331 research outputs found

    Proceedings of the XXVIIIth TELEMAC User Conference 18-19 October 2022

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    Hydrodynamic

    Physical Processes in Lakes

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    Physical processes are keys for the status of a lake. In this Special Issue, the emphasis is on dissolved oxygen and on exchange of gases, energy and momentum between atmosphere and further mixing and consumption within the water. The studies presented relate to ice-free as well as ice-covered lakes. Field measurements are combined with theoretical approaches

    Science at the environmental research station Schneefernerhaus / Zugspitze

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    Das Buch enthält 22 Aufsätze, in denen die in der Forschungsstation Schneefernerhaus / Zugspitze aktiven Forscherinnen und Forscher ihre Arbeitsgebiete und bisherige Ergebnisse vorstellen. Die Aufsätze sind dabei so konzipiert, dass das Buch auch für die universitäre Lehre eingesetzt werden kann

    Large scale dynamics of the atmosphere: Planetary waves

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    Planetary waves (PW) are global scale waves in the atmosphere, which are known to considerably impact weather patterns in the midlatitudes in the troposphere and the ozone distribution in the stratosphere. PW play an important role in coupling middle atmosphere dynamics. Due to the fact that climate change causes a decrease of the meridional temperature gradient, the strength of the zonal wind might decrease. This should, in turn, change the planetary wave activity (PWA). In order to quantify possible changes in the PWA we analyze ERA–Interim temperature data (10 m to 65 km height) on the Northern Hemisphere and calculate the so-called dynamical activity index (DAI) as measure for the PWA. We analyze the PWA to find indications for PWA changes and variability. We also use rotational temperature data from hydroxyl airglow measurements at UFS Schneefernerhaus (Germany) embedded in the international Network for the Detection of Mesospheric Change (NDMC) in the upper mesosphere/lower thermosphere (UMLT). We find an indication for a significant increase of the PWA in the stratosphere. The change of the PWA with higher zonal wavenumbers turns out to be strongest. This finding is in agreement with the expectation that a weakening of the meridional temperature gradient leads to improved vertical propagation conditions for planetary waves. With the empirical mode decomposition (EMD) we are able to extract non-stationary signals of the PWA time series. We further find that longer-term oscillations (QBO, ENSO and solar cycles) have a noticeable impact on the PW variability in all considered heights. Next to the 11-year cycle that is related to the sunspot-cycle in many studies, we also find a pronounced quasi-22-year signal. We tentatively interpret this signal as being due to the solar-magnetic-field (“Hale cycle”)

    Eighth International Symposium “Monitoring of Mediterranean Coastal Areas. Problems and Measurement Techniques”

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    The 8th International Symposium "Monitoring of Mediterranean Coastal Areas. Problems and Measurements Techniques" was organized by CNR-IBE in collaboration with FCS Foundation, and Natural History Museum of the Mediterranean and under the patronage of University of Florence, Accademia dei Geogofili, Tuscany Region and Livorno Province. It is the occasion in which scholars can illustrate and exchange their activities and innovative proposals, with common aims to promote actions to preserve coastal marine environment. Considering Symposium interdisciplinary nature, the Scientific Committee, underlining this holistic view of Nature, decided to celebrate Alexander von Humboldt; a nature scholar that proposed the organic and inorganic nature’s aspects as a single system. It represents a sign of continuity considering that in-presence Symposium could not be carried out due to the COVID-19 pandemic restrictions. Subjects are related to coastal topics: morphology; flora and fauna; energy production; management and integrated protection; geography and landscape, cultural heritage and environmental assets, legal and economic aspects

    Modelling, Simulation and Data Analysis in Acoustical Problems

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    Modelling and simulation in acoustics is currently gaining importance. In fact, with the development and improvement of innovative computational techniques and with the growing need for predictive models, an impressive boost has been observed in several research and application areas, such as noise control, indoor acoustics, and industrial applications. This led us to the proposal of a special issue about “Modelling, Simulation and Data Analysis in Acoustical Problems”, as we believe in the importance of these topics in modern acoustics’ studies. In total, 81 papers were submitted and 33 of them were published, with an acceptance rate of 37.5%. According to the number of papers submitted, it can be affirmed that this is a trending topic in the scientific and academic community and this special issue will try to provide a future reference for the research that will be developed in coming years

    EXPORTS Measurements and Protocols for the NE Pacific Campaign

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    EXport Processes in the Ocean from Remote Sensing (EXPORTS) is a large-scale NASA-led and NSF co-funded field campaign that will provide critical information for quantifying the export and fate of upper ocean net primary production (NPP) using satellite information and state of the art technology

    Vertical fluxes in the upper ocean

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    Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2021.Oceanic fronts at the mesoscale and submesoscale are associated with enhanced vertical motion, which strengthens their role in global biogeochemical cycling as hotspots of primary production and subduction of carbon from the surface to the interior. Using process study models, theory, and field observations of biogeochemical tracers, this thesis improves understanding of submesoscale vertical tracer fluxes and their influence on carbon cycling. Unlike buoyancy, vertical transport of biogeochemical tracers can occur both due to the movement of isopycnals and due to motion along sloping isopycnals. We decompose the vertical velocity below the mixed layer into two components in a Lagrangian frame: vertical velocity along sloping isopycnal surfaces and the adiabatic vertical velocity of isopycnal surfaces and demonstrate that vertical motion along isopycnal surfaces is particularly important at submesoscales (1-10 km). The vertical flux of nutrient, and consequently the new production of phytoplankton depends not just on the vertical velocity but on the relative time scales of vertical transport and nutrient uptake. Vertical nutrient flux is maximum when the biological timescale of phytoplankton growth matches the vertical velocity frequency. Export of organic matter from the surface and the interior requires water parcels to cross the mixed layer base. Using Lagrangian analysis, we study the dynamics of this process and demonstrate that geostrophic and ageostrophic frontogenesis drive subduction along density surfaces across the mixed layer base. Along-front variability is an important factor in subduction. Both the physical and biological modeling studies described above are used to interpret observations from three research cruises in the Western Mediterranean. We sample intrusions of high chlorophyll and particulate organic carbon below the euphotic zone that are advected downward by 100 meters on timescales of days to weeks. We characterize the community composition in these subsurface intrusions at a lateral resolution of 1–10 km. We observe systematic changes in community composition due to the changing light environment and differential decay of the phytoplankton communities in low-light environments, along with mixing. We conclude that advective fluxes could make a contribution to carbon export in subtropical gyres that is equal to the sinking flux.The work in this dissertation was funded by a NDSEG fellowship, Martin Fellowship, Grassle fellowship, Montrym grant, WHOI Academic Programs Office, and Office of Naval Research CALYPSO DRI grant N00014-16-1-3130

    Wave Propagation and Source Localization in Random and Refracting Media

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    This thesis focuses on understanding the way that acoustic and electromagnetic waves propagate through an inhomogeneous or turbulent environment, and analyzes the effect that this uncertainty has on signal processing algorithms. These methods are applied to determining the effectiveness of matched-field style source localization algorithms in uncertain ocean environments, and to analyzing the effect that random media composed of electrically large scatterers has on propagating waves. The first half of this dissertation introduces the frequency-difference autoproduct, a surrogate field quantity, and applies this quantity to passive acoustic remote sensing in waveguiding ocean environments. The frequency-difference autoproduct, a quadratic product of frequency-domain complex measured field values, is demonstrated to retain phase stability in the face of significant environmental uncertainty even when the related pressure field’s phase is as unstable as noise. This result demonstrates that a measured autoproduct (at difference frequencies less than 5 Hz) that is associated with a pressure field (measured in the hundreds of Hz) and which has propagated hundreds of kilometers in a deep ocean sound channel can be consistently cross-correlated with a calculated autoproduct. This cross-correlation is shown to give a cross-correlation coefficient that is more than 10 dB greater than the equivalent cross-correlation coefficient of the measured pressure field, demonstrating that the autoproduct is a stable alternative to the pressure field for array signal processing algorithms. The next major result demonstrates that the frequency-difference autoproduct can be used to passively localize remote unknown sound sources that broadcast sound hundreds of kilometers to a measuring device at hundreds of Hz frequencies. Because of the high frequency content of the measured pressure field, an equivalent conventional localization result is not possible using frequency-domain methods. These two primary contributions, recovery of frequency-domain phase stability and robust source localization, represent unique contributions to existing signal processing techniques. The second half of this thesis focuses on understanding electromagnetic wave propagation in a random medium composed of metallic scatterers placed within a background medium. This thesis focuses on developing new methods to compute the extinction and phase matrices, quantities related to Radiative Transfer theory, of a random medium composed of electrically large, interacting scatterers. A new method is proposed, based on using Monte Carlo simulation and full-wave computational electromagnetics methods simultaneously, to calculate the extinction coefficient and phase function of such a random medium. Another major result of this thesis demonstrates that the coherent portion of the field scattered by a configuration of the random medium is equivalent to the field scattered by a homogeneous dielectric that occupies the same volume as the configuration. This thesis also demonstrates that the incoherent portion of the field scattered by a configuration of the random medium, related to the phase function of the medium, can be calculated using buffer zone averaging. These methods are applied to model field propagation in a random medium, and propose an extension of single scattering theory that can be used to understand mean field propagation in relatively dense (tens of particles per cubic wavelength) random media composed of electrically large (up to 3 wavelengths long) conductors and incoherent field propagation in relatively dense (up to 5 particles per cubic wavelength) media composed of electrically large (up to two wavelengths) conductors. These results represent an important contribution to the field of incoherent, polarimetric remote sensing of the environment.PHDApplied PhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/169886/1/geroskdj_1.pd
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