Impact of different sea surface roughness on surface gravity waves using a coupled atmosphere–wave model: a case of Hurricane Isaac (2012)

Abstract Infragravity waves on the sea surface near coastlines are occasionally excited by static displacement caused by large local earthquakes and recorded as tsunamis. However, tsunamis induced by ground motions from seismic waves are rarely observed, especially far from earthquake focal areas. We investigated seafloor pressure variations in the infragravity band at the Hikurangi subduction zone following the M 7.8 Kaikōura and M 7.1 Te Araroa earthquakes. Anomalous infragravity waves were observed at 0.2–20 mHz at sites overlying a low-velocity accretionary wedge offshore of the east coast of New Zealand’s North Island accompanying the Rayleigh-wave arrivals. The maximum amplitude of these ultra-low-frequency waves was similar to the tsunami that propagated from the earthquake focal area hours later. The amplitude of the pressure signal from these waves observed offshore varied inversely with water depth, suggesting that sea surface gravity waves were excited by Rayleigh or Love waves amplified within the accretionary wedge.

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Ensemble-Based Variational Method for Nonlinear Inversion of Surface Gravity Waves

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-19-0072.1 ◽

2020 ◽

Vol 37 (1) ◽

pp. 17-31 ◽

Cited By ~ 1

Author(s):

Wataru Fujimoto ◽

Takuji Waseda

Keyword(s):

Data Assimilation ◽

Gravity Waves ◽

Wave Model ◽

Surface Gravity ◽

Nonlinear Inversion ◽

Imaging Data ◽

Large Area ◽

Wave Groups ◽

Surface Gravity Waves ◽

Free Data

ABSTRACTFreak/rogue waves are considered to be the causes of marine accidents and their generation mechanism is closely related to the formation of wave groups. However, observations that capture the spatiotemporal evolution of coherent wave groups in directional windsea are rather limited. The paper presents a new technique known as the surface wave reconstruction by ensemble adjoint-free data assimilation (SWEAD) method that enables reconstruction of a spatiotemporal wave field covering a large area from wave records limited in observational density and spatial extent. We reconstructed spatiotemporal profiles of nonlinear surface gravity waves from virtual observational data using the adjoint-free four-dimensional variational data assimilation (a4DVar) scheme. The higher-order spectral method (HOSM) is used as a forward deep-water nonlinear wave model in a realistic sea state. The a4DVar scheme uses perturbed ensemble simulations to calculate the cost function gradient and Hessian; thus, construction of an adjoint model is not needed. A few extensions of the a4DVar scheme are proposed in this study. For efficient wave reconstruction, perturbed ensemble simulation results are reused by increasing the searching direction dimension at each iteration while assuring conformity to the perturbed model’s linearity. For regularization, Fourier coefficient magnitudes are constrained by a known power spectrum from the phase-averaged wave model. Twin experiments were conducted for a unidirectional wave with virtual wave gauge data and a multidirectional wave with virtual stereo camera imaging data. For both unidirectional and multidirectional cases, nonlinear freak wave–related wave groups were well reproduced, which is impossible using a linear model.

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Phase velocity and dispersion relations of surface gravity waves in shallow sea

Marine and Freshwater Research ◽

10.1071/mf9940993 ◽

1994 ◽

Vol 45 (6) ◽

pp. 993

Author(s):

VA Kalmykov

Keyword(s):

Phase Velocity ◽

Gravity Waves ◽

Experimental Studies ◽

Finite Depth ◽

Dispersion Relations ◽

Sea Surface ◽

Surface Gravity ◽

Linear Wave ◽

Shallow Sea ◽

Surface Gravity Waves

Phase velocity and dispersion relations of surface gravity waves on the sea have been modelled by two numerical methods and the results compared with previous experimental studies. Wave nonlinearities cause deviations from linear wave relations and these deviations are seen on the sea surface in the form of sharply crested waves. The effects are amplified if wave steepness increases or wave spectra become narrower. When the effects of finite depth of water are included in the calculations, the deviations from linearity are found to increase significantly.

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Influence of Wave State and Sea Spray on the Roughness Length: Feedback on Medicanes

Atmosphere ◽

10.3390/atmos9080301 ◽

2018 ◽

Vol 9 (8) ◽

pp. 301 ◽

Cited By ~ 13

Author(s):

Umberto Rizza ◽

Elisa Canepa ◽

Antonio Ricchi ◽

Davide Bonaldo ◽

Sandro Carniel ◽

...

Keyword(s):

Surface Roughness ◽

Single Case ◽

Wind Waves ◽

Wave Model ◽

Atmospheric Model ◽

Sea Surface ◽

Sea Spray ◽

High Wind ◽

Wave State ◽

Sea Surface Roughness

Occasionally, storms that share many features with tropical cyclones, including the presence of a quasi-circular “eye” a warm core and strong winds, are observed in the Mediterranean. Generally, they are known as Medicanes, or tropical-like cyclones (TLC). Due to the intense wind forcings and the consequent development of high wind waves, a large number of sea spray droplets—both from bubble bursting and spume tearing processes—are likely to be produced at the sea surface. In order to take into account this process, we implemented an additional Sea Spray Source Function (SSSF) in WRF-Chem, model version 3.6.1, using the GOCART (Goddard Chemistry Aerosol Radiation and Transport) aerosol sectional module. Traditionally, air-sea momentum fluxes are computed through the classical Charnock relation that does not consider the wave-state and sea spray effects on the sea surface roughness explicitly. In order to take into account these forcing, we implemented a more recent parameterization of the sea surface aerodynamic roughness within the WRF surface layer model, which may be applicable to both moderate and high wind conditions. The implemented SSSF and sea surface roughness parameterization have been tested using an operative model sequence based on COAWST (Coupled Ocean Atmosphere Wave Sediment Transport) and WRF-Chem. The third-generation wave model SWAN (Simulating Waves Nearshore), two-way coupled with the WRF atmospheric model in the COAWST framework, provided wave field parameters. Numerical simulations have been integrated with the WRF-Chem chemistry package, with the aim of calculating the sea spray generated by the waves and to include its effect in the Charnock roughness parametrization together with the sea state effect. A single case study is performed, considering the Medicane that affected south-eastern Italy on 26 September 2006. Since this Medicane is one of the most deeply analysed in literature, its investigation can easily shed some light on the feedbacks between sea spray and drag coefficients.

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