David W. Wang

Surface waves traversing polar marginal ice zones (MIZs) generate a boundary layer immediately below the ice, similar in some respects to the wave boundary layer created at the seabed in shallow water. The wave–ice boundary layer has not yet been thoroughly measured, but it can significantly affect wave attenuation rates. In December 2021, we conducted a laboratory experiment designed to measure such a boundary layer and the associated attenuation, in which monochromatic waves propagated through broken surface ice in a salt water tank. A particle imaging velocimetry (PIV) instrument array was submerged in the tank and used to visualize the fluid motion under the moving ice. The surface was tracked at multiple locations with acoustic sensors and cameras mounted over the tank. A total of 64 trials were completed, each producing 3–6 s of highly resolved velocity time series and 30–40 s of surface elevation data. Preliminary analysis of the data has provided strong evidence of a boundary layer at the water–ice interface. The wave attenuation rates compare well with existing datasets. The vertical profiles of RMS velocities and wave-induced Reynolds stress have trends similar to the theoretical predictions, while the quantitative discrepancies in terms of numerical values are discussed. This is the first of two such experiments; the second is tentatively scheduled for early 2023.

We conduct a comprehensive analysis of over 350 years of accumulated ocean surface elevation time series and examine evidence for the effects of nonlinear frequency modulation, wave directional spread, surface current shear, and wind forcing on the likelihood of rogue wave development. Hourly sections of positional time series from 34 surface buoys are examined to identify over 8000 rogue wave events, recording wave sizes, times of occurrence, and geographic locations. The initial dataset is subjected to a quality control process to identify and remove false positives. We investigate the correlation of rogue events with the specified marine environmental factors in an attempt to validate the predictions of earlier theoretical and modeling analyses. The rogue event dataset is contrasted with a control, non-rogue dataset containing a total of nearly 510,000 hourly data segments of surface wave data. The analysis combines the wave records with surface current and wind data from state-of-the-art global coupled models. Statistics of the identified rogue events are summarized, and results of the environmental factor analysis are presented and discussed. This study finds some support for a causal connection between each of the environmental factors and the development of rogue waves. Results also suggest that localized environmental conditions at specific sites, such as seasonal variations in directional spread and/or high surface current vorticity, may provide useful signals of greater rogue wave threat.

Numerous studies have identified the complexities of the wave climatology around the South African coast, but limited studies have investigated these complex dynamics in the available literature. Several freely available parameterized wave boundary conditions are produced around southern Africa. However, none of these are fully spectral outputs from global or larger regional spectral wave models. This constraint results in local engineering and scientific organizations, reconstructing their own spectral boundary conditions. For coastal models, this is a reasonable assumption, assuming that the single parameterization is accurate and a representation of a non-multimodal sea state. The South African Weather Service (SAWS) Marine unit recently launched their coupled, operational wave and storm surge forecasting model. The aim of the SAWS Wave and Storm Surge (SWaSS) platform was to provide accurate, high-resolution coastal forecasts for the entire South African coastline. The present investigation thus presents the validation of the spectral wave component of the coupled system, developed in Delft3D. Various wave boundary reconstructions are investigated together with the two most used and well-known whitecapping formulations. Validation is performed with both in situ wave-rider buoy data (at nine locations along the coastline) and regional remotely sensed, along track, altimetry data. Full model performance statistics are provided, and the accuracy of the model is discussed.

Optically-active constituents vary over short time and space scales in coastal waters, and they are impacted by a variety of complex, inter-related forcing processes. As part of the Integrated Coastal Bio-Optical Dynamics (ICoBOD) project, we conducted a field campaign in Mississippi Sound in the northern Gulf of Mexico during spring 2018 to examine the impact of the passage of atmospheric and tidal fronts on fine-scale physical and bio-optical property distributions in a shallow, dynamic, coastal environment. During a 25-day experiment, we deployed eight moorings over a roughly 7 × 7 km box encompassing a frontal zone, to collect a time series of physical and bio-optical measurements. We describe changes in diver visibility related to the passage of a short-duration, high-turbidity surface plume and nepheloid layer development/decay during a tidal cycle. Maximum nepheloid layer development was observed during low tide and lasted about 9–12 h. The strongest turbidity signal extended about 4–5 m above the bottom (approximately half of the water column), although anomalously elevated values were observed all the way to the surface. In addition, high-resolution (50 m) hydrodynamic model simulations provide insight into the frontal dynamics and aid interpretation of the observed patterns. Mooring observations confirmed model-predicted heat flux changes associated with the passage of an atmospheric cold front.

Whitecap (WC) formation due to waves breaking on a wind-roughened sea surface facilitates the exchange of mass, momentum, and energy across the air–sea interface. While approximate analytical electromagnetic (EM) models paired with surface gravity wave spectra have been used to predict surface roughness emissivity enhancement, these methods do not reveal details of the response to foam, breaking wave, and WC geometry. They also ignore possible coupling between the roughness and WC emissivity effects. We report the application of a full-wave finite-difference time-domain (FDTD) EM model to investigate the separate and combined emissivity effects of specific surface roughness profiles, associated WC fields, and overlying spray. The model solves Maxwell's equations directly for an arbitrary free space and dielectric configuration. It is applied to multiple dielectric layers representing foam and spray overlying flat and rough sea surfaces. The foam layer profiles are adapted from Anguelova's L-band radiative transfer model and the rough surface is a statistical realization of the Kudryavtsev gravity wave spectrum. The model is also used to investigate the secondary effect of sea state on emissivity for a given mean square slope, which is the primary factor governing rough surface emissivity enhancement. The accuracy and precision of the FDTD model emissivity estimates and the detectability of WCs using L-band radiometry are assessed under various wind conditions, including those of tropical storm and category 1 hurricane strength. The prospects for performing Monte Carlo simulations for stronger winds and deterministic simulations of breakers with WCs of various void fractions, shapes, and scales are also considered.

It has been recognized that modulated wave groups trigger wave breaking and generate energy dissipation events on the ocean surface. Quantitative examination of wave-breaking events and associated turbulent kinetic energy (TKE) dissipation rates within a modulated wave group in the open ocean is not a trivial task. To address this challenging topic, a set of laboratory experiments was carried out in an outdoor facility, the Oil and Hazardous Material Simulated Environment Test Tank (203 m long, 20 m wide, 3.5 m deep). TKE dissipation rates at multiple depths were estimated directly while moving the sensor platform at a speed of about 0.53 m s ⁻¹ toward incoming wave groups generated by the wave maker. The largest TKE dissipation rates and significant whitecaps were found at or near the center of wave groups where steepening waves approached the geometric limit of waves. The TKE dissipation rate was O (10 ⁻² ) W kg ⁻¹ during wave breaking, which is two to three orders of magnitude larger than before and after wave breaking. The enhanced TKE dissipation rate was limited to a layer of half the wave height in depth. Observations indicate that the impact of wave breaking was not significant at depths deeper than one wave height from the surface. The TKE dissipation rate of breaking waves within wave groups can be parameterized by local wave phase speed with a proportionality breaking strength coefficient dependent on local steepness. The characterization of energy dissipation in wave groups from local wave properties will enable a better determination of near-surface TKE dissipation of breaking waves.

The influence of sea surface roughness dominates the error budget of satellite sea surface salinity (SSS) retrieval from L-band radiometers; thus, accurate roughness correction models are needed. Semi-analytical SSS correction models, as used in the soil moisture and ocean salinity satellite Level 2 processor, combine an emissivity model with an ocean wave spectrum model that describes the rough sea surface. Previous findings indicate that the errors contributed by ocean roughness model exceed those of the emissivity model. In this paper, we compare the performance of three well-known spectrum models and a new one as inputs to the small slope approximation/small perturbation method emissivity model. The new spectrum model, which is developed from empirical parameterization of short water wave spectra measured in the ocean and incorporates swell effects, performs very well in comparison with the other spectrum models, and we propose its consideration for future SSS roughness correction models.