Observations of strongly modulated surface wave and wave breaking statistics at a submesoscale front

Ocean submesoscale currents, with spatial scales on the order of 0.1 to 10 km, are horizontally divergent flows, leading to vertical motions that are crucial for modulating the fluxes of mass, momentum and energy between the ocean and the atmosphere, with important implications for biological and chemical processes. Recently, there has been considerable interest in the role of surface waves in modifying frontal dynamics. However, there is a crucial lack of observations of these processes, which are needed to constrain and guide theoretical and numerical models. To this end, we present novel high resolution airborne remote sensing and in situ observations of wave-current interaction at a submesoscale front near the island of O’ahu, Hawaii. We find strong modulation of the surface wave field across the frontal boundary, including enhanced wave breaking, that leads to significant spatial inhomogeneities in the wave and wave breaking statistics. The non-breaking (i.e. Stokes) and breaking induced drifts are shown to be increased at the boundary by approximately 50% and an order of magnitude, respectively. The momentum flux from the wave field to the water column due to wave breaking is enhanced by an order of magnitude at the front. Using an orthogonal coordinate system that is tangent and normal to the front, we show that these sharp modulations occur over a distance of several meters in the direction normal to the front. Finally, we discuss these observations in the context of improved coupled models of air-sea interaction at a submesoscale front.

The annual cycle of the error of radioaltimetric measurements of the Black Sea level due to the nonlinearity of sea waves.

The variability of the error of the altimetric determination of the Black Sea level L due to the nonlinearity of sea waves is analyzed. The nonlinearity leads to deviations in the distribution of elevations of the reflecting radio wave surface from the Gaussian distribution. The error occurs due to the fact that the median of the non-Gaussian distribution of surface elevations does not coincide with the average surface level. The analysis is carried out within the framework of the Brown model, which describes the shape of an altimetric pulse reflected from the sea surface. Data from a numerical operational model of the surface wave field are used for the analysis. When calculating the shape of the reflected pulse of the altimeter, an additional predictor is introduced – the steepness of the waves. It is shown that there is a clearly defined annual variation of the error L. Its highest values are observed in winter, when the average monthly value reaches the level of 0.25 m, in summer this error decreases to 0.08-01 m. The maximum value calculated from the three-hour characteristics of surface waves is 0.4 m, the average value is 0.17 m.

WIFF1.0: A hybrid machine-learning-based parameterization of Wave-Induced sea-ice Floe Fracture

Ocean surface waves play an important role in maintaining the marginal ice zone, a heterogenous region occupied by sea ice floes with variable horizontal sizes. The location, width, and evolution of the marginal ice zone is determined by the mutual interaction of ocean waves and floes, as waves propagate into the ice, bend it, and fracture it. In previous work, we developed a one-dimensional “superparameterized” scheme to simulate the interaction between the stochastic ocean surface wave field and sea ice. As this method is computationally expensive and not bitwise reproducible, here we use a pair of neural networks to accelerate this parameterization, delivering an adaptable, computationally-inexpensive, reproducible approach for simulating stochastic wave-ice interactions. Implemented in the sea ice model CICE, this accelerated code reproduces global statistics resulting from the full wave fracture code without increasing computational overheads. The combined model, Wave-Induced Floe Fracture (WIFF v1.0) is publicly available and may be incorporated into climate models that seek to represent the effect of waves fracturing sea ice.

Near-Resonant Regimes of a Moving Load on a Pre-Stressed Incompressible Elastic Half-Space

The article is concerned with the analysis of the problem for a concentrated line load moving at a constant speed along the surface of a pre-stressed, incompressible, isotropic elastic half-space, within the framework of the plane-strain assumption. The focus is on the near-critical regimes, when the speed of the load is close to that of the surface wave. Both steady-state and transient regimes are considered. Implementation of the hyperbolic–elliptic asymptotic formulation for the surface wave field allows explicit approximate solution for displacement components expressed in terms of the elementary functions, highlighting the resonant nature of the surface wave. Numerical illustrations of the solutions are presented for several material models.

The Contribution of High-Frequency Wind-Generated Surface Waves to the Stokes Drift

The effects of nonbreaking surface waves on upper-ocean dynamics enter the wave-averaged primitive equations through the Stokes drift. Through the resulting upper-ocean dynamics, Stokes drift is a catalyst for the fluxes of heat and trace gases between the atmosphere and ocean. However, estimates of the Stokes drift rely crucially on properly resolving the wave spectrum. In this paper, using state-of-the-art spatial measurements (in situ and airborne remote sensing) from a number of different field campaigns, with environmental conditions ranging from 2 to 13 m s−1 wind speed and significant wave height of up to 4 m, we characterize the properties of the surface wave field across the equilibrium and saturation ranges and provide a simple parameterization of the transition between the two regimes that can easily be implemented in numerical wave models. We quantify the error associated with instrument measurement limitations, or incomplete numerical parameterizations, and propose forms for the continuation of these spectra to properly estimate the Stokes drift. Depending on the instrument and the sea state, predictions of surface Stokes drift may be underestimated by more than 50%.

Kuramoto-Like Synchronization Mediated through Faraday Surface Waves

A new class of problems in free surface hydrodynamics appeared after the groundbreaking discovery by Yves Couder and Emmanuel Fort. A bouncing droplet in association with Faraday surface waves gives rise to new nonlinear dynamics, in analogy with the pilot-wave proposed by de Broglie. The droplet and the underlying vibrating bath are of silicon oil. A weakly viscous potential theory model should be used. Numerical simulations are presented with one and two bouncing droplets oscillating while confined to their cavities. These oscillators are implicitly coupled by the underlying surface wave field. In certain regimes, the oscillators can spontaneously synchronize, even when placed at a distance. Cavity parameters are varied in order to highlight the sensitive wave-mediated coupling. The present nonlinear wave-mediated oscillator synchronization is more general than that displayed by the celebrated Kuramoto model and therefore of general interest.

Surface and interfacial waves in a strongly stratified upper ocean

In an idealized two-layer fluid, surface waves can generate waves at the internal interface through class 3 resonant triads in which all waves are propagating in the same direction. The triads are restricted to wavenumbers above a critical value kcrit that depends on the density ratio R between the two layers, and their depths. We perform numerical simulations to analyze the evolution of a surface wave field, initially specified by a Pierson-Moskowitz type spectrum, for R = 0:97 (representing a realistic lower a bound for oceanic stratification). At high initial steepness and peak wavenumber kp ≪ kcrit, the energy increases in the spectral tail; as a parameterization of resulting wave breaking, at each time step individual waves with a steepness greater than the limiting Stokes steepness are removed. The energy change of the surface wave field is a combination of energy transfer to the interfacial waves, spectral downshift, and wave breaking dissipation. At wavenumbers ≳ 0:6kp there is a net loss of energy, with the greatest dissipation at ≈ 1:3kp. The maximum gain occurs at ≈ 0:5kp. The onset of the spectral change shows a strong threshold behaviour with respect to the the initial wave steepness. For steep initial waves the integrated energy dissipation can reach > 30% of the initial energy, and only ≈ 1% of the initial surface wave energy is transferred to the interfacial wave field. The spectral change could be expressed as an additional dissipation source term, and coupled ocean/wave models should include additional mixing associated with the interfacial waves and enhanced wave breaking turbulence.