122 research outputs found
Wave attenuation and dispersion due to floating ice covers
Experiments investigating the attenuation and dispersion of surface waves in
a variety of ice covers are performed using a refrigerated wave flume. The ice
conditions tested in the experiments cover naturally occurring combinations of
continuous, fragmented, pancake and grease ice. Attenuation rates are shown to
be a function of ice thickness, wave frequency, and the general rigidity of the
ice cover. Dispersion changes were minor except for large wavelength increases
when continuous covers were tested. Results are verified and compared with
existing literature to show the extended range of investigation in terms of
incident wave frequency and ice conditions
Nonbreaking wave‐induced mixing in upper ocean during tropical cyclones using coupled hurricane‐ocean‐wave modeling
The effects of turbulence generated by nonbreaking waves have been investigated by testing and evaluating a new nonbreaking wave parameterization in a coupled hurricane‐ocean‐wave model. The MPI version of the Princeton Ocean Model (POM) with hurricane forcing is coupled with the WAVEWATCH‐III (WW3) surface wave model. Hurricane Ivan is chosen as the test case due to its extreme intensity and availability of field data during its passage. The model results are validated against field observations of wave heights and sea surface temperatures (SSTs) from the National Data Buoy Centre (NDBC) during Hurricane Ivan and against limited in situ current and bottom temperature data. A series of numerical experiments is set up to examine the influence of the nonbreaking wave parameterization on the mixing of upper ocean. The SST response from the modeling experiments indicates that the nonbreaking wave‐induced mixing leads to significant cooling of the SST and deepening of the mixed layer. It was found that the nondimensional constant b1 in the nonbreaking wave parameterization has different impacts on the weak and the strong sides of the storm track. A constant value of b1 leads to improved predictions on the strong side of the storm while a steepness‐dependent b1 provides a better agreement with in situ observations on the weak side. A separate simulation of the intense tropical cyclone Olwyn in north‐west Australia revealed the same trend for b1 on the strong side of the tropical cyclone
A collection of wet beam models for wave–ice interaction
Theoretical models for the prediction of decay rate and dispersion process of gravity waves traveling into an integrated ice cover expanded over a long way are introduced. The term “wet beam” is chosen to refer to these models as they are developed by incorporating water-based damping and added mass forces. Presented wet beam models differ from each other according to the rheological behavior considered for the ice cover. Two-parameter viscoelastic solid models accommodating Kelvin–Voigt (KV) and Maxwell mechanisms along with a one-parameter elastic solid model are used to describe the rheological behavior of the ice layer. Quantitative comparison between the landfast ice field data and model predictions suggests that wet beam models, adopted with both KV and Maxwell mechanisms, predict the decay rate more accurately compared to a dry beam model. Furthermore, the wet beam models, adopted with both KV and Maxwell mechanisms, are found to construct decay rates of disintegrated ice fields, though they are built for a continuous ice field. Finally, it is found that wet beam models can accurately construct decay rate curves of freshwater ice, though they cannot predict the dispersion process of waves accurately. To overcome this limitation, three-parameter solid models, termed standard linear solid (SLS) mechanisms, are suggested to be used to re-formulate the dispersion relationship of wet beam models, which were seen to construct decay rates and dispersion curves of freshwater ice with an acceptable level of accuracy. Overall, the two-parameter wet beam dispersion relationships presented in this research are observed to predict decay rates and dispersion process of waves traveling into actual ice covers, though three-parameter wet beam models were seen to reconstruct the those of freshwater ice formed in a wave flume. The wet beam models presented in this research can be implemented in spectral models on a large geophysical scale.</p
Field investigations of coastal sea surface temperature drop after typhoon passages
Sea surface temperature (SST) variability affects marine
ecosystems, fisheries, ocean primary productivity and human activities and
is the primary influence on typhoon intensity. SST drops of a few degrees in
the open ocean after typhoon passages have been widely documented; however,
few studies have focused on coastal SST variability. The purpose of this
study is to determine typhoon-induced SST drops in the near-coastal area
(within 1 km of the coast) and understand the possible mechanism. The
results of this study were based on extensive field data analysis.
Significant SST drop phenomena were observed at the Longdong Buoy in
northeastern Taiwan during 43 typhoons over the past 20 years (1998–2017).
The mean SST drop (ΔSST) after a typhoon passage was 6.1 ∘C,
and the maximum drop was 12.5 ∘C (Typhoon Fungwong in 2008). The
magnitude of the SST drop was larger than most of the observations in the open
ocean. The mean duration of the SST drop was 24 h, and on average, 26.1 h were
required for the SST to recover to the original temperature. The coastal SST
drops at Longdong were correlated with the moving tracks of typhoons. When a
typhoon passes south of Longdong, the strong and persistent longshore winds
induce coastal upwelling and pump cold water up to the surface, which is the
dominant cause of the SST drops along the coast. In this study, it was determined
that cold water mainly intruded from the Kuroshio subsurface into the Okinawa
Trough, which is approximately 50 km from the observation site. The
magnitude of coastal SST drops depends on the area of overlap between
typhoons generating strong winds and the Kuroshio. The dataset used in this
study can be accessed from https://doi.org/10.1594/PANGAEA.895002.</p
Experimental evidence for a universal threshold characterizing wave-induced sea ice break-up
Waves can drastically transform a sea ice cover by inducing break-up over
vast distances in the course of a few hours. However, relatively few detailed
studies have described this phenomenon in a quantitative manner, and the
process of sea ice break-up by waves needs to be further parameterized and
verified before it can be reliably included in forecasting models. In the
present work, we discuss sea ice break-up parameterization and demonstrate the
existence of an observational threshold separating breaking and non-breaking
cases. This threshold is based on information from two recent field campaigns,
supplemented with existing observations of sea ice break-up. The data used
cover a wide range of scales, from laboratory-grown sea ice to polar field
observations. Remarkably, we show that both field and laboratory observations
tend to converge to a single quantitative threshold at which the wave-induced
sea ice break-up takes place, which opens a promising avenue for robust
parametrization in operational forecasting models.Comment: 18 pages, 8 figures, 1 tabl
Wave modelling - the state of the art
This paper is the product of the wave modelling community and it tries to make a picture of the present situation in this branch of science, exploring the previous and the most recent results and looking ahead towards the solution of the problems we presently face. Both theory and applications are considered.
The many faces of the subject imply separate discussions. This is reflected into the single sections, seven of them, each dealing with a specific topic, the whole providing a broad and solid overview of the present state of the art. After an introduction framing the problem and the approach we followed, we deal in sequence with the following subjects: (Section) 2, generation by wind; 3, nonlinear interactions in deep water; 4, white-capping dissipation; 5, nonlinear interactions in shallow water; 6, dissipation at the sea bottom; 7, wave propagation; 8, numerics. The two final sections, 9 and 10, summarize the present situation from a general point of view and try to look at the future developments
Wind input, nonlinear interactions and wave breaking at the spectrum tail of wind-generated waves, transition from f-4 to f-5 behaviour
Behaviour of the equilibrium interval of the wave frequency spectrum is investigated. It is argued that spectra of Phillips, Toba and Zakharov-Filonenko are consistent with each other, and transition between f-4 and f-5 subintervals is parameterised by means of field data including those obtained at short fetches from Katsiveli research tower. Role of the wave breaking, wind input and nonlinear interactions in formation of the spectrum tail is discussed
Wave-coupled processes in air-sea modeling: from turbulence to climate
Abstract not available
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