scholarly journals Investigation of High-Frequency Internal Wave Interactions with an Enveloped Inertia Wave

2012 ◽  
Vol 2012 ◽  
pp. 1-12
Author(s):  
B. Casaday ◽  
J. Crockett
Keyword(s):  
Internal Wave ◽  
High Frequency ◽  
Wave Breaking ◽  
Large Scale ◽  
Critical Level ◽  
Low Frequency ◽  
Small Scale ◽  
Wave Interactions ◽  
Frequency Wave ◽  
Action Density

Using ray theory, we explore the effect an envelope function has on high-frequency, small-scale internal wave propagation through a low-frequency, large-scale inertia wave. Two principal interactions, internal waves propagating through an infinite inertia wavetrain and through an enveloped inertia wave, are investigated. For the first interaction, the total frequency of the high-frequency wave is conserved but is not for the latter. This deviance is measured and results of waves propagating in the same direction show the interaction with an inertia wave envelope results in a higher probability of reaching that Jones' critical level and a reduced probability of turning points, which is a better approximation of outcomes experienced by expected real atmospheric interactions. In addition, an increase in wave action density and wave steepness is observed, relative to an interaction with an infinite wavetrain, possibly leading to enhanced wave breaking.

Growth of low-frequency waves due to a photon beam in a magnetized electron–positron plasma

1997 ◽  
Vol 58 (2) ◽  
pp. 345-366 ◽  
Author(s):  
QINGHUAN LUO ◽  
D. B. MELROSE
Keyword(s):  
High Frequency ◽  
Random Phase ◽  
Low Frequency ◽  
Photon Beam ◽  
Radio Waves ◽  
Wave Interactions ◽  
Frequency Wave ◽  
Pair Plasma ◽  
Electron Positron ◽  
Low Frequency Waves

The effect of a beam of radio waves of very high brightness passing through a cold, magnetized, electron–positron plasma is discussed. The properties of the natural wave modes in such a plasma are summarized, and approximate forms for the nonlinear response tensor are written down. Photon-beam-induced instabilities of low-frequency waves in the pair plasma are analysed in the random-phase approximation. When three-wave interactions involve two high-frequency waves in the same mode and a low-frequency wave in a different mode, wave–wave interactions are similar to wave–particle interactions in that photons act like particles that emit and absorb low-frequency waves. The absorption coefficients for various low-frequency waves due to a photon beam are evaluated. In a pure electron–positron plasma, photon-beam-induced instabilities can be effective only when either the high-frequency or the low-frequency waves are strongly modified by the magnetic field. The growth of the low-frequency waves is most effective when the high-frequency photon beam has a frequency close to the cyclotron frequency.

Ritual Frequency, Emotionality, and Modes of Religiosity

2021 ◽  
pp. 53-81
Author(s):  
Harvey Whitehouse
Keyword(s):  
High Frequency ◽  
Large Scale ◽  
Low Frequency ◽  
New Guinea ◽  
Small Scale ◽  
Complex Societies ◽  
High Arousal ◽  
The World ◽  
Hierarchical Groups ◽  
To Come

Collective rituals tend to come in two kinds: frequently performed but relatively lowkey; rarely enacted but emotionally intense. According to the theory of modes of religiosity, high-frequency but low-arousal rituals produce large-scale hierarchical groups (the doctrinal mode), while low-frequency but high-arousal rituals produce small-scale highly cohesive groups (the imagistic mode). This chapter describes how that theory was first developed while carrying out fieldwork in the New Guinea rainforest. But then the author realized it could help to explain how groups throughout the world take shape and spread, and it could also help to explain how complex societies evolved.

Effects of Low-Frequency Wave Interactions on Intraseasonal Oscillations

2004 ◽  
Vol 61 (24) ◽  
pp. 3025-3040 ◽  
Author(s):  
Paul E. Roundy ◽  
William M. Frank
Keyword(s):  
Large Scale ◽  
Low Frequency ◽  
Austral Summer ◽  
Multiple Linear Regression Model ◽  
High Amplitude ◽  
Wave Interactions ◽  
Frequency Wave ◽  
Intraseasonal Oscillations ◽  
The Tropics

Abstract Intraseasonal oscillations (ISOs) control much of the large-scale variability of convection in the Tropics on time scales of about 15–100 days. These disturbances are often thought to be dominated by eastward-propagating modes, especially during austral summer, but disturbances that propagate westward are also important. This work demonstrates by means of a multiple linear regression model and a brief case study that eastward- and westward-moving intraseasonal modes often cooperatively interact with one another to produce many of the characteristics of the observed Southern Hemisphere summer ISO. These interactions appear to be facilitated by topography and/or by the convective anomalies that are cooperatively induced by the eastward- and the westward-moving components of the oscillations. These interactions do not occur during every period of intraseasonal convective activity, but they do commonly occur during periods of high-amplitude convective anomalies. This analysis shows that eastward- and westward-moving intraseasonal modes should not be generally assumed to be linearly independent entities.

scholarly journals Optimizing the Frequency Capping: A Robust and Reliable Methodology to Define the Number of Ads to Maximize ROAS

2021 ◽  
Vol 11 (15) ◽  
pp. 6688
Author(s):  
Jesús Romero Leguina ◽  
Ángel Cuevas Rumin ◽  
Rubén Cuevas Rumin
Keyword(s):  
High Frequency ◽  
Large Scale ◽  
Low Frequency ◽  
Digital Marketing ◽  
Optimal Frequency ◽  
Novel Technique ◽  
Maximum Threshold

The goal of digital marketing is to connect advertisers with users that are interested in their products. This means serving ads to users, and it could lead to a user receiving hundreds of impressions of the same ad. Consequently, advertisers can define a maximum threshold to the number of impressions a user can receive, referred to as Frequency Cap. However, low frequency caps mean many users are not engaging with the advertiser. By contrast, with high frequency caps, users may receive many ads leading to annoyance and wasting budget. We build a robust and reliable methodology to define the number of ads that should be delivered to different users to maximize the ROAS and reduce the possibility that users get annoyed with the ads’ brand. The methodology uses a novel technique to find the optimal frequency capping based on the number of non-clicked impressions rather than the traditional number of received impressions. This methodology is validated using simulations and large-scale datasets obtained from real ad campaigns data. To sum up, our work proves that it is feasible to address the frequency capping optimization as a business problem, and we provide a framework that can be used to configure efficient frequency capping values.

Parametric instability of internal gravity waves

1975 ◽  
Vol 67 (4) ◽  
pp. 667-687 ◽  
Author(s):  
A. D. McEwan ◽  
R. M. Robinson
Keyword(s):  
Internal Wave ◽  
Large Scale ◽  
Wave Spectrum ◽  
Parametric Instability ◽  
Mathieu Equation ◽  
Internal Gravity Waves ◽  
Small Scale ◽  
Preliminary Calculation ◽  
Theoretical Predictions ◽  
Oceanic Internal Wave

A continuously stratified fluid, when subjected to a weak periodic horizontal acceleration, is shown to be susceptible to a form of parametric instability whose time dependence is described, in its simplest form, by the Mathieu equation. Such an acceleration could be imposed by a large-scale internal wave field. The growth rates of small-scale unstable modes may readily be determined as functions of the forcing-acceleration amplitude and frequency. If any such mode has a natural frequency near to half the forcing frequency, the forcing amplitude required for instability may be limited in smallness only by internal viscous dissipation. Greater amplitudes are required when boundaries constrain the form of the modes, but for a given bounding geometry the most unstable mode and its critical forcing amplitude can be defined.An experiment designed to isolate the instability precisely confirms theoretical predictions, and evidence is given from previous experiments which suggest that its appearance can be the penultimate stage before the traumatic distortion of continuous stratifications under internal wave action.A preliminary calculation, using the Garrett & Munk (197%) oceanic internal wave spectrum, indicates that parametric instability could occur in the ocean at scales down to that of the finest observed microstructure, and may therefore have a significant role to play in its formation.

scholarly journals Internal tide energy flux over a ridge measured by a co-located ocean glider and moored ADCP

2019 ◽  
Author(s):  
Rob Hall ◽  
Barbara Berx ◽  
Gillian Damerell
Keyword(s):  
Energy Flux ◽  
Large Scale ◽  
Low Frequency ◽  
Internal Tide ◽  
Small Scale ◽  
Potential Density ◽  
The North ◽  
Model Study ◽  
Continental Shelves ◽  
Alternative Approach

Abstract. Internal tide energy flux is an important diagnostic for the study of energy pathways in the ocean, from large-scale input by the surface tide, to small-scale dissipation by turbulent mixing. Accurate calculation of energy flux requires repeated full-depth measurements of both potential density (ρ) and horizontal current velocity (u) over at least a tidal cycle and over several weeks to resolve the internal spring-neap cycle. Typically, these observations are made using full-depth oceanographic moorings that are vulnerable to being fished-out by commercial trawlers when deployed on continental shelves and slopes. Here we test an alternative approach to minimise these risks, with u measured by a low-frequency ADCP moored near the seabed and ρ measured by an autonomous ocean glider holding station by the ADCP. The method is used to measure the M2 internal tide radiating from the Wyville Thompson Ridge in the North Atlantic. The observed energy flux (4.2 ± 0.2 kW m−1) compares favourably with historic observations and a previous numerical model study. Error in the energy flux calculation due to imperfect co-location of the glider and ADCP is estimated by sub-sampling potential density in an idealised internal tide field along pseudorandomly distributed glider paths. The error is considered acceptable (

scholarly journals Abyssal plain hills and internal wave turbulence

2018 ◽  
Vol 15 (14) ◽  
pp. 4387-4403 ◽  
Author(s):  
Hans van Haren
Keyword(s):  
Internal Wave ◽  
Wave Breaking ◽  
Large Scale ◽  
Abyssal Plain ◽  
Marginal Stability ◽  
Eddy Diffusivities ◽  
North East ◽  
Mid Atlantic Ridge ◽  
Ocean Topography ◽  
Wave Induced

Abstract. A 400 m long array with 201 high-resolution NIOZ temperature sensors was deployed above a north-east equatorial Pacific hilly abyssal plain for 2.5 months. The sensors sampled at a rate of 1 Hz. The lowest sensor was at 7 m above the bottom (m a.b.). The aim was to study internal waves and turbulent overturning away from large-scale ocean topography. Topography consisted of moderately elevated hills (a few hundred metres), providing a mean bottom slope of one-third of that found at the Mid-Atlantic Ridge (on 2 km horizontal scales). In contrast with observations over large-scale topography like guyots, ridges and continental slopes, the present data showed a well-defined near-homogeneous “bottom boundary layer”. However, its thickness varied strongly with time between < 7 and 100 m a.b. with a mean around 65 m a.b. The average thickness exceeded tidal current bottom-frictional heights so that internal wave breaking dominated over bottom friction. Near-bottom fronts also varied in time (and thus space). Occasional coupling was observed between the interior internal wave breaking and the near-bottom overturning, with varying up- and down- phase propagation. In contrast with currents that were dominated by the semidiurnal tide, 200 m shear was dominant at (sub-)inertial frequencies. The shear was so large that it provided a background of marginal stability for the straining high-frequency internal wave field in the interior. Daily averaged turbulence dissipation rate estimates were between 10−10 and 10−9 m2 s−3, increasing with depth, while eddy diffusivities were of the order of 10−4 m2 s−1. This most intense “near-bottom” internal-wave-induced turbulence will affect the resuspension of sediments.

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