Sea-level change over the northern European continental shelf due to atmospheric and oceanic contributions

Global mean sea level (GMSL) is a key indicator of climate change as it comprises information on different components of the climate system. However, despite its importance for climate and society, GMSL cannot be used for coastal adaptation policies because regional sea-level variations can significantly depart from the global average. Providing accurate estimates of sea-level rise is therefore one of the most important scientific issues that climate change poses, with a large impact for the human population as it is recognized as the main driver for changes in sea-level extremes, influencing the non-linear interactions between processes acting over different temporal and spatial scales in coastal areas. This thesis addresses different aspects of the sea-level variability over the northern European continental shelf. Paper I uses gridded satellite altimetry data and adopts the jet clusters perspective of the winter-time atmospheric variability over the North Atlantic to reassess the contribution of local winds to the sea-level variability over the northern European continental shelf. By using the jet clusters, Paper I distinguishes itself from the existing literature since the jet clusters provide a physical description of the atmospheric variability in the North Atlantic. Papers II and III focus on the steric and manometric components of the sea-level over the Norwegian section of the northern European continental shelf and on the sea-level observing system in the region. Paper II first evaluates a coastal altimetry dataset, reprocessed with the ALES-retracker, against the Norwegian set of tide gauges. After showing a good agreement between the two, it exploits the coastal satellite altimetry dataset to reassess the steric component of the sea level over the Norwegian shelf: the paper finds that the estimates of the steric component of the sea-level do not depend much on the choice of the tide gauges or satellite altimetry. Paper III evaluates the sea-level observing system along the Norwegian coast by assessing the ability of a satellite gravimetry mission, the Gravity Recovery and Climate Experiment (GRACE), and of a combination of satellite altimetry and hydrography to monitor manometric sea-level variations in the region. It then investigates the open-ocean contribution to the inter-annual manometric sea-level variations along the coast of Norway. It shows that, while commonly considered not reliable in the coastal region, GRACE captures the main features of the manometric sea-level change in the area, which on interannual and longer time scales can be attributed to along-slope winds and open-ocean steric changes. Therefore, GRACE can be used to analyze the manometric sea-level variability, such as in sea-level budget studies, especially in those areas of the coastal ocean where in-situ measurements are sparse. Overall, by focusing on the northern European continental shelf due to its well developed sea-level observing system, this thesis has demonstrated the potential of remote sensing observations in improving our understanding of sea-level variability and change in the coastal ocean.Doktorgradsavhandlin

Interazione elettromagnetica da oggetti sepolti o immersi

Interazione elettromagnetica da oggetti sepolti o immers

Statistics of modal condensation in nonlinear multimode fibers

Optical pulses propagating in multimode optical fibers are affected by linear disorder and nonlinearity, and experience chaotic exchange of power among modes. On the other hand, complex systems can attain steady states characterized by energy condensation into single as well multiple sub-systems. In this work, we study beam propagation in multimode optical fibers in the presence of linear random mode coupling and Kerr nonlinearity; both effects lead to a mode power redistribution at the fiber output. We use a new 3D mode decomposition method to obtain, with unprecedented accuracy, measurements of the modal distribution from long spans of graded-index fiber; we perform numerical simulations using a new model for the linear disorder; we introduce a weighted Bose-Einstein law and show that it is suitable for describing steady-state modal power distributions both in the linear and nonlinear regimes. We show that, at power levels intermediate between the linear and the soliton regimes, energy condensation is attained locally by the second, third and fourth modal groups, before global condensation to the fundamental mode is reached in the soliton regime. Our results extend the thermodynamic approach to multimode fibers to unexplored optical states, which acquire the characteristics of optical glass.Comment: 25 pages, 8 figure

Electromagnetic Scattering by a Cylinder in a Lossy Medium of an Inhomogeneous Elliptically Polarized Plane Wave, Journal of Telecommunications and Information Technology, 2019, nr 4

In this paper, a rigorous theoretical approach, adopted in order to generalize the Vectorial CylindricalHarmonics (VCH) expansion of an inhomogeneous elliptically polarized plane wave, is presented. An application of the VCH expansion to analyze electromagnetic field scattered by an infinite circular cylinder is presented. The results are obtained using the so-called complex-angle formalism reaching a superposition of Vectorial Cylindrical-Harmonics. To validate the method, a Matlab code was implemented. Also, the validity of the methodology was confirmed through some comparisons between the proposed method and the numerical results obtained based on the Finite Element Method (FEM) in the canonical scenario with a single cylinde

Erratum: "Cloaking using anisotropic multilayer circular cylinder" [AIP Adv. 10, 095312 (2020)]

n/

Detection of a misaligned broken pipe by electromagnetic interaction

The study we are presenting concerns electromagnetic scattering of a plane wave due to the presence of a misaligned broken pipe buried in a half-space occupied by cement and by asphalt/ground, for civil-engineering applications

The dependence of minimum-time routes over the North Atlantic on cruise altitude

North Atlantic air traffic is broadly organised into a track system; daily sets of tracks are defined by air traffic control which are vertically stacked, such that the same set of tracks is used for all flight levels, regardless of any vertical variations in wind. This work uses minimum-time routes, previously shown to be a good proxy for the location of the North Atlantic track system, to understand whether vertical variations in wind speed and direction significantly affect minimum-time routes optimised at different altitudes; this is to examine whether (all other factors assumed equal) there is potential for improvements in fuel efficiency. The optimum cruise altitude over the North Atlantic is determined, focusing on the New York – London route. It is found that eastbound routes, which take advantage of the jet stream, are on average faster at 250 hPa (flight level (FL) 340) than at 300 hPa (FL300) or 200 hPa (FL390) by approximately 2 minutes (compared to the annual-mean route time of about 330 minutes, assuming a true air speed of 250 m s-1). For westbound routes, the route time increases with height: aircraft flying at 300 hPa are on average 3 minutes faster than at higher levels (the annual-mean optimum time being about 400 minutes). These estimates are compared with the time penalty which arises from flying a route optimized at 250 hPa at the other two altitudes. The time penalty is generally less than a minute, compared to the minimum-time routes calculated at those altitudes

Nonlinear beam self-imaging and self-focusing dynamics in a GRIN multimode optical fiber: theory and experiments

Beam self-imaging in nonlinear graded-index multimode optical fibers is of interest for many applications, such as implementing a fast saturable absorber mechanism in fiber lasers via multimode interference. We obtain an exact solution for the nonlinear evolution of first and second order moments of a laser beam carried by a graded-index multimode fiber, predicting that the spatial self-imaging period does not vary with power. Whereas the amplitude of the oscillation of the beam width is power-dependent. We have experimentally studied the longitudinal evolution of beam self-imaging by means of femtosecond laser pulse propagation in both the anomalous and the normal dispersion regime of a standard telecom graded-index multimode optical fiber. Light scattering out of the fiber core via visible fluorescence emission and harmonic wave generation permits us to directly confirm that the self-imaging period is invariant with power. Spatial shift and splitting of the self-imaging process under the action of self-focusing are also emphasized

Analysis of storm surge events along the Norwegian coast

Observed extreme sea levels are caused by a combination of extreme astronomical tide and extreme storm surge, or by an extreme value in one of these variables and a moderate value in the other. We analyzed measurements from the Norwegian tide gauge network together with storm track data to assess cases of extreme sea level and storm surges. At most stations the highest storm surges only coincided with moderate astronomical tides and vice versa. Simultaneously the extreme storm surges often only coincided with moderate storm intensities. This opens for the possibility of flooding events, where extreme tides and storm surges co-occur, and which could exceed existing sea level records and national building standards. This study also raises the possibility to assess extreme sea level return values as a three-variable system, treating separately the astronomical tide, storm location and storm intensity, instead of the one- or two-variable approach currently used.publishedVersio

Multimode soliton collisions in graded-index optical fibers

In thiswork, we unveil the unique complex dynamics of multimode soliton interactions in graded-index optical fibers through simulations and experiments. By generating two multimode solitons from the fission of an input femtosecond pulse, we examine the evolution of their Ramaninduced red-shift when the input pulse energy grows larger. Remarkably, we find that the output red-shift of the trailing multimode soliton may be reduced, so that it accelerates until it collides with the leading multimode soliton. As a result of the inelastic collision, a significant energy transfer occurs between the two multimode solitons: the trailing soliton captures energy from the leading soliton, which ultimately enhances its red-shift, thus increasing temporal separation between the two multimode solitons