134 research outputs found
Matlab code and data to reproduce the figures used in the manuscript
No full textMatlab code and data to reproduce the figures used in the manuscript:
Streßer, M., Seemann, J., Carrasco, R., Cysewski, M., Horstmann, J., Baschek, B., & Deane, G. (2021). On the Interpretation of Coherent Marine Radar Backscatter from Surf Zone Waves. Manuscript submitted for publication.
The Mathworks Matlab software with Signal Processing and Image Processing Toolboxes are required to run the code.
External functions:
Yong Hoon Lee (2021). HCPARULA: High Contrast Parula-like Colormap Generator (https://www.mathworks.com/matlabcentral/fileexchange/61768-hcparula-high-contrast-parula-like-colormap-generator), MATLAB Central File Exchange. Retrieved March 29, 2021.
Yair Altman (2021). export_fig (https://github.com/altmany/export_fig/releases/tag/v3.14), GitHub. Retrieved March 29, 2021.
Carlos Adrian Vargas Aguilera (2021). imagescnan.m v2.1 (Aug 2009) (https://www.mathworks.com/matlabcentral/fileexchange/20516-imagescnan-m-v2-1-aug-2009), MATLAB Central File Exchange. Retrieved March 29, 2021
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Dynamics of a Submesoscale Surface Ocean Density Front
No full textSmall-scale ocean flows have increasingly ageostrophic dynamics that are important for the ocean energy budget and biogeochemical cycles. Numerical models indicate that the ageostrophic flow and vertical velocities associated with frontogenesis are a dominant mechanism of surface to interior ocean material transport. The increasingly unbalanced flow may also provide a pathway to downscale energy from the mesoscale to microscale.In situ observations of these flows are challenging due to the characteristics of the flow, such as small spatial scales and short lifetimes of hours to days. To observe the physical properties, generation, and evolution of these features, a new experimental method was developed at UCLA that incorporates simultaneous sampling by remote sensing and in situ instruments onboard satellites, aircraft, and vessels.On April 14, 2011, a small-scale frontal feature confined to the upper 10 m of the water column was measured near Catalina Island, California. The front had a maximum horizontal temperature gradient of 0.0031℃ m-1 and slope of 0.0146. To our knowledge, this is the first time such high resolution and comprehensive in situ observations have been made of submesoscale features
Occurrence and Energy Dissipation of Breaking Surface Waves in the Nearshore Studied with Coherent Marine Radar
No full textWave breaking influences air-sea interactions, wave induced forces on coastal structures, sediment transport and associated coastline changes. A good understanding of the process and a proper incorporation of wave breaking into earth system models is crucial for a solid assessment of the impacts of climate change and human influences on coastal dynamics. However, many aspects are still poorly understood which can be attributed to the fact that wave breaking is difficult to observe and study because it occurs randomly and involves multiple spatial and temporal scales.
Within this doctoral work, a nearshore field experiment was planned and conducted on the island of Sylt in the North Sea to investigate the dynamics of wave breaking. The study combines in-situ observations, numerical simulations and remote sensing using shore-based coherent marine radar. The field measurements are used to investigate the coherent microwave backscatter from shoaling and breaking waves. Three major developments result from the study. The first one is a forward model to compute the backscatter intensity and Doppler velocity from known wave kinematics. The second development is a new classification algorithm to identify dominant breakers, whitecaps and radar imaging artifacts within the radar raw data. The algorithm is used to infer the fraction of breaking waves over a sub- and an inter-tidal sandbar as well as whitecap
statistics and results are compared to different parameterizations available in literature. The third development is a new method to deduce the energy of the surface roller
from the Doppler velocity measured by the radar. The roller energy is related to the dissipation of roller energy by the stress acting at the surface under the roller. From
the spatial gradient of roller energy, the transformation of the significant wave height is computed along the entire cross-shore transect. Comparisons to in-situ measurements
of the significant wave height from two bottom mounted pressure gauges and a wave rider buoy show a total root-mean-square-error of 0.20 m and a bias of −0.02 m.
It is the first time that measurements of the spatio-temporal variation of the bulk wave energy dissipation together with the fraction of breaking waves are achieved in
storm conditions over such a large distance of more than one kilometer. The largest dissipation rates (> 300 W/m² ) take place on a short distance of less than one wave
length (≈ 50 m) at the inter-tidal sandbar. However, during storm conditions 50 % of the incoming wave energy flux is already dissipated at the sub-tidal sandbar. The
simultaneous measurements of the occurrence frequency and the energy dissipation facilitate an assessment of the bulk dissipation of individual breaking waves. For the
spilling-type breakers in this area, the observed dissipation rate is about 30 % smaller than the dissipation rate according to the generally used bore analogy. This must be
considered within nearshore wave models if accurate predictions of the breaking probability are required
Untersuchung der Blütendynamik und der ökologischen Rolle des Dinoflagellaten Noctiluca scintillans
No full textThis thesis investigates the ecological role, bloom dynamics, and spatiotemporal distribution of the harmful algal bloom-forming species Noctiluca scintillans, which adversely impacts food webs, ecosystem productivity, aquaculture, and tourism. With an extensive literature review (1857–2023), the potential global expansion of N. scintillans and its associated environmental factors are described. The analysis shows that N. scintillans has increased over time in coastal regions of Australia, China, and Europe, including the North Sea, with eutrophication, ocean warming, and deoxygenation identified as potential key drivers of these intensifications. To validate these findings and identify drivers as well as spatiotemporal hotspots of N. scintillans in the rapidly warming North Sea, two long-term, high-resolution time series (Helgoland Roads and Continuous Plankton Recorder survey) were analysed. Results reveal that N. scintillans abundances and bloom durations increased significantly after the 1990s, with hotspots identified near the Elbe and Rhine river estuaries. Following the identification of these hotspots, sampling campaigns were carried out in summer 2022 near Helgoland to study an entire N. scintillans bloom. Innovative imaging tools provided novel insights into its ecological role. Heavy predation on diatoms and its function as a significant recycler of phosphate and ammonium, followed by an increase in nutrient-affine dinoflagellates, suggest an important role for N. scintillans within plankton communities. This thesis underscores the value of long-term time series and advanced methodologies in understanding and predicting N. scintillans trends. The research contributes to mitigating the economic and societal impacts of these blooms on aquaculture, fisheries, and tourism in rapidly changing ecosystems
Air-sea gas exchange in tidal fronts
No full textStrong tidal currents in the Fraser Estuary, BC, Canada, cause intense flow-topography interaction around islands and over shallow sills. At Boundary Pass, a steep sill forms a pronounced barrier for flow of dense water from the Pacific Ocean into the Strait of Georgia. The processes at the sill control the renewal of deep and intermediate water in the Strait.
The strong flood tidal flow forces dense water to flow over the sill. It then meets a fresh surface layer just downstream of the sill crest and subducts underneath the fresh water, setting up a hydraulic sill flow with an arrested upper layer. Vertical current speeds at the downstream side of the sill reach up to 0.75 m s−1, and intense detrainment of dense water from the lower into the upper layer causes a volume loss of 60% over a distance of 200 m.
Surface waves travelling into the convergence zone (tidal front) over the sill crest tend to steepen and break due to wave-current interaction. The breaking waves inject gas bubbles, which either rise back to the sea surface or dissolve completely, depending on their rise speed and the strength of the vertical currents. Bubbles injected close to the plunge point of the dense water mass are drawn down by the extreme currents to depths of up to 160 m, enhancing air-sea gas exchange.
The hydraulic flow, wave-current interaction, and gas bubble behaviour are described with simple models. They are used to interpret extensive ship-board measurements during two cruises in the Fraser estuary and help in the understanding of the physical processes involved in air-sea gas exchange in tidal fronts. The oxygen flux in the tidal front at Boundary Pass is compared with other oxygen sources in the Fraser Estuary and shows that tidal fronts may contribute significantly to the aeration of an estuary.
The described processes may be also applicable to other coastal areas with strong tidal currents like Norway, Chile, or Japan, and may be important in convergence zones like deep convection regimes.Graduat
The shoelace book: a mathematical guide to the best (and worst) ways to lace your shoes
No full textCrisscross, zigzag, bowtie, devil, angel, or star: which are the longest, the shortest, the strongest, and the weakest lacings? Pondering the mathematics of shoelaces, the author paints a vivid picture of the simple, beautiful, and surprising characterizations of the most common shoelace patterns. The mathematics involved is an attractive mix of combinatorics and elementary calculus. This book will be enjoyed by mathematically minded people for as long as there are shoes to lace. Burkard Polster is a well-known mathematical juggler, magician, origami expert, bubble-master, shoelace charmer, a
Rogue Wave Observations Off the US West Coast
No full textRogue waves can cause significant damage to vessels and offshore structures and are linked to the loss of hundreds of lives at sea. They represent extreme statistical events with wave heights exceeding twice the significant wave height. The authors investigated a wave buoy data set collected off the US West Coast with 7,157 rogue waves observed over a total of 80 years. It yields comprehensive statistics regarding the likelihood of rogue wave occurrence in the open ocean, coastal ocean, and shallow water. The highest recorded rogue wave had a trough-to-crest height of 18.95 m. The average likelihood of occurrence is 63 per year in coastal waters and 101 per year in the open ocean. An extrapolation to conditions in the world ocean yields an average likelihood of encountering rogue waves along the main shipping routes in the North Atlantic of 0.8–1.2% per day for rogue waves exceeding 11 m in height. The results can be used to test rogue wave forecasting models and will help to improve the forecasting of hazardous ocean conditions
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