Wave Spectral Shape Research Articles

Observational Evidence of a Saturated Gravity Wave Spectrum in the Troposphere and Lower Stratosphere

Radial velocity and temperature data obtained at the MU Radar Observatory during October and November 1986 are used to examine the character of the motion spectrum in the troposphere and lower stratosphere. It is found that the spectrum is dominated by low-frequency gravity waves with an upward sense of propagation in the lower stratosphere and both upward and downward propagation in the troposphere. Vertical wavenumber spectra of velocity and temperature are used to examine the consistency of the motion spectrum with the saturated spectrum of gravity waves proposed by Smith et al. Results indicate excellent agreement of the observed and predicted velocity and temperature spectra in both amplitude and slope. Vertical wavenumber spectra in area-preserving form reveal a dominant vertical wavelength of ∼2.5 km, systematic variations in energy density and the dominant vertical scale with time, and consistency between the temporal variations of velocity and temperature variance. Taken together, our results provide strong support both for the view that velocity and temperature fluctuations are due primarily to internal gravity waves and for the saturated spectrum theory and its imposed constraints on wave amplitudes and spectral shape.

SHALLOW-WATER SPECTRAL WAVE MODELING

A parametric shallow-water spectral wave modeling technique is developed and is tested against extensive field measurements of wave height, period and spectral shape. The wave model considers wave growth and finite water depth mechanisms such as spectral wave shoaling, wave-bottom interactions, wave-wave interactions and wave breaking. The key to this approach is that the resulting wave conditions are provided by transformation mechanisms rather than transforming spectral components during wave propagation. Thus long-term wave hindcasts can be performed economically without the loss in accuracy.

Wave climate and processes : Houmb, O.G., 1984. Ocean Sci. Engng, 9(1):1–23

The assessment of the wind wave climate is essential for all marine engineering activity including operation and design of marine structures. The design problems are related to wave characteristics and spectral shape during extreme sea states. The planning of operations require information on events of very much higher frequency than the high extremes. Thus it is necessary to have long series of wave data to account for climatic fluctuations when extremes are to be estimated. Operational criteria can be based on much shorter series of data. Instrumental wave data are so far too scarce and cover too short periods of time to describe climatic fluctuations. Therefore one has to rely on hindcasting to assess the wave climate including the high extremes. By such methods it is possible to produce information on wave height and period parameters, assuming that spectral shape is given by some analytical function.

Potential Impact of Twenty Year Hindcast Wind and Wave Climatology on Ship Design

This paper highlights some features of the Navy's new climatology which appear to extend the designer's capability to realistically assess ship performance. The climatology provides global wave and wind parameter statistics, identifies the occurrence and persistence of some heavy weather conditions, and promises to permit a substantial upgrading of wave directionality and spectral shape models. Effects of these features are summarized in terms of predicted performance of several naval combatants.

Experimental Test of the Quasilinear Theory of the Gentle Bump Instability

The nonlinear evolution of the instability resulting from a gentle bump on the tail of the electron velocity distribution of a plasma was investigated experimentally. An electron beam with a large velocity spread was injected along the axis of a collisionless plasma column immersed in a strong magnetic field. The equilibrium wave amplitude, spectral shape, and electron velocity distribution were measured and found to be in good agreement with the predictions of quasilinear theory, providing the beam met the requirements of the theory. When the beam was too strong to be a gentle bump, deviations from quasilinear theory appeared.