Frequency Distribution Of Waves Research Articles

Plasmasphere Control of ULF Wave Distribution at Different Geomagnetic Conditions

AbstractMagnetic storms and substorms cause global disturbances in the Earth's magnetosphere. Plasma clouds injected from the magnetotail during storm or substorm drift around the Earth and generate ultra‐low frequency (ULF) waves via various mechanisms. At the same time, the inner part of the magnetosphere called plasmasphere is filled with cold particles and its characteristics are sensitive to the geomagnetic activity level. Previous theoretical and some observational studies suggested plasmasphere and its boundary, plasmapause, are special regions for ULF waves to interact with charged particles. We present a statistical analysis of ULF waves during different geomagnetic conditions. We utilized Arase satellite magnetic field and electron density measurements from March 2017 to December 2020 to investigate spatial distribution of ULF waves and its dependence on the plasmapause location. A 1–2 RE gap between the plasmapause and a region of high transverse waves occurrence rate was found. This gap keeps during quiet geomagnetic conditions when plasmasphere expands, and we concluded that the plasmapause controls the ULF wave distribution in the magnetosphere. ULF wave occurrence rate significantly decreases at quiet time, but dayside and dawnside maxima still occur for poloidal and compressional, and toroidal waves, respectively. Thus, we can distinguish internally and externally excited waves. Average wave frequency distribution revealed field‐line resonance character of toroidal waves as frequency increases toward the Earth. Poloidal and compressional waves distributions clearly distinguish low frequency externally excited waves and high frequency storm‐time pulsations.

Simulation of the gravitational wave frequency distribution of neutron star–black hole mergers* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11988101, 11773005, U2031203, U1631236, 11703001, U1731238, U1938117, 11725313, and 11721303), the International Partnership Program of Chinese Academy of Sciences (Grant No. 114A11KYSB20160008), and the National Key R&D Program of China (Grant No. 2016YFA0400702), and the Subsidy

LIGO-Virgo has observed the gravitational waves (GWs) from the coalescence of binary black hole (BBH) and binary neutron star (BNS) during O1 and O2, and the ones from NS-BH are expected to be hunted in the operating O3 run. The population properties and mass distribution of NS-BH mergers are poorly understood now, thus researchers simulated their chirp mass () distribution by a synthetic model, in which the BHs and NSs were inferred by LIGO-Virgo (O1/O2), and obtained the values in the range of . In this paper, we further simulate the GW frequency (f GW) distribution of NS-BH mergers by the above-stated synthetic model, with a basic binary system model through the Monte Carlo method. Our results predict that the median with 90% credible intervals is Hz in the case of Schwarzschild BH when the system just before merger, and this GW frequency is expected to increase several times in the merger stage, which is lying in the frequency band of LIGO-Virgo, i.e., about 15 Hz to a few kHz. Our results provide an important reference for hunting the NS-BH mergers by the on-going O3 run of LIGO-Virgo.

The influence of various frequency chorus waves on electron dynamics in radiation belts

Non-adiabatic behaviour induced by the chorus-electron interaction is an important contributor to the radiation belt dynamics, and largely relies on wave frequency distribution. During the geomagnetic storm on August 2, 2016, upper-band, lower-band and extremely low frequency (ELF) chorus waves were simultaneously observed within one orbit period of the Van Allen Probe B. Numerical simulations are performed to investigate the electron evolution by the observed chorus with different frequencies. The results show that various frequency chorus waves have different effects on electron dynamics. For chorus in the range f≈0.3fce−0.7fce, energy diffusion is the dominant process in electron evolutions. For chorus in the range 0.1fce⩽f⩽0.25fce, the pitch angle diffusion tends to be comparable to energy diffusion for Ek>0.5 MeV. For ELF chorus below 0.1fce, the pitch angle diffusion rate is much above the energy diffusion rate, leading to potential scattering losses.

Low-frequency hiss-like whistler-mode waves generated by nonlinear three-wave interactions outside the plasmasphere

Whistler-mode waves play an important role in the inner magnetospheric particle dynamics. The direction and efficiency of energy transfer between waves and particles strongly depend on the wave frequency distribution characteristics. Recent observations have drawn attention to the low-frequency whistler-mode chorus waves below 0.1 times the equatorial gyrofrequency fce of electrons outside the plasmasphere. Here, on the basis of the analysis of the Van Allen Probes wave data, we describe a new type of low-frequency hiss-like whistler-mode wave around or below 0.1 fce. We show that two normal chorus wave bands split by the 0.5 fce gap can produce the low-frequency hiss-like whistler-mode waves through the nonlinear three-wave interaction.

Simple approximations of quasi‐linear diffusion coefficients

Quasi‐linear diffusion by cyclotron‐resonant plasma waves is likely a key ingredient of the behavior of electrons in the Earth's radiation belts. Multidimensional dynamical simulations are under development, which require the diffusion coefficients to be evaluated quickly as well as accurately. The recently developed parallel propagation approximation replaces the integration over wavenormal distribution with a closed form expression, and can be quite accurate. However, it can also perform badly, especially for electron energy ≥1 MeV. Here, the accuracy, justification, and limits of the approximation are explored, and an improved version is presented. It is based on a previously developed procedure for identifying wavenormal angles compatible with imposed cutoffs on the wave frequency distribution. Because it also requires evaluation at only a small number of points, it features computational efficiency comparable to the parallel propagation version, while preserving contributions from oblique waves and all relevant harmonic numbers. Detailed comparisons are presented using an established model of nightside chorus.

Microwave propagation in dense random media

Using simple, approximate arguments, we obtain a formula that relates the average spacing between peaks in the transmitted intensityvs. wave frequency distribution of a single configuration of a random distribution of scatterers to the diffusion constant, sample thickness, and effective absorption length. The value of the diffusion constant obtained this way is found to be within 20% of the value obtained via intensity-intensity autocorrelation function techniques.

中層大気中の慣性重力波に関する統計的研究

An analysis was made of the structure and behaviour of small-scale motions in the stratosphere and lower mesosphere with the aid of meteorological rocket observations over the period of six years from 1977 to 1982, covering the wide range of latitudes.By applying a filter to observed wind data with respect to height, wind fluctuations with characteristic vertical scales close to 10km are separated from large-scale components such as the mean field, planetary waves and tides.From the hodograph analysis it is found that at northern hemisphere stations most of horizontal wind vectors show the clockwise rotation with increasing height while they rotate anti-clockwise in the southern hemisphere. This strongly suggests that the wind fluctuations are due mainly to upward propagating inertia-gravity waves.On the basis of a simplified theory of inertia-gravity waves, the wave-frequency distribution is estimated statistically from the degree of elliptic polarization of holographs, and it is shown that the most predominant values of f/ω (f; the Coriolis parameter, ω; the intrinsic wave frequency) fall into a range of 0.2-0.4. Namely, the typical time scale of these waves is of the order of several hours in middle and high latitudes and of a day in low latitudes.Further discussions are made of the vertical profile of the wave energy density, and it is suggested, from the uniform decay of the wave amplitude with height that the wide spectra of horizontal phase velocities should be taken into account.

Air-water Annular Two-phase Flow in a Horizontal Tube : 2nd Report, Circumferential Variations of Film Thickness Parameters

Experimental investigation was made on circumferential variations of the characteristics of a liquid film formed on the inner surface of a horizontal tube of 26.0 mm I.D. in which air and water flowed concurrently. Superficial velocities of the both phases ranged 10∼50 m/s for air and 0.006∼0.40 m/s for water. The flow pattern concerned was mainly an annular flow. Annular flow is subdivided into two regions characterized by liquid slug like frothy liquid lump (AF-region) and disturbance wave (AD-region). Classification can be made by examining the shape of the cumulative wave frequency distribution, plotted on normal probability paper against the radial distance from tube inner wall. A new method is proposed for separating base film from disturbance wave, which is processed on the wave frequency distribution chart. Experimental data are presented on principal parameters of liquid film such as thickness of base film, disturbance wave-height, -frequency and -velocity. A consideration is also made on the liquid transportation in disturbance wave region.

Real-time analysis of hippocampal neural activity in the intervals between interictal spikes

Previously the electroencephalogram (EEG) was modeled as consisting of faster, smaller waves superimposed on larger, slower waves. The intent of this study is to modify the program to sample neural activity over specific intervals of time following detection of a distinct wave pattern. The use of conditional sampling is illustrated by considering wave detection following epileptic interictal spikes in the rabbit hippocampus. To create an epileptic focus, small pellets of sodium penicillin suspended in agar were placed on the rabbit hippocampus. This produced regularly recurring, spontaneous, large amplitude discharges, or interictal spikes, at the site of application. Following detection of an interictal spike, the program delayed the onset of a sample period for either 1.0 s or 6.0 s. The neural activity was then sampled for 5.1 s, and fast and slow waves were detected over the sample period. The frequency distribution of waves in four of these 5.1 s intervals was calculated. Comparison of the frequency distributions following the 1.0 s and 6.0 s delays showed no discernible differences. The data illustrate that not all types of neural activity are markedly modified by interictal spikes and suggest that hippocampal cellular populations generate similar waves 1.0 s and 6.0 s after such a spike. Moreover, this experiment illustrates adaptation of the program to sample activity over a limited period of time following detection of a specific cortical waveform.

A practical method for automatic real-time EEG sleep state analysis.

A computer system for real-time analysis of the electroencephalograph (EEG) is described. The system performs continuous analysis, with graphic, analog, and tabular outputs, and storage of selected samples on disk for off-line analysis. Implemented mostly in high-level software, it is based on a two-component model of the signal in which waves are detected by a combination zero-crossing and peak detection algorithm. Each sample is classified by a pattern recognition scheme into one of several classes on the basis of the frequency distribution of waves; the classes correspond to normal sleep-awake states. Samples are taken ten times per minute and tabulated once per minute to provide a concise quantified history which is well suited to long-term EEG studies. Alternate independent information channels allow verification of results. Samples stored on disk may be grouped and averaged for statistical comparisons of EEG signal characteristics. The state classification algorithm has been tailored to the EEG of the cat; the results of a series of 7-8 day sleep studies are presented.