la variabilité est entièrement représentée par le cycle annuel. Celui-ci indique l’enrichissement des eaux du large avec un fort gradient côte-large de juillet à novembre et une tendance inverse de décembre à juin. En outre, l’analyse spectrale singulière multi-canal (M-SSA) et la fonction de corrélation croisée avec fenêtre de 120 jours, appliquées à l’ensemble des paramètres océanique (SST et CHLa) et atmosphériques (Vent, Température et humidité spécifique de l’air) révèlent que le cycle annuel de la SST est relié aux flux de chaleur à l’interface air-mer. En revanche, le refroidissement des eaux durant juillet-aout associé au pic de la CHLa, a été attribué au phénomène d’upwelling. Dans la seconde partie, afin d’élucider l’influence océanique sur la SST et la CHLa, les structures thermohalines and biogéochemiques de la couche supérieure (0-200 m) sont étudiées à l’aide des données collectées durant juillet-aout 2013, septembre 2013 et Février 2014. Les résultats montrent qu’en juillet-aout, la couche superficielle se composait d’une couche de mélange (CM) s’étendant sur environ 20-30 m de profondeur, suivie d’une thermocline localisée entre 30 and 50 m. La CM était réduite à l’ouest et au sud-est du golfe où le gradient thermique et la CHLa étaient plus élevées proche de la surface. En septembre, cette stratification persistait mais la CM était plus chaude et salée. En Février, la CM s’étendait sur environ 120 m de profondeur et la thermocline était moins prononcée. La comparaison des courants mesurés avec les courants de dérive d’ekman et les courants géostrophiques ont révélé que les structures thermohalines et biogéochimiques sont influencées par les vents de moussons du Sud-Ouest (MSO) et du Nord-Est (MNE). Les MSO qui soufflent de juin à aout, déplacent les eaux de surface du Golfe de Tadjourah vers le Golfe d’Aden et induisent la remontée des eaux profondes à l’ouest et l’intrusion par le nord-est des eaux salée de la thermocline. Celle-ci se rapproche de la surface particulièrement à l’ouest où elle se mélange avec les eaux de surface. En revanche, les vents de moussons du nord-est (MNE) prédominants de novembre à mai, emmènent les eaux froides vers le Golfe de Tadjourah. Le mélange convectif profond épaissit la CM. Cette thèse montre que les vents de moussons et leur renverse saisonnière jouent un rôle crucial dans la stratification de la colonne d’eau et que la topographie du bassin influence et module leurs effets. Durant l’été, la forme en cuvette du bassin et la pente continentale plus allongée à l’ouest favorise l’upwelling à l’ouest du golfe où les anomalies de la SST et de fortes concentrations de la CHLa ont été observées
The objective of this thesis is to study the physical and biogeochemical characteristics of the pelagic habitat (0-200m), its spatio-temporal variability and the processes that govern them in the Gulf of Tadjourah (Djibouti).Singular spectrum analysis (SSA) and empirical orthogonal function (EOF) were applied to two data sets derived from AVHRR_MetopA radiometry and sea colour sensors (Modis and Meris). These statistical analysis shows that the variability of sea surface temperature (SST) and chlorophyll a concentration (CHLa) are mainly explained by annual and semi-annual cycles. The annual cycle of SST consists of an alternation between warmer (April to October) and cooler (November to March) surface water. The semi-annual cycle shows a slight drop of SST between July and August, particularly in the west of the gulf. For the CHLa, the variability is fully dominated by the annual cycle indicating summer enrichment of seashore water (July-November) with a strong seaward gradient which is reversed from October to May. Multichannel spectrum analysis (M-SSA) and cross correlation function analysis applied to the oceanic (SST, CHL-a) and atmospheric parameters (wind speed, air temperature and humidity) showed that the annual cycle of SST is connected to heat flux at the air-sea interface, while the summer drop of SST and its associated CHL-a increase were attributed to upwelling. In the second part, in order to elucidate this oceanic influence on SST and CHL-a, the vertical thermohaline and biogeochemical structures of the upper layer (0-200 m) were studied using high-resolution hydrographic data collected in July-August 2013, September 2013 and February 2014. During summer, the superficial layer consisted of the mixed layer (ML) extending to a depth of about 20-30 m, followed by the thermocline located between 30 and 50 m depth. The ML was thicker in the west and the southeast where the thermal gradient and chlorophyll a concentrations were particularly high. During September, this stratification persisted but the ML became warmer and saltier and the thermocline moved slightly deeper. In February, the ML extended to about 120 m, and the thermocline was less pronounced. A comparison of the directly measured currents to the wind induced Ekman currents and to geostrophic current profiles revealed that the thermohaline and the biogeochemical features were related to the southeast and northeast monsoon winds (SWM & NEM). Between June and August, the SWM drives surface water from the Gulf of Tadjourah to the Gulf of Aden and thus induces the westward intrusion of high salinity thermocline water from the Gulf of Aden. This near surface flow mixes surface waters in the extreme west of the Gulf of Tadjourah. In contrast, the NEM which blow from September to May, bring cold water toward the Gulf of Tadjourah and thickens the ML through convective mixing. Our thesis shows that the monsoon winds and their seasonal reversal play a crucial role in the stratification of the water column, but that their effects are additionally influenced by basin topography. During summer the bowl-shape of the basin and its elongated slope in the west enhance the upwelling in this area where negative sea surface temperature anomalies and high chlorophyll a concentrations were observed

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Ahmad, Hafiz Bashir. "Intraspecific variability in embolism resistance and functional trade-offs in sunflower (Helianthus annuus L.) and Maritime pine (Pinus pinaster Ait.)." Thesis, Bordeaux, 2017. http://www.theses.fr/2017BORD0747/document.

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Plusieurs études ont montré que la productivité des forêts et des cultures décroît sur l’ensemble de la planète en réponse au changement climatique, et que les risques de mortalité liée à la sécheresse s’accroissent. Ces mortalités massives ont été observées dans tous les écosystèmes forestiers et seraient dues à un dysfonctionnement hydraulique des plantes, causé par de l’embolie xylémiène. Le spectre interspécifique de résistance à l'embolie a été largement étudiée, mais peu d'attention a été accordée à la variabilité intra-spécifique de ce trait. C’est pourquoi, l’objectif de ce travail de thèse était d’améliorer notre compréhension de la variabilité intra-spécifique de la résistance à l’embolie chez une espèce cultivée(Helianthus annuus L.) et chez un conifère (Pinus pinaster). Nous avons déterminé la vulnérabilité à l’embolie de quatre variétés de tournesol, présentant des différences significatives de P50 (pression induisant 50% de perte de conductivité hydraulique), allant de -2.67 à -3.22 MPa. Un compromis entre sécurité hydraulique et croissance a été observé mais pas entre la sécurité hydraulique et la capacité de transport de l'eau du xylème. Seuls quelques caractères anatomiques, tels que la densité des vaisseaux et la surface du lumen, présentent une corrélation avec la résistance à l’embolie. Dans un second temps, nous avons phénotypé pour la résistance à l’embolie et la densité du bois 477 génotypes de P. pinaster, issus d’une F2 de pleins-frères correspondant à la 3ème génération consanguine obtenue par auto-fécondation d’un hybride inter-provenance “Corse × Landes. La variabilité de la P50 au sein de l’espèce était extrêmement faible (CVP=5.6%). D’autre part, nous avons mis en évidence l’absence de compromis entre sécurité hydraulique et densité du bois. La part de variance du caractère P50 expliquée par QTLs (PEV)correspondait à 23.6% de la variance phénotypique totale mais aucun QTL commun n’a pu être détecté entre P50 et densité du bois, suggérant qu’au sein de cette famille, la plus forte résistance à l’embolie de certains génotypes n’est pas liée à un bois plus dense. Une analyse multi-caractère du fonctionnement de la feuille et du xylème a été réalisée via l’étude de la dynamique saisonnière de la fluorescence du photosystème II et des traits hydrauliques de la tige, sur une famille de pleins-frères d’un hybride interprovenance “Maroc × Landes” de P. pinaster ; en réponse à une diminution du potentiel hydrique,l’efficience du photosystème II et la conductance stomatique ont tous deux diminué, induisant une décroissance rapide du taux d’assimilation. La résistance à l’embolie du xylème n’a pas montré de relation significative avec les traits foliaires. L’absence de compromis entre ces caractères permet donc d’envisager la sélection génétique de génotypes à la fois efficients et résistants
As a consequence of current global climate change, forest and crop ecosystems are decreasing inproductivity worldwide and are under increased threat of widespread drought-induced mortality due tohydraulic failure caused by xylem embolism. The range of embolism resistance across species has been intensively studied but little attention has been paid to intraspecific variability. This thesis aimed thereforeat improving our understanding of the intraspecific variation in embolism resistance in one crop species(Helianthus annuus L.) and one conifer species (Pinus pinaster). In the first place, vulnerability to embolism was determined across four sunflower accessions with significant variations in P50 (pressure inducing 50% loss of hydraulic conductivity) ranging between -2.67 and -3.22 MPa. A trade-off between hydraulic safety and growth was observed but not between hydraulic safety and efficiency. Only few anatomical traits, such as vessel density and vessel lumen area, were found related to embolism resistance.Secondly, we phenotyped 477 P. pinaster full-sib F2 genotypes corresponding to a three-generation inbred pedigree obtained by the self-pollination of an inter “Corsica × Landes” provenance hybrid, for embolismresistance and wood density. The variability for P50 within species was remarkably low (CVP=5.6%). Wealso found a lack of trade-off between hydraulic safety and wood density. The phenotypic variance explained by QTLs (PEV) detected for P50 accounted for 23.6% of the phenotypic variation but no QTL collocated between P50 and wood density, suggesting that embolism resistant genotypes in this family are not dependent on denser wood. A multi-trait analysis of leaf and xylem functioning was performed through seasonal measurements of photosystem II fluorescence and stem hydraulic traits on a full-sib family of aninter “Morocco × Landes” provenance hybrid of P. pinaster; it revealed that with decreasing water potential, the efficiency of both photosystem II and stomatal conductance decreased which resulted in rapid decrease in assimilation rate. Xylem resistance to embolism was found having no relationship with leaf functioning traits. The absence of trade-off between these traits makes it possible to consider selection for both efficient and resistant genotypes

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Sandström, Helena. "Contouring variability in radiosurgery - dosimetric and radiobiological implications." Licentiate thesis, Stockholms universitet, Fysikum, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-123252.

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The use of Stereotactic Radiation Therapy (SRT) employing one large fraction of radiation, as in stereotactic radiosurgery (SRS), or few fractions of high doses, has continuously increased due to the technical development and the progress in dose delivery complemented by the positive clinical experience. The success of stereotactic radiation therapy depends on many clinical, dosimetric and radiobiological factors. For SRS in particular, the delivery of a highly conformal dose distribution to the target in one fraction allowing at the same time the sparing of the normal tissue and the critical structures is part of the basic concept of the technique. Provided that the highly accurate radiosurgical equipment available today is used, planning and delivering the prescribed dose distribution is an achievable goal, and therefore the main issue to be solved is the definition of the target. As the target volume in radiosurgery is usually defined without margins, the success of the stereotactic approach critically depends on the accurate delineation of the target which could be identified as a factor of key importance. In addition, the delineation of the Organs At Risk (OAR) is also critical. The purpose of this work was to evaluate the current degree of variability for target and OAR contouring and to establish methods for analysing multi-observer data regarding structure delineation variability. A multi-center target and OAR delineation study was initiated. Two complex and six common cases to be treated with SRS were selected and subsequently distributed to centers around the world performing Gamma Knife® radiosurgery for delineation and treatment planning. The resulting treatment plans and the corresponding delineated structures were collected and analysed. Results showed a very high variability in contouring for four complex radiosurgery targets. Similar results indicating high variability in delineating the OAR and reporting the doses delivered to them were also reported. For the common radiosurgery targets however, a higher agreement in the delineation was observed, although lower than expected. The assessment of the quality of treatment planning for radiosurgery is usually performed with respect to the coverage of the target, the planning specificity, and dose to the sensitive structures and organs close to the target. However, physical dose conformity to the target does not guarantee the success of the treatment. The assessment of the plan quality should also be performed with respect to the clinical outcome expressed as probability of controlling the target that should be irradiated. In this respect, this study also aimed to create the framework for assessing the impact of the inaccuracy in delineating the target on the predicted treatment outcome for radiosurgery targets known for their high potential to invade the neighbouring normal tissue, using radiobiological models. In addition, radiobiological models have also been used to determine the tumour control probability accounting for the oxygenation for stereotactic radiation therapy targets. The results suggest that radiobiological modelling has the potential to add to the current knowledge in SRS by theoretically assessing the key factors that might influence the treatment outcome.

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Huttunen, K. L. (Kaisa-Leena). "Biodiversity through time:coherence, stability and species turnover in boreal stream communities." Doctoral thesis, Oulun yliopisto, 2016. http://urn.fi/urn:isbn:9789526211602.

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Abstract Describing how and why species composition of ecological communities varies across spatial and temporal scales is a primary objective for ecological research. A key challenge is to distinguish changes in community composition resulting from external factors from the natural background variability. In this thesis I aimed to study: 1) the level of temporal variation in community composition of stream macroinvertebrates, 2) the role of different environmental factors to temporal variability, 3) the effect of temporal variability on bioassessment outcomes, and 4) comparability of different approaches to study community variability through time. A majority of the studied macroinvertebrate communities showed lower level of inter-annual variation, i.e. temporal turnover, than expected by chance. The observation of high community stability was further supported by the low level of inter-annual variation in taxonomic completeness (quotient of observed and expected number of species, O/E). Despite the low absolute variation in O/E, ecological status assessments varied annually. Thus the use of one year data may bias management decisions. Macroinvertebrate communities experienced similar dynamics across several spatial extents, from riffles within a stream to streams among regions, suggesting that large-scale extrinsic factors are the major driver of community dynamics. Especially climatically exceptional years may have a strong imprint on community variability. However, at the within-stream scale, coherence was lower than expected, indicating that community dynamics may be driven by different processes at different spatial extents. Stream macroinvertebrate community dynamics were strongly related to in-stream vegetation, temporal variability decreasing with increasing macrophyte cover. Importantly, the effect of in-stream vegetation on temporal turnover of macroinvertebrate communities was masked by the stochastic effect of habitat connectivity, suggesting that unless stochastic effects are controlled for, the role of deterministic processes may be obscured, thus affecting our ability to understand and predict community changes through time. In addition, different approaches to study temporal variability may disagree on estimates for the level of temporal turnover and factors explaining it – a fact that should be taken into account when planning and comparing studies
Tiivistelmä Yksi ekologisen tutkimuksen keskeisistä tavoitteista on kuvata, miten ja miksi eliöyhteisöjen koostumus muuttuu paikasta ja ajankohdasta toiseen. On tärkeää pystyä erottamaan erilaisten ulkoisten tekijöiden aiheuttamat muutokset luonnollisesta taustavaihtelusta. Väitöskirjani tavoitteena oli selvittää 1) miten paljon virtavesien pohjaeläinyhteisöissä tapahtuu ajallista vaihtelua 2) mitkä ympäristötekijät vaikuttavat yhteisöjen ajalliseen vaihteluun 3) miten ajallinen vaihtelu vaikuttaa ympäristön tilan arviointiin ja 4) kuinka vertailukelpoisia ovat eri lähestymistavat ajallista vaihtelua tutkittaessa. Valtaosa tutkituista pohjaeläinyhteisöistä vaihteli vuosien välillä vähemmän kuin olisi sattumalta odotettavissa osoittaen varsin suurta ajallista pysyvyyttä. Käsitystä yhteisöjen pysyvyydestä tuki myös vähäinen vuosittainen vaihtelu ekologista tilaa kuvaavassa taksonomisessa eheydessä (=havaitun ja odotetun lajiston suhde O/E). Huolimatta näennäisen pienestä vaihtelusta O/E suhteessa paikkakohtaiset tilaluokka-arviot saattoivat vaihtua vuodesta toiseen. Yhden vuoden aineistoon perustuvat tilan arvioinnit voivat siis johtaa virheellisiin johtopäätöksiin. Pohjaeläinyhteisöjen ajallinen vaihtelu oli samankaltaista eri mittakaavoilla niin peräkkäisten koskipaikkojen kuin eri alueilla sijaitsevien purojen välillä. Suuren mittakaavan ympäristötekijät näyttävät siis säätelevän eliöyhteisöjen ajallista vaihtelua. Erityisesti ilmastotekijöiltään poikkeukselliset vuodet säätelevät eliöyhteisöjä, ja niiden vaikutus voi näkyä vielä useiden vuosien kuluttua. Vaihtelun samankaltaisuus peräkkäisten koskipaikkojen välillä oli kuitenkin odotettua pienempää. Yhteisöjä voivat siis säädellä osittain eri tekijät eri mittakaavoilla. Tutkittujen pohjaeläinyhteisöjen ajallisen vaihtelun voimakkuus liittyi erityisesti vesikasvillisuuden määrään: vaihtelu väheni kasvillisuuden lisääntyessä. Kasvillisuuden määrän vaikutus peittyi kuitenkin satunnaisten tekijöiden alle. Jos satunnaisia tekijöitä ei huomioida, deterministiset syy-seuraussuhteet voivat jäädä huomaamatta heikentäen mahdollisuuksiamme ymmärtää ja ennustaa eliöyhteisöjen vaihtelua. Lisäksi eri lähestymistavat ajallista vaihtelua tutkittaessa voivat johtaa erilaisiin arvioihin vaihtelun suuruudesta ja siihen vaikuttavista tekijöistä, mikä tulisi ottaa huomioon tutkimuksia suunnitellessa ja niiden tuloksia vertailtaessa

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Liguori, Antonio. "Stima della variabilità intra-annuale del regime dei deflussi idrici superficiali in bacini non strumentati." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amslaurea.unibo.it/8061/.

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La curva di durata di lungo periodo (POR) è uno strumento grafico molto efficace che mette in evidenza la relazione fra intensità e frequenza delle portate osservate in un determinato intervallo temporale. Essa è ricavata dall'idrogramma dei deflussi, ma presenta il problema della perdita di informazioni relative alla variabilità annuale e stagionali delle portate. Per tal motivo si è reso necessario l'utilizzo di due nuove interpretazioni delle curve di durate: le curve di durata annuali (alle quali può essere associato il concetto di percentile e quindi di probabilità di superamento di un particolare valore di portata) e le curve a base stagionale. La costruzione di tali curve, come nel caso delle POR complessive, è ostacolata dall'insufficienza di dati di portata, per cui sono utilizzate, a tale scopo, procedure di stima basate sulla regionalizzazione dei deflussi. Tra di esse è stato analizzata la tecnica geostatistica del Top-kriging applicata all'indice TND che sintetizza l'intera curva (Pugliese et al., 2014) nella ricostruzione, in cross-validazione, delle curve di durata annuali e stagionali di 182 bacini della regione sud-orientale degli Stati Uniti.

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Mayot, Nicolas. "La saisonnalité du phytoplancton en Mer Méditerranée." Electronic Thesis or Diss., Paris 6, 2016. http://www.theses.fr/2016PA066440.

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Le phytoplancton est un élément primordial dans les réseaux trophiques marins et il est un acteur principal dans les cycles biogéochimiques de la planète. Cependant, des incertitudes subsistent autour des facteurs environnementaux influençant sa saisonnalité ainsi que sa capacité à se développer. L’objectif majeur de cette thèse est d’étudier la réponse du phytoplancton à la variabilité interannuelle des facteurs environnementaux en Mer Méditerranée. Plus précisément, il s’agit de déterminer l’influence de ces derniers sur la saisonnalité du phytoplancton.Dans un premier temps, la variabilité interannuelle des cycles annuels de biomasses phytoplanctoniques observables en Méditerranée a été analysée. Certaines régions, tel que les zones de formation d’eau dense, présentent une variabilité interannuelle importante. L’une des régions les plus variables est la zone de formation d’eau dense en Méditerranée Nord-Occidentale. Une approche multi-outils basée sur des observations a été mise en place pour l’étude des variations spatiale et temporelle de la saisonnalité du phytoplancton dans cette région. Le rôle crucial du mélange vertical et de la disponibilité en lumière sur la saisonnalité du phytoplancton a été évalué. Il est démontré qu’une couche de mélange profonde pendant l’hiver augmente l’intensité du bloom phytoplanctonique printanier, due à une présence plus importante dans la communauté phytoplanctonique de micro-phytoplancton. En conséquence, le taux de production primaire printanier augmente. Enfin, ces modifications de la communauté phytoplanctonique et de la production provoquent une augmentation du stock de carbone organique produit au printemps
The phytoplankton are essential for the oceanic trophic webs and for biogeochemical cycles on Earth. However, uncertainties remain about the environmental factors influencing its seasonality, and its growing efficiency. The main objective of this thesis is to characterize the responses of the phytoplankton to the interannual variability of the environmental factors, in the Mediterranean Sea. More precisely, we aim to assess the influence of the environmental factors on phytoplankton seasonality. The interannual variability of the phytoplankton annual cycles are analyzed in the Mediterranean Sea, thus highlighting the regions associated with annual cycle variability, like the ones where deep-water formation events occur recurrently. One of these regions is the North-Western Mediterranean Sea. A multiplatform approach based on in situ observations is implemented to analyze the spatial and temporal variability of the phytoplankton seasonality in this particular region. The influences of mixed layer depth and the light availability on phytoplankton seasonality are assessed. An intense deepening of the mixed layer (related to the deep convection) increases the magnitude of the phytoplankton spring bloom. Moreover, the strong deepening of mixed layer seems to induce favorable conditions for an important accumulation of micro-phytoplankton (composed of diatoms mainly). In turn, the phytoplankton production rate increases, mostly, the primary production rate of diatoms. Finally, at the scale of the North-Western Mediterranean Sea, the shift in the phytoplankton community structure and in production induces an increase of the organic carbon stock produced during spring

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41

XuHan, Xu. "L'embryogénèse somatique chez le tournesol (Helianthus annuus L. ) : comparaison avec l'embryogénèse zygotique." Toulouse, INPT, 1999. http://www.theses.fr/1999INPT008A.

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L'embryogenese somatique chez le tournesol (helianthus annuus l. ), comparaison avec l'embryogenese zygotique. Dans le but d'accroitre la production d'embryons somatiques, un genotype recalcitrant a ete etudie par comparaison avec un genotype non-recalcitrant. Les embryogeneses primaire, secondaire et cyclique ainsi que leur utilisation pour le transfert de genes dans les tissus embryogenes ont ete developpees avec succes. Les mecanismes cellulaires et moleculaires impliques dans l'embryogenese somatique et les effets des tissus environnants ont ete etudies chez le genotype non-recalcitrant par comparaison avec l'embryogenese zygotique. Des similarites et des differences ont ete observees entre les 2 types d'embryons. Le suspenseur qui marque la premiere differenciation zygotique est souvent absent ou parfois remplace par une structure approchante chez l'embryon somatique. Le protoderme est present chez les deux types d'embryons mais absent chez les embryoides. La bipolarite de l'embryon zygotique est reliable a la polarite du sac embryonnaire et de l'albumen. L'origine des tissus et l'etat des tissus callogenes ont ete determinants en embryogenese somatique. Les lipides sont accumules de facon identique dans les 2 types d'embryons, par contre les grains d'amidon apparaissent plus precocement chez les embryons somatiques. Le dm bodipy paa, marqueur des canaux ioniques, marque le protoderme puis l'epiderme des 2 types d'embryons ainsi que l'extremite racinaire. Ceci s'accorde avec la fonction de ces tissus vis a vis de l'interaction avec l'environnement. Des differences dans l'expression des genes ont ete observees, en particulier pour le proteines lea qui apparaissent plus precocement chez les embryons somatiques et sont absentes des cals non-embryogenes, et confirmees par l'utilisation de 3 cdna.

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42

Azpiroz, Rivero Hilda Susana. "Analyse de la variabilité génétique d'Helianthus annuus à partir de la culture d'embryons." Paris 11, 1989. http://www.theses.fr/1989PA112136.

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Ce travail fait état de deux applications concrètes de la culture d'embryons immatures à l'amélioration du tournesol, l'objectif sous-jacent étant d'évaluer la variabilité génétique du matériel sur lequel ont été appliquées ces techniques. 1-L'une permet de créer des contraintes hydriques durant la culture "in vitro" au stade juvénile (embryon ou plantule), afin de sélectionner le matériel plus résistant au déficit hydrique. 2-L'autre se réfère à la culture "in vitro" des embryons immatures dans la fixation de lignées pures par la méthode de filiation monograine (SSD), afin d'accélérer la sélection. Pour la première approche, un hybride interspécifique entre H. Annuus et H. Anomalus a été fabriqué, dans le but d'obtenir du matériel possédant une base génétique élargie. Ceci pour faciliter la sélection "in vitro" des génotypes plus résistants au déficit hydrique. Nous avons constaté qu'au fur et à mesure que la concentration du mannitol augmente, le développement des embryons et des plantules diminue. Le potentiel hydrique foliaire aussi tend à diminuer avec l'augmentation de la concentration en mannitol. Les plantes adultes provenant de descendances sélectionnées par mannitol au stade "jeunes plantules", sont plus proches du phénotype H. Anomalus que celles qui proviennent des descendances témoins ou sélectionnées sur mannitol au stade "embryons". Le test sécheresse sur descendances F5 montre que le matériel qui a subi une sélection sur mannitol "in vitro", présente des réponses différentes par rapport au témoin vis-à-vis du stress. La méthode de sélection précoce sur "mannitol in vitro'' pourrait permettre, de façon relativement simple de sélectionner des plantes présentant certaines caractéristiques foliaires plus adaptées à supporter les conditions de sécheresse au champ. La deuxième approche nous a permis d'obtenir des semences F5 en 375 jours à partir du croisement diallèle initial de 7 parents. Les effets de la culture "in vitro" se traduisent par une série de modifications morphovégétatives et physiologiques sur les plantes qui ont été limitées par réduction de la durée du séjour "in vitro". L'évaluation de la variabilité génétique des lignées pures (F6) issues de la culture d'embryons immatures a été réalisée dans un délai de 890 jours. Les résultats montrent un élargissement de la variabilité au niveau des lignées issues du croisement diallèle par rapport aux parents. En outre le dispositif a permis de tester la présence d'épistasie (homozygote x homozygote) chez les lignées F6. L'analyse factorielle discriminante de l'aptitude à la combinaison, qui reflète une divergence génétique, a permis de détecter le rapport de parenté entre les géniteurs. D'autre part, entre les descendances F3 et F5, des corrélations phénotypiques significatives ont été mises en évidence pour 6 des caractères étudiés. Par contre une assez forte variation de ces deux types de corrélations a été constatée sur 3 familles entre les lignées F6 et la valeur hybride en F4
This work uses 2 concrete applications of the culture of young embryos for the Sunflower improvement, the principal aim being to evaluate the genetic variability of the material on which the technique was applied. 1-One application makes possible the induction of drought stress during "in vitro" culture to the young stage (embryos or plantlets) in order to select materials resistant to drought. 2-The other application is concerned with the "in vitro" culture of immature embryos in the production of imbred lines by single seeds descend method (SSd) in order to accelerate this selection. For the first approach an interspecific hybrid between H. Annuus and H. Anomalus was made in order to get some material possessing a larger genetic basis. This was to make possible the selection "in vitro" of genotypes that are more resistant to drought stress. We observed that, as the concentration of mannitol increased, the development of the embryos and the plantlets decreased, the leaf water potential also tended to decrease with the enhancement of mannitol concentration. The adult plants coming from progenies selected by mannitol at the young plantlet stage present nearer H. Anomalus phenotype, compared with controls or with mannitol selected embryons. The drought test on F5 progenies shows that the material which followed a mannitol "in vitro" culture reveals different reponses from the control or the drought stress. The early selection method involving "mannitol" application "in vitro" would make possible in a relatively simple way to select plants with specific foliage characteristics that would be advantageous adaptated to drought stress. With the second approach we obtained F5 seeds in 375 days from the initial diallel cross of 7 parents. The "in vitro" culture effects were expressed in a serie of morphovegetative and physiological modification in the plant which were limited by the reduction of the duration of the "in vitro" stage. The evaluation of the genetic variability of the imbreed lines (F6) issuing from the culture of young embryos was possible in a period of 890 days. The results show a growth in the variability of the lines got from the diallel crossing as compared to that of the parents. In addition the desing allowed estimations of the epistasis (homozygous * homozygous) in lines F6. The factor discriminant analysis of the combining abilities, which are the indicators of genetic divergence, gave us the relationships of the progeny. Furthermore, between the descendants F3 and F5 significative and positive phenotypic correlations were found evident for 6 of the characters studied. On the ether hand, a rather strong variation of the 2 types of correlations was recorded between 3 families of the lines F6 and their hybrids F4

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43

Persson, Anna. "Heart rate variability for driver sleepiness assessment." Thesis, Linköpings universitet, Institutionen för medicinsk teknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-157187.

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Studies have reported that around 20 % of all traffic accidents are caused by a sleepy driver. Sleepy driving has been compared to drunk driving. A sleepy driver is also an issue in the case of automated vehicles in the future. Handing back the control of the vehicle to a sleepy driver is a serious risk. This has increased the need for a sleepiness estimation system that can be used in the car to warn the driver when driving is not recommended. One commonly used method to estimate sleepiness is to study the heart rate variability, HRV, which is said to reflect the activity of the autonomous nervous system, the ANS. The HRV can be expressed through different measures obtained from a signal of RR-intervals. The aim with the thesis is to investigate how well the HRV translates into sleepiness estimation and how the experimental setup might affect the results. In this study, HRV data from 85 sleep deprived drivers was collected together with the drivers’ own ratings of their sleepiness according to the nine graded Karolinska sleepiness scale, KSS. An ANOVA test showed statistical significance for almost all of the used HRV measures when the Driver ID was set as random variable. In order to reduce the number of HRV measures, a feature selection step was performed before training a Support Vector Machine (SVM) used for classification of the data. SVM classifiers are trained to use the input features describing the data to optimize hyperplanes separating the discrete set of classes. Previous research has shown good results in using HRV for sleepiness detection, but common issues are the small data sets used and that most experiments are performed in a simulator instead of at real roads. In some cases, no sleep deprivation is used. The result from the classification in this study is a mean accuracy of around 58-59 %, mean sensitivity of 50-51 %, mean specificity of 75-76 % and mean F1 score of 50-51 % over the three classes ’Alert’, ’Getting sleepy’ and ’Sleepy’. This together with the results of the ANOVA test shows that the HRV measures performed relatively poor when used for classification of the data and that there are large inter-individual differences. This suggests the use of personalized algorithms when developing a sleepiness estimation system and an investigation regarding how other confounding factors could affect the estimation is also motivated.

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44

Maury, Pierre. "Adaptation à la sécheresse et photosynthèse chez le tournesol (helianthus annuus l. )." Toulouse, INPT, 1997. http://www.theses.fr/1997INPT011A.

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Les mecanismes impliques dans la regulation du fonctionnement photosynthetique en periode seche sont plus ou moins rapidement reversibles, perturbant le fonctionnement de la plante apres rearrosage. L'objectif du travail est d'etudier la reponse genotypique du tournesol (helianthus annuus l. ) a une acclimatation au deficit hydrique, par analyse des capacites de regulation de l'energie lumineuse, et d'assimilation du co#2, a partir de modeles biochimiques. L'acclimatation induit, chez l'hybride viki, des modifications du fonctionnement du chloroplaste. Celles-ci se traduisent apres retour a des conditions d'alimentation hydrique favorable par : i) une photosynthese nette a saturation lumineuse plus elevee resultant d'une meilleure diffusion du co#2 dans la feuille, ii) un accroissement de la photorespiration sous forts eclairements permettant de dissiper l'exces d'energie photochimique. De plus, les effets sur les photosystemes ii d'un second deficit hydrique, combines a ceux des forts eclairements, sont limites par une augmentation, rapidement reversible, de la dissipation thermique. Par contre, chez la lignee t32, ce potentiel de tolerance dynamique a la photoinhibition est altere malgre une protection permanente des structures photochimiques. Une telle reponse conduit a une reduction des capacites de la feuille a valoriser les eclairements variables. Les capacites d'exportation des trioses phosphates hors du chloroplaste sont ameliorees apres acclimatation, en liaison possible avec le role des photosynthetats dans l'ajustement osmotique observe chez ces deux genotypes. Par contre, les modifications de la repartition de l'eau dans la feuille et de l'elasticite des parois cellulaires ne semblent pas liees a l'acclimatation photosynthetique de la plante. Les mecanismes regulateurs induits par l'acclimatation apparaissent selon le genotype, orientes vers la survie ou vers l'adaptation des processus photosynthetiques a la productivite en condition seches.

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45

GAGNE, GENEVIEVE. "Variabilite de populations d'orobanche cumana - genetique de la resistance a l'orobanche chez le tournesol (helianthus annuus l. )." Clermont-Ferrand 2, 2000. http://www.theses.fr/2000CLF22186.

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L'orobanche, orobanche cumana, est une angiosperme, parasite des racines du tournesol (helianthus annuus l. ). Originaire du bassin mediterraneen, elle cause d'importants degats dans les pays producteurs excepte en france. Cinq races d'orobanche ont ete caracterisees dans les pays de l'est (elle est observee en russie des le debut du siecle) et 4 en espagne (ou elle est apparue en 1958). Ces races seraient controlees par des genes notes or. Mais l'etude de la genetique de la resistance n'est pas encore bien comprise. La capacite du pathogene a surmonter les resistances et sa facilite de dissemination en font un parasite difficile a maitriser. La lutte privilegiee passe par l'utilisation de resistances naturelles. L'objectif de ce travail est d'une part d'etudier la variabilite au niveau moleculaire et au niveau de la virulence de populations d'orobanches pour voir leur evolution et d'etudier la genetique de la resistance avec ces populations caracterisees. Huit populations d'orobanches (3 bulgares, 1 roumaine, 1 turque et 3 espagnoles) ont ete caracterisees par rapd et par aflp pour deux d'entre elles. Une population bulgare et deux populations espagnoles ont ete utilisees pour les tests de resistance sur les familles f 3 de deux croisements. L'adn des f 2 a servit au marquage moleculaire (marqueurs rflp et scar) pour localiser des genes de resistance sur la carte du tournesol par la technique des bulks et par la recherche de qtl. Une faible variabilite moleculaire intra- et inter-populations a ete trouvee (rapd et aflp apportant la meme precision). Les populations sont structurees en fonction de leur origine geographique et de leur virulence. Les populations espagnoles sont probablement issues des pays de l'est. La variabilite existant entre les populations d'orobanche pourra etre utilisee pour caracteriser les races existantes. Trois genes majeurs de resistance ainsi qu'or5 ont ete localises sur le groupe de liaison 16 de la carte genetique du tournesol. Le niveau de resistance semble dependre du genotype de tournesol et de la population d'orobanche utilises. Enfin, il apparait que la mise en place d'un differentiel sur pour caracteriser les races est necessaire aussi bien pour l'etude de la genetique que pour suivre l'evolution des races.

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46

Dräger, Nadine [Verfasser], and Achim [Akademischer Betreuer] Brauer. "Holocene climate and environmental variability in NE Germany inferred from annually laminated lake sediments / Nadine Dräger ; Betreuer: Achim Brauer." Potsdam : Universität Potsdam, 2017. http://d-nb.info/1218401508/34.

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47

Junior, Hugo Jose Tozze. "Caracterização e identificação de espécies de Colletotrichum associadas à antracnose do pimentão (Capsicum annuum) no Brasil." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/11/11135/tde-20032008-151208/.

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A antracnose é uma das doenças mais importantes do pimentão em vários países. Por muitos anos, somente C. gloeosporioides foi relatado como agente causal da antracnose desta cultura no Brasil. Entretanto, recentemente C. acutatum e C. capsici também tem sido associados a esta doença em algumas regiões do país. Neste trabalho, 56 isolados de Colletotrichum obtidos de pimentão e procedentes de diferentes regiões produtoras do país foram caracterizados e identificados por meio de algumas características morfológicas e culturais, e pela análise por PCR utilizando oligonucleotídeos espécie-específicos. Isolados representativos de cada espécie identificada na população amostrada também foram caracterizados quanto à patogenicidade em frutos de pimentão verdes e maduros, feridos e não feridos e quanto a sensibilidade aos fungicidas azoxistrobina, carbendazim, tiabendazol, tebuconazol, captana, clorotalonil e cloreto de benzalcônio. Os resultados demonstram que C. acutatum é a espécie predominante nas principais regiões produtoras de pimentão do país, representando cerca de 72% da população amostrada. C. capsici foi encontrada com freqüência aproximada de 14%, nos estados de São Paulo e Minas Gerais. C. gloeosporioides representou apenas 5% da população amostrada e teve distribuição restrita ao estado de São Paulo e ao Distrito Federal. Um único isolado de C. coccodes foi encontrado no Rio Grande do Sul. Além dessas espécies, isolados identificados como C. boninense foram encontrados em São Paulo e no Rio Grande do Sul, com freqüência de 7% na população amostrada. Este parece ser o primeiro relato de C. boninense infectando pimentão no Brasil e em outras partes do mundo. A caracterização patogênica mostrou que isolados representativos de todas as espécies foram patogênicos aos frutos maduros feridos e não feridos. Nos frutos verdes feridos, apenas os isolados de C. acutatum e de C. capsici promoveram sintomas. Não foram observados sintomas nos frutos verdes sem ferimentos durante o período de avaliação do experimento (12 dias) para nenhum dos isolados. C. acutatum demonstrou ser a espécie mais agressiva, apresentando os menores períodos de latência e a maior esporulação tanto em frutos verdes (feridos) como nos maduros (feridos e não feridos). Os isolados pertencentes a diferentes espécies de Colletotrichum apresentaram sensibilidade diferenciada para todos os fungicidas sistêmicos avaliados. Os isolados de C. acutatum foram mais sensíveis a azoxistrobina, enquanto os isolados de C. gloeosporioides demonstraram a menor sensibilidade para este fungicida. Os isolados de C. gloeosporioides e C. boninense foram os mais sensíveis aos benzimidazóis (carbendazim e tiabendazol), enquanto o isolado de C. coccodes teve a menor sensibilidade para estes fungicidas. O fungicida tebuconazol promoveu o maior controle sobre o crescimento micelial dos isolados. Para este fungicida, C. capsici demonstrou ser a espécie menos sensível. Os resultados deste trabalho demonstram a presença de pelo menos cinco espécies de Colletotrichum responsáveis pela antracnose do pimentão no país e evidenciam a presença de importantes diferenças entre essas, que devem ser consideradas durante o manejo da doença.
In several countries, anthracnose is one of the most serious diseases in pepper. C. gloeosporioides has, for many years, been reported as the causal agent of anthracnose in Brazil. C. acutatum and C. capsici have only recently been reported as agents of anthracnose in some regions of the country. In this study, 56 isolates of Colletotrichum obtained from pepper from different areas of the country were characterized and identified based on the morphological characteristics of the conidia, as well as culture characteristics and PCR analysis with species-specific pairs of primers. Isolates representative of each identified species in the sampled population were also characterized according to their pathogenicity in pepper fruits (unripe, ripe, wounded and nonwounded) and also according to their sensitivity to fungicide (azoxystrobin, carbendazim, thiabendazole, tebuconazole, captan, chlorothalonil and benzalkonium chloride). The results have showed that C. acutatum is the most prevalent species found in the main production areas of pepper, present in about 72% of the sampled population. C. capsici was equivalent to 14% of the sampled population and found in the states of São Paulo and Minas Gerais. C. gloeosporioides was present in only 5% of the samples and it was restricted to the state of São Paulo and Distrito Federal. Only one isolate of C. coccodes was found in Rio Grande do Sul. Besides theses species, isolates of C. boninense were found in São Paulo and Rio Grande do Sul, with an occurrence of 7% in the sampled population. This seems to be the first report of C. boninense infecting pepper in Brazil and other parts of the world. The pathogenic characterization showed that representative isolates of all species were pathogenic in ripe, wounded, or nonwounded fruits. In wounded green fruit, only isolates of C. acutatum and C. capsici caused infection resulting in disease symptoms. No disease symptoms were observed in green nonwounded fruits inoculated with all Colletotrichum isolates, after 12 days of inoculation. C. acutatum was the most aggressive species with the shortest periods of latency and the highest rate of sporulation in either green wounded fruits or ripe fruits (wounded and nonwounded). Isolates of different species of Colletotrichum showed different sensitivity to the systemic fungicides evaluated. The isolates of C. acutatum were more sensitive to azoxystrobin, whereas C. gloeosporioides showed the lowest sensitivity to this fungicide. C. gloeosporioides and C. boninense isolates were the most sensitive to benzimidazoles fungicides (carbendazim and thiabendazole), whereas C. coccodes isolates showed the lowest sensitivity to these fungicides. The tebuconazol fungicide exerted the highest effect on mycelial growth for all Colletotrichum species. C. capsici showed to be less sensitive to this fungicide. The results of this work have shown the presence of at least five species of Colletotrichum responsible for anthracnose in pepper in Brazil and have made evident the importance of the differences between these species, which must be taken into account for the control of the disease.

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Seviour, William J. M. "Variability of the polar stratosphere and its influence on surface weather and climate." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:ed566f6a-cc23-40c7-8237-465646058eb5.

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Research during the last two decades has established that variability of the winter polar stratospheric vortex can significantly influence the troposphere, affecting the likelihood of extreme weather events and the skill of long-range weather forecasts. This influence is particularly strong following the rapid breakdown of the vortex in events known as sudden stratospheric warmings (SSWs). This thesis addresses some outstanding issues in our understanding of the dynamics of this stratospheric variability and its influence on the troposphere. First, a geometrical method is developed to characterise two-dimensional polar vortex variability. This method is also able to identify types of SSW in which the vortex is displaced from the pole and those in which it is split in two; known as displaced and split vortex events. It shown to capture vortex variability at least as well as previous methods, but has the advantage of being easily applicable to climate model simulations. This method is subsequently applied to 13 stratosphere-resolving climate models. Almost all models show split vortex events as barotropic and displaced vortex events as baroclinic; a difference also seen in observational reanalysis data. This supports the idea that split vortex events are caused by a resonant excitation of the barotropic mode. Models show consistent differences in the surface response to split and displaced vortex events which do not project stongly onto the annular mode. However, these differences are approximately co-located with lower stratospheric anomalies, suggesting that a local adjustment to stratospheric potential vorticity anomalies is the mechanism behind the different surface responses. Finally, the predictability of the polar stratosphere and its influence on the troposphere is assessed in a stratosphere-resolving seasonal forecast system. Little skill is found in the prediction of the strength of the Northern Hemisphere vortex at lead times beyond one month. However, much greater skill is found for the Southern Hemisphere vortex during austral spring. This allows for forecasts of interannual changes in ozone depletion to be inferred at lead times much beyond previous forecasts. It is further demonstrated that this stratospheric skill descends with time and leads to an enhanced surface skill at lead times of more than three months.

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O'Donnell, Alison J., Kathryn J. Allen, Robert M. Evans, Edward R. Cook, and Valerie Trouet. "Wood density provides new opportunities for reconstructing past temperature variability from southeastern Australian trees." Elsevier B.V, 2016. http://hdl.handle.net/10150/621340.

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Tree-ring based climate reconstructions have been critical for understanding past variability and recent trends in climate worldwide, but they are scarce in Australia. This is particularly the case for temperature: only one tree-ring width based temperature reconstruction – based on Huon Pine trees from Mt Read, Tasmania – exists for Australia. Here, we investigate whether additional tree- ring parameters derived from Athrotaxis cupressoides trees growing in the same region have potential to provide robust proxy records of past temperature variability. We measured wood properties, including tree-ring width (TRW), mean density, mean cell wall thickness (CWT), and tracheid radial diameter (TRD) of annual growth rings in Athrotaxis cupressoides, a long-lived, high-elevation conifer in central Tasmania, Australia. Mean density and CWT were strongly and negatively correlated with summer temperatures. In contrast, the summer temperature signal in TRW was weakly positive. The strongest climate signal in any of the tree-ring parameters was maximum temperature in January (mid-summer; JanTmax) and we chose this as the target climate variable for reconstruction. The model that explained most of the variance in JanTmax was based on TRW and mean density as predictors. TRW and mean density provided complementary proxies with mean density showing greater high-frequency (inter-annual to multi-year) variability and TRW showing more low-frequency (decadal to centennial-scale) variability. The final reconstruction model is robust, explaining 55% of the variance in JanTmax, and was used to reconstruct JanTmax for the last five centuries (1530–2010 C.E.). The reconstruction suggests that the most recent 60 years have been warmer than average in the context of the last ca. 500 years. This unusually warm period is likely linked to a coincident increase in the intensity of the subtropical ridge and dominance of the positive phase of the Southern Annular Mode in summer, which weaken the influence of the band of prevailing westerly winds and storms on Tasmanian climate. Our findings indicate that wood properties, such as mean density, are likely to provide significant contributions toward the development of robust climate reconstructions in the Southern Hemisphere and thus toward an improved understanding of past climate in Australasia.

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Rachid, Alchaarani Ghias. "Variabilité génétique et identification des QTLs liés à la qualité des semences chez le tournesol (Helianthus annuus L. )." Toulouse, INPT, 2004. http://www.theses.fr/2004INPT002A.

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Afin de progresser dans le domaine de la sélection assistée par marqueurs moléculaires chez le tournesol, nous avons réalisé plusieurs expérimentations sur une population de lignées recombinantes (RILs) issues du croisement entre deux génotypes 'PAC-2' et 'RHA-266'. La variabilité génétique pour la résistance partielle au mildiou (Plasmopara halstedii) et à la maladie des taches noires (Phoma macdonaldii), ainsi que pour quelques caractères d'intérêt agronomique et des paramètres de la germination et du développement des plantules ont été étudiés chez les RILs et leurs parents. L'analyse de variance montre une grande variabilité entre les RILs pour la résistance partielle pour les deux maladies et les caractères d'intérêt agronomique étudiés. Afin d'identifier les QTLs contrôlant les caractères étudiés, la carte génétique construite à partir des RILs et leurs parents mentionnés ci-dessus a été améliorée en augmentant le nombre de marqueurs AFLPs et additionnant des marqueurs SSRs. Plusieurs QTLs liés aux caractères étudiés ont été identifiés. Les effet de chaque QTL sont entre 6. 4% et 20. 2% pour la résistance partielle aux deux maladies, entre 7% et 37% pour les caractères d'intérêt agronomique et entre 6% et 33% pour les paramètres de germination et de développement des plantules. Les QTLs détectés se trouvent parfois sur le même groupe de liaison les uns proches des autres et les corrélations génétiques entre les caractères confirment également cette relation. Ces régions chromosomiques devront être cartographiées de façon plus précise si l'on souhaite les utiliser dans un programme de sélection assistée par marqueurs. Afin d'augmenter la variabilité génétique par l'irradiation et la culture in vitro, les graines d'un hybride F1 et ses deux parents 'AS613' et 'AS616' ont été irradiées par sept doses de rayons (5, 15, 25, 35, 45, 55 et 66 Grays). Trois paramètres d'organogenèse ont été étudiés pour les génotypes avec les graines irradiées et les graines non irradiées (contrôle). La variabilité génétique, l'effet d'irradiation et l'interaction entre génotype-irradiation ont été déterminés pour tous les paramètres étudiés. L'irradiation des graines de l'hybride F1 par 5 et 15 Grays de rayons gamma a un effet positif sur l'augmentation de l'aptitude à la régénération par organogenèse à partir de cotylédons chez le tournesol. Les mutants induits par les deux moyens; irradiation et variation somaclonale peuvent être dans l'amélioration de cette espèce.

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Dissertations / Theses on the topic 'Annual variability'

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