scholarly journals ANALYSIS OF. TIDAL RECORDS OF THE 1964 ALASKAN TSUNAMI

1982 ◽  
Vol 1 (18) ◽  
pp. 48
Author(s):  
Basil W. Wilson
Keyword(s):  
San Francisco ◽  
Wave Train ◽  
Frequency Resolution ◽  
Energy Spectra ◽  
Spectral Energy ◽  
Secondary Wave ◽  
Primary Wave ◽  
Statistical Confidence ◽  
Computer Plot ◽  
Wave Forms

The 8. 5 magnitude Alaskan earthquake of March 27, 1964,generated a great tsunami in the Pacific Ocean. This paper presents results of energy spectrum analyses conducted on a sampling of 24 of the marigrams from some 105 tide-stations which recorded the waves. In the numerical digital procedure used, two important properties of the evolving energy spectra are invoked; the frequency resolution and statistical confidence. High confidence is obtainable only at the expense of poor resolution, and vice versa. Excessive resolution may give rise to physically unreal spectral peaks, just as excessive restrictions for confidence may cause blunting of the spectrum and possible loss of physically real spectral components. A trial-anderror compromise between these properties was sought by testing the effects on the energy spectra, for Hilo, Hawaii, of the parameters that control the digital process. An optimum selection of spectrum parameters was finally made so that the primary and secondary wave forms of components, identified by the analysis for the marigram of San Francisco, Calif., most closely agree with the corresponding wave forms obtained by use of Chrystal's (1904) graphical method of residvation analysis. Using the parameters so determined, and by application of band-pass filters in the digital analysis, the most prominent peaks of spectral energy in the marigrams of the 24 stations are isolated and their wave-forms computer-plot - ed. In all cases a recognizable long-period wave component is found having a frequency between 0.50 and 0.65 cy/hr (average period 1.73 hrs). General similarity of these primary wave forms as to period and shape of beats suggests their common origin at the source of the earthquake disturbance. The secondary wave forms of higher frequency (periods generally less than 40 mins) are ascribed to local free oscillations forced by the primary wave trains at the receiving stations. In some, but not all of the marigrams there is evidence of wave systems averaging 3.2 hrs in period. These are thought to be an independent wave-train originating at source.

Wave mechanics of breakdown

1972 ◽  
Vol 56 (4) ◽  
pp. 775-802 ◽  
Author(s):  
M. T. Landahl
Keyword(s):  
Large Scale ◽  
Wave Train ◽  
Boundary Layer Transition ◽  
Wave Crest ◽  
Secondary Wave ◽  
Small Scale ◽  
Instability Wave ◽  
Primary Wave ◽  
Wave Mechanics ◽  
Layer Transition

Kinematic wave theory is used to determine under what conditions breakdown of a steady or unsteady laminar flow into high frequency oscillations should occur. The analysis of a small-scale secondary wave riding on a large-scale inhomogeneity, such as that produced by a finite amplitude primary instability wave, reveals that the breakdown mechanism has three basic ingredients: (i) a self-excited secondary wave with a group velocity near the propagation velocity (phase velocity) of the primary wave, (ii) space-time focusing of the secondary wave train on the primary wave crest and (iii) a nonlinear filtering mechanism leading to rectification of the secondary wave.The theory is applied to a laminar shear flow. Good quantitative agreement with the experiments on boundary-layer transition by Klebanoff, Tidstrom & Sargent (1962) is found for the critical condition leading to breakdown. Also, the theory is able to explain all the main qualitative breakdown features observed by Klebanoff et al. and others, such as the rapid localized onset, and the formation of a hairpin vortex lifting up from the surface downstream of the primary wave crest.

scholarly journals Applications of a Moist Nonhydrostatic Formulation of the Spectral Energy Budget to Baroclinic Waves. Part I: The Lower-Stratospheric Energy Spectra

2015 ◽  
Vol 72 (5) ◽  
pp. 2090-2108 ◽  
Author(s):  
Jun Peng ◽  
Lifeng Zhang ◽  
Jiping Guan
Keyword(s):  
Kinetic Energy ◽  
Potential Energy ◽  
Energy Budget ◽  
Vertical Flux ◽  
Energy Spectra ◽  
Spectral Energy ◽  
Positive Contribution ◽  
Flux Divergence ◽  
Available Potential Energy ◽  
Baroclinic Waves

Abstract The authors investigate the mesoscale dynamics that produce the lower-stratospheric energy spectra in idealized moist baroclinic waves, using the moist nonhydrostatic formulation of spectral energy budget of kinetic energy and available potential energy by J. Peng et al. The inclusion of moist processes energizes the lower-stratospheric mesoscale, helping to close the gap between observed and simulated energy spectra. In dry baroclinic waves, the lower-stratospheric mesoscale is mainly forced by weak downscale cascades of both horizontal kinetic energy (HKE) and available potential energy (APE) and by a weak conversion of APE to HKE. At wavelengths less than 1000 km, the pressure vertical flux divergence also has a significant positive contribution to the HKE; however, this positive contribution is largely counteracted by the negative HKE vertical flux divergence. In moist baroclinic waves, the lower-stratospheric mesoscale HKE is mainly generated by the pressure and HKE vertical flux divergences. This additional HKE is partly converted to APE and partly removed by diffusion. Another negative contribution to the mesoscale HKE is from the forcing of a visible upscale HKE cascade. Besides the conversion of HKE, however, the three-dimensional divergence also has a significant positive contribution to the mesoscale APE. With these two direct APE sources, the lower-stratospheric mesoscale also undergoes a much stronger upscale APE cascade. These results suggest that both downscale and upscale cascades through the mesoscale are permitted in the real atmosphere and the direct forcing of the mesoscale is available to feed the upscale energy cascade.

On the Generation of Spatially Periodic Breather in a Wave Tank

2013 ◽  
Author(s):  
Takuji Waseda ◽  
Hidetaka Houtani ◽  
Katsuji Tanizawa
Keyword(s):  
Wave Train ◽  
A Priori ◽  
High Order ◽  
Unstable Wave ◽  
Wave Basin ◽  
Wave Forms ◽  
Spatially Periodic ◽  
Periodic Time Series ◽  
Wave Maker ◽  
Test Result

Spatially periodic modulational wave train was generated at the National Maritime Research Institute, Actual Sea Model Basin. The 76 m by 36 m basin of depth 4.5 m is surrounded by 382 paddle type wave generators with wave absorbing capacity. Taking advantage of this unique wave basin, we have compared two generation methods, first controlling the wave makers at both upwind and downwind sides and second controlling just the upwind side. The wave generator signal was computed a-priori by High-Order Spectral Method (HOSM hereafter). The HOSM provided temporally non-periodic time series of the unstable wave train as the wave-maker control signal. A number of wave wires located in the tank were used to compare the wave forms between two different generation methods. Our test result indicates that it is not necessary to provide signal at both ends, because the spatial evolution of the wave train remains periodic in space if the wave maker signal is appropriately controlled. The physical experiment and HOSM simulation seem to agree better with high order of nonlinearity.

scholarly journals NONLINEAR INTERACTION BETWEEN DIURNAL TIDAL AND 2-DAY WAVE IN THE METEOR WINDS OBSERVED AT CACHOEIRA PAULISTA-SP AND SÃO JOÃO DO CARIRI-PB, BRAZIL: A CASE STUDY

2013 ◽  
Vol 31 (3) ◽  
pp. 403 ◽  
Author(s):  
Edvaldo De Oliveira Alves ◽  
Lourivaldo Mota Lima ◽  
Amauri Fragoso De Medeiros ◽  
Ricardo Arlen Buriti ◽  
Paulo Prado Batista ◽  
...  
Keyword(s):  
Spectral Energy ◽  
Secondary Wave ◽  
Nonlinear Coupling ◽  
Meteor Radar ◽  
Bispectral Analysis ◽  
Atmospheric Tide ◽  
Linear Coupling ◽  
Atmospheric Wave ◽  
June July

ABSTRACT. Simultaneous measurements of meteor winds obtained in S˜ao Jo˜ao do Cariri-PB and Cachoeira Paulista-SP, Brazil, during June-July 2008 were used to investigate the occurrence of nonlinear coupling between atmospheric wave modes. The wind spectrum showed the quasi simultaneous presence of spectral energy peaks in the periods near 16, 24 and 48 hours, consistent with the occurrence of interaction between 48-h and 24-h waves, and the generation of 16-h waves. From the bispectral analysis, it was possible to confirm the occurrence of a 16-hour secondary wave generated by non-linear coupling between the 2-day and diurnal tide primary waves.Keywords: atmospheric tide, bispectral analysis, meteor radar. RESUMO. Medidas simultâneas de ventos meteóricos obtidos em São João do Cariri-PB e Cachoeira Paulista-SP, Brasil, durante os meses de junho e julho de 2008, foram usadas para investigar a ocorrência de acoplamento não linear entre modos de ondas atmosféricas. Os espectros dos ventos evidenciaram a presença quase simultânea de picos de energia espectral nos períodos de ∼ 16, ∼ 24 e ∼ 48 horas, compatíveis com a ocorrência de interação entre as ondas de 48 e 24 horas, e a geraçao da onda de 16 horas. Através de análise biespectral foi possível confirmar que a onda secundária de 16 horas foi gerada pelo acoplamento não linear entre as ondas primárias de 2 dias e a maré diurna.Palavras-chave: maré atmosférica, análise biespectral, radar meteórico.

scholarly journals Correlation Analysis between Wave Parameters using Wave Data Observed in HeMOSU-1&2

2021 ◽  
Vol 33 (4) ◽  
pp. 139-147
Author(s):  
Uk-Jae Lee ◽  
Dong-Hui Ko ◽  
Hong-Yeon Cho ◽  
Nam-Sun Oh
Keyword(s):  
Correlation Analysis ◽  
Wave Height ◽  
Wave Train ◽  
Wave Spectrum ◽  
Correlation Coefficients ◽  
Spectral Energy ◽  
Analysis Method ◽  
Peak Period ◽  
Wave Parameters ◽  
Elevation Data

In this study, waves were defined using the water surface elevation data observed from the HeMOSU-1 and 2 marine meteorological observation towers installed on the west coast of Korea, and correlation analysis was performed between wave parameters. The wave height and wave period were determined using the wave-train analysis method and the wave spectrum analysis method, and the relationship between the wave parameters was calculated and compared with the previous study. In the relation between representative wave heights, most of the correlation coefficients between waves showed a difference of less than 0.1% in error rate compared to the previous study, and the maximum wave height showed a difference of up to 29%. In addition, as a result of the correlation analysis between the wave periods, the peak period was estimated to be abnormally large at rates of 2.5% and 1.3% in HeMOSU-1&2, respectively, due to the effect of the bimodal spectrum that occurs when the spectral energy density is small.

scholarly journals Electromagnetic Propagation in an Almost Homogeneous Medium

1958 ◽  
Vol 11 (1) ◽  
pp. 118 ◽  
Author(s):  
VW Bolie
Keyword(s):  
Exact Solution ◽  
Refractive Index ◽  
Homogeneous Medium ◽  
Secondary Wave ◽  
Primary Wave ◽  
Electromagnetic Propagation ◽  
Axis Of Symmetry

This paper concerns the development from Maxwell's electromagnetic equations of an equation of propagation in an almost homogeneous medium. The equation is applied to the problem of determining the secondary wave produced by an isolated Gaussian-shaped perturbation in the refractive index. An exact solution is obtained for points located on the axis of symmetry parallel to the direction of propagation of the incident primary wave.

The instability of internal gravity waves to localised disturbances

1995 ◽  
Vol 13 (2) ◽  
pp. 196-210 ◽  
Author(s):  
J. Vanneste
Keyword(s):  
Gravity Waves ◽  
Middle Atmosphere ◽  
Internal Gravity Wave ◽  
Wave Interaction ◽  
Internal Gravity Waves ◽  
Secondary Wave ◽  
Primary Wave ◽  
Interaction Domain ◽  
Linear Correction ◽  
Basic Equations

Abstract. The instability of an internal gravity wave due to nonlinear wave-wave interaction is studied theoretically and numerically. Three different aspects of this phenomenon are examined. 1. The influence of dissipation on both the resonant and the nonresonant interactions is analysed using a normal mode expansion of the basic equations. In particular, the modifications induced in the interaction domain are calculated and as a result some modes are shown to be destabilised by dissipation. 2. The evolution of an initial unstable disturbance of finite vertical extent is described as the growth of two secondary wave packets travelling at the same group velocity. A quasi-linear correction to the basic primary wave is calculated, corresponding to a localised amplitude decrease due to the disturbance growth. 3. Numerical experiments are carried out to study the effect of a basic shear on wave instability. It appears that the growing secondary waves can have a frequency larger than that of the primary wave, provided that the shear is sufficient. The instability of waves with large amplitude and long period, such as tides or planetary waves, could therefore be invoked as a possible mechanism for the generation of gravity waves with shorter period in the middle atmosphere.

Nonlinear instability of a supersonic boundary layer with two-dimensional roughness

2014 ◽  
Vol 752 ◽  
pp. 497-520 ◽  
Author(s):  
Olaf Marxen ◽  
Gianluca Iaccarino ◽  
Eric S. G. Shaqfeh
Keyword(s):  
Boundary Layer ◽  
Large Amplitude ◽  
Supersonic Boundary Layer ◽  
Secondary Instability ◽  
Secondary Wave ◽  
Nonlinear Instability ◽  
Transient Growth ◽  
Primary Wave ◽  
Two Dimensional ◽  
Lower Amplitude

AbstractNonlinear instability in a supersonic boundary layer at Mach 4.8 with two-dimensional roughness is investigated by means of spatial direct numerical simulations (DNS). It was previously found that an important effect of a two-dimensional roughness is to increase significantly the amplitude of two-dimensional waves downstream of the roughness in a certain frequency band through enhanced instability and transient growth, while waves outside this band are damped. Here, we investigate the nonlinear secondary instability induced by a large-amplitude two-dimensional wave, which has received a significant boost in amplitude from this additional roughness-induced amplification. Both subharmonic and fundamental secondary excitation of the oblique secondary waves are considered. We found that even though the growth rate of the secondary perturbations increases compared to their linear amplification, only in some of the cases was a fully resonant state attained by the streamwise end of the domain. A parametric investigation of the amplitude of the primary wave, the phase difference between the primary and the secondary waves, and the spanwise wavenumber has also been performed. The transient growth experienced by the primary wave was found to not influence the secondary instability for most parameter combinations. For unfavourable phase relations between the primary and the secondary waves, the phase speed of the secondary wave decreases significantly, and this hampers its growth. Finally, we also investigated the strongly nonlinear stage, for which both the primary and the subharmonic secondary waves had a comparable, finite amplitude. In this case, the growth of the primary waves was found to vanish downstream of the transient growth region, resulting in a lower amplitude than in the absence of the large-amplitude secondary wave. This feedback also decreases the amplification rate of the secondary wave.

Sleep Stage Classification Based on EEG Signals by Using Improved Hilbert-Huang Transform

2011 ◽  
Vol 138-139 ◽  
pp. 1096-1101
Author(s):  
Xue Li Shen ◽  
Ying Le Fan
Keyword(s):  
Sleep Stage ◽  
Frequency Resolution ◽  
Optimal Decision ◽  
Spectral Energy ◽  
Sleep Stages ◽  
Sleep Staging ◽  
Intrinsic Mode Functions ◽  
Eeg Signals ◽  
Hilbert Huang Transform ◽  
Time Frequency

Research on automatic sleep staging based on EEG signals has a significant meaning for objective evaluation of sleep quality. An improved Hilbert-Huang transform method was applied to time-frequency analysis of non-stable EEG signals for the sleep staging in this paper. In order to settle the frequency overlapping problem of intrinsic mode function obtained from traditional HHT, wavelet package transform was introduced to bandwidth refinement of EEG before the empirical mode decomposition was conducted. This method improved the time-frequency resolution effectively. Then the intrinsic mode functions and their marginal spectrums would be calculated. Six common spectrum energies (or spectral energy ratios) were selected as characteristic parameters. Finally, a probabilistic nearest neighbor method for statistical pattern recognition was applied to optimal decision. The experiment data was from the Sleep-EDF database of MIT-BIH. The classification results showed that the automatic sleep staging decisions based on this method conformed roughly with the manual staging results and were better than those obtained from traditional HHT obviously. Therefore, the method in this paper could be applied to extract features of sleep stages and provided necessary dependence for automatic sleep staging.

scholarly journals Mesoscale Energy Spectra of the Mei-Yu Front System. Part II: Moist Available Potential Energy Spectra

2014 ◽  
Vol 71 (4) ◽  
pp. 1410-1424 ◽  
Author(s):  
Jun Peng ◽  
Lifeng Zhang ◽  
Yu Luo ◽  
Chunhui Xiong
Keyword(s):  
Kinetic Energy ◽  
Potential Energy ◽  
Lower Stratosphere ◽  
Vertical Flux ◽  
Energy Spectra ◽  
Spectral Energy ◽  
Positive Contribution ◽  
Spectral Slope ◽  
Upper Troposphere ◽  
Available Potential Energy

Abstract In Part II of this study, a new formulation of the spectral energy budget of moist available potential energy (MAPE) and kinetic energy is derived. Compared to previous formulations, there are three main improvements: (i) the Lorenz available potential energy is extended into a general moist atmosphere, (ii) the water vapor and hydrometeors are taken into account, and (iii) it is formulated in a nonhydrostatic framework. Using this formulation, the mesoscale MAPE spectra of the idealized mei-yu front system simulated in Part I are further analyzed. At the mature stage, the MAPE spectra in the upper troposphere and lower stratosphere also show a distinct spectral transition in the mesoscale: they develop an approximately −3 spectral slope for wavelengths longer than 400 km and − spectral slope for shorter wavelengths. In the upper troposphere, mesoscale MAPE is mainly deposited through latent heating and subsequently converted to other forms of energy at the same wavenumber. At wavelengths longer than roughly 400 km, the conversion of MAPE to horizontal kinetic energy (HKE) dominates, while at shorter wavelengths, the mechanical work produced by convective systems primarily adds to the potential energy of moist species and only secondarily generates HKE. However, this secondary conversion is enough to maintain the mesoscale − HKE spectral slope. Another positive contribution comes from the divergence term and the vertical flux. In the lower stratosphere, the main source of mesoscale MAPE is the conversion of HKE, although the vertical flux and the spectral transfer also have notable contributions.

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