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

Wave-Breaking Turbulence in the Ocean Surface Layer

AbstractObservations of winds, waves, and turbulence at the ocean surface are compared with several analytic formulations and a numerical model for the input of turbulent kinetic energy by wave breaking and the subsequent dissipation. The observations are generally consistent with all of the formulations, although some differences are notable at winds greater than 15 m s−1. The depth dependence of the turbulent dissipation rate beneath the waves is fit to a decay scale, which is sensitive to the choice of vertical reference frame. In the surface-following reference frame, the strongest turbulence is isolated within a shallow region of depths much less than one significant wave height. In a fixed reference frame, the strong turbulence penetrates to depths that are at least half of the significant wave height. This occurs because the turbulence of individual breakers persists longer than the dominant period of the waves and thus the strong surface turbulence is carried from crest to trough with the wave orbital motion.</jats:p

Enhanced Leak Detection

A key requirement for Veeder-Root’s Enhanced Leak Detection System is that it be able to test in situ for the presence of leaks at gasoline dispensing facilities. Aside from the obvious issues of safety and lost product, this functionality is obligatory for compliance with environmental standards mandated by federal and state oversight bodies, such as the California State Water Resources Control Board (SWRCB). The SWRCB demands a testing procedure that includes conditions as close to operational as possible, while still using environmentally safe gases as a test fluid. Although the test parameters (e.g., pressure) are allowed to deviate from operating conditions in order to facilitate the test procedure, a prescribed rescaling of the test thresholds must then be applied to account for the deviation. Whether the test is run at operation conditions or in a slightly different parameter regime, the fact that the testing must be done on the product and return lines after installation at a service station presents significant challenges in devising an effective test strategy

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

A downslope propagating thermal front over the continental slope

In the ocean, internal frontal bores above sloping topography have many appearances,depending on the local density stratification, and on the angle and source of generation of the carrier wave.However, their common characteristics are a backward breaking wave, strong sediment resuspension, andrelatively cool (denser) water moving more or less upslope underneath warm (less dense) water. In thispaper, we present a rare example of a downslope moving front of cold water moving over near-bottomwarm water. Large backscatter is observed in the downslope moving front’s trailing edge, rather than theleading edge as is common in upslope moving fronts. Time series observations have been made during afortnight in summer, using a 101 m long array of high-resolution temperature sensors moored with anacoustic Doppler current profiler at 396 m depth in near-homogeneous waters, near a small canyon in thecontinental slope off the Malin shelf (West-Scotland, UK). Occurring between fronts that propagate upslopewith tidal periodicity, the rare downslope propagating one resembles a gravity current and includes strongconvective turbulence coming from the interior rather than the more usual frictionally generated turbulencearising from interaction with the seabed. Its turbulence is 3–10 times larger than that of more commonupslope propagating fronts. As the main turbulence is in the interior with a thin stratified layer close tothe bottom, little sediment is resuspended by a downslope propagating front. The downslope propagatingfront is suggested to be generated by oblique propagation of internal (tidal) waves and flow over a nearbyupstream promontory

Semi-empirical dissipation source functions for ocean waves: Part I, definition, calibration and validation

New parameterizations for the spectra dissipation of wind-generated waves are proposed. The rates of dissipation have no predetermined spectral shapes and are functions of the wave spectrum and wind speed and direction, in a way consistent with observation of wave breaking and swell dissipation properties. Namely, the swell dissipation is nonlinear and proportional to the swell steepness, and dissipation due to wave breaking is non-zero only when a non-dimensional spectrum exceeds the threshold at which waves are observed to start breaking. An additional source of short wave dissipation due to long wave breaking is introduced to represent the dissipation of short waves due to longer breaking waves. Several degrees of freedom are introduced in the wave breaking and the wind-wave generation term of Janssen (J. Phys. Oceanogr. 1991). These parameterizations are combined and calibrated with the Discrete Interaction Approximation of Hasselmann et al. (J. Phys. Oceangr. 1985) for the nonlinear interactions. Parameters are adjusted to reproduce observed shapes of directional wave spectra, and the variability of spectral moments with wind speed and wave height. The wave energy balance is verified in a wide range of conditions and scales, from gentle swells to major hurricanes, from the global ocean to coastal settings. Wave height, peak and mean periods, and spectral data are validated using in situ and remote sensing data. Some systematic defects are still present, but the parameterizations yield the best overall results to date. Perspectives for further improvement are also given.Comment: revised version for Journal of Physical Oceanograph