Dynamical and statistical explanations of observed occurrence rates of rogue waves

Extreme surface waves occur in the tail of the probability distribution. Their occurrence rate can be displayed effectively by plotting ln(–ln <i>P</i>), where <i>P</i> is the probability of the wave or crest height exceeding a particular value, against the logarithm of that value. A Weibull distribution of the exceedance probability, as proposed in a standard model, then becomes a straight line. Earlier North Sea data from an oil platform suggest a curved plot, with a higher occurrence rate of extreme wave and crest heights than predicted by the standard model. The curvature is not accounted for by second order corrections, non-stationarity, or Benjamin-Feir instability, though all of these do lead to an increase in the exceedance probability. Simulations for deep water waves suggest that, if the waves are steep, the curvature may be explained by including up to fourth order Stokes corrections. Finally, the use of extreme value theory in fitting exceedance probabilities is shown to be inappropriate, as its application requires that not just <i>N</i>, but also ln<i>N</i>, be large, where <i>N</i> is the number of waves in a data block. This is unlikely to be adequately satisfied

Immunodetection of overwintering Oidium mycelium in bud scales of Vitis vinifera

Research NoteAntigens were isolated from the walls of Oidium conidia by a simple extraction method. Polyclonal antiserum was produced against these antigens and an immunofluorescent assay was developed to detect overwintering mycelium of Oidium in dormant buds. The results show that a specific detection of Oidium mycelium is possible without visualizing other fungal mycelia in dormant buds of grapevines

FOWD: A Free Ocean Wave Dataset for Data Mining and Machine Learning

The occurrence of extreme (rogue) waves in the ocean is for the most part still shrouded in mystery, as the rare nature of these events makes them difficult to analyze with traditional methods. Modern data mining and machine learning methods provide a promising way out, but they typically rely on the availability of massive amounts of well-cleaned data. To facilitate the application of such data-hungry methods to surface ocean waves, we developed FOWD, a freely available wave dataset and processing framework. FOWD describes the conversion of raw observations into a catalogue that maps characteristic sea state parameters to observed wave quantities. Specifically, we employ a running window approach that respects the non-stationary nature of the oceans, and extensive quality control to reduce bias in the resulting dataset. We also supply a reference Python implementation of the FOWD processing toolkit, which we use to process the entire CDIP buoy data catalogue containing over 4 billion waves. In a first experiment, we find that, when the full elevation time series is available, surface elevation kurtosis and maximum wave height are the strongest univariate predictors for rogue wave activity. When just a spectrum is given, crest-trough correlation, spectral bandwidth, and mean period fill this role

Internal wave band eddy fluxes above a continental slope

Three weeks of velocity and temperature measurements from the bottom 45 m above the continental slope in the Bay of Biscay are used to evaluate the role of the internal wave band in boundary mixing near a sloping bottom. Utilizing acoustic Doppler current profilers and thermistor strings, internal wave band eddy fluxes of momentum and heat are estimated. The instrumentation is specifically designed to resolve internal wave band processes. Due to unresolved Doppler shifting, this wave band may include turbulence as well as internal waves. A very energetic and highly variable near-bottom environment is found. Periods of mixing and restratification alternate at the M2 tidal frequency. Interpreting the observations in an Ekman sense, the three-week mean current is downwelling-favorable, which is consistent with existing boundary layer theories. However, a bi-directional flow associated with sloping boundary mixing is not found in the near-bottom layer, possibly due to observed strong stratification all the way to the bottom. We evaluated boundary layer dynamics and the effect of internal wave-band fluxes from two frequency ranges (σ ≥ 15 cpd and σ ≥ 1.9 cpd, including tides) on the three-week mean flow. The high-frequency range (σ ≥ 15 cpd) of the internal wave band supports significant momentum and buoyancy fluxes while the low-frequency range (σ ≥ 1.9 cpd) only supports significant momentum fluxes. Mean bottom-normal eddy diffusivities associated with anisotropic, nonlinear internal waves, are negative and O (-10-2 m2s-1). Interpreting these negative eddy diffusivities as indication of a restratification process, high mixing efficiencies are expected throughout the mixing layer, which extends typically 20 m above the bottom. Mean eddy viscosities are positive in cross-slope direction and negative in alongslope direction, implying a strong anisotropy in the interaction between internal wave band eddies and the mean flow. Alongslope momentum is transferred from the internal tide to the mean flow. Buoyancy and pressure gradient forces, which we could not determine directly, may generate a buoyancy-driven secondary flow. The buoyancy equation is dominated by advection, possibly balanced by divergence of cross-slope and alongslope internal wave band fluxes

Convergence analysis of a multigrid algorithm for the acoustic single layer equation

We present and analyze a multigrid algorithm for the acoustic single layer equation in two dimensions. The boundary element formulation of the equation is based on piecewise constant test functions and we make use of a weak inner product in the multigrid scheme as proposed in \cite{BLP94}. A full error analysis of the algorithm is presented. We also conduct a numerical study of the effect of the weak inner product on the oscillatory behavior of the eigenfunctions for the Laplace single layer operator

Detection of grapevine fenleaf virus (GFLV) in infected grapevines by non-radioactive nucleic acid hybridisation

The nucleic acid hybridisation technique was adopted for the detection of grapevine fanleaf virus (GFLV) in grapevine tissues using a nonradioactive labeled cDNA. In crude plant sap a certain detection was not successful. Thus, a method was developed for the extraction of total RNA from a large number of samples in a microscale. By Northern blot hybridisation and by the more convenient slot blot technique GFLV infections could be detected. Comparing ELISA and slot blot hybridisation assay using identical plant material different results were obtained with some samples. This indicates different detection spectra for both techniques. The hybridisation assay has been found to be a suitable method by which a large number of samples from different grapevine tissues could be efficiently indexed for GFLV

Exploring the Arctic: An Awareness Experiment in Science Journalism and Personal Narrative

Journalism coverage of the Canadian Arctic is limited and often inconsequential, or inaccessible to the broader public due to highly specialized content, e.g. information locked in scientific papers. This is despite the fact that the Arctic is of national as well as global importance. This discrepancy may be attributed to a general deficit of journalism coverage of climate issues, which are closely linked to the Arctic region. Furthermore, as a remote and unique location, an “out of sight, out of mind” mentality both physically and conceptually removes the region from public awareness. Very few non-Arctic residents are able to experience the region first-hand, and the true vividness of the area is often lost in traditional scientific publications. However, innovations in digital storytelling and narrative could open the Arctic to increased awareness, thereby bringing climate and polar science to the forefront of tomorrow’s journalism. This Research-Creation Project combined in-person experiences on a scientific Arctic cruise with traditional reporting methods to create a catalogue of innovative multimedia pieces in a dedicated online Story Hub. Inspired by the works of Robin Wall Kimmerer and the ideas of Randy Olson, the project aimed to increase the awareness of the region with approachable and engaging narratives, sharing knowledge and personal observations through storytelling. Designed to foster passion and interest, not scientific expertise, the Research-Creation Project is a blueprint for interweaving scientific journalism with personal narrative reporting as a stepping stone to more in-depth science communication