Wave Amplitude Research Articles

Enhancing Working Memory and Reducing Anxiety in University Students: A Neurofeedback Approach.

(1) Background: Neurofeedback training (NFT) has emerged as a promising approach for enhancing cognitive functions and reducing anxiety, yet its specific impact on university student populations requires further investigation. This study aims to examine the effects of NFT on working memory improvement and anxiety reduction within this demographic. (2) Methods: A total of forty healthy university student volunteers were randomized into two groups: an experimental group that received NFT and a control group. The NFT protocol was administered using a 14-channel Emotiv Epoc X headset (EMOTIV, Inc., San Francisco, CA 94102, USA) and BrainViz software version Brain Visualizer 1.1 (EMOTIV, Inc., San Francisco, CA 94102, USA), focusing on the alpha frequency band to target improvements in working memory and reductions in anxiety. Assessment tools, including the Corsi Block and Memory Span tests for working memory and the State-Trait Anxiety Inventory-2 (STAI-2) for anxiety, were applied pre- and post-intervention. (3) Results: The findings indicated an increase in alpha wave amplitude in the experimental group from the second day of NFT, with statistically significant differences observed on days 2 (p < 0.05) and 8 (p < 0.01). Contrary to expectations based on the previous literature, the study did not observe a concurrent positive impact on working memory. Nonetheless, a significant reduction in state anxiety levels was recorded in the experimental group (p < 0.001), corroborating NFT's potential for anxiety management. (4) Conclusions: While these results suggest some potential of the technique in enhancing neural efficiency, the variability across different days highlights the need for further investigation to fully ascertain its effectiveness. The study confirms the beneficial impact of NFT on reducing state anxiety among university students, underscoring its value in psychological and cognitive performance enhancement. Despite the lack of observed improvements in working memory, these results highlight the need for continued exploration of NFT applications across different populations and settings, emphasizing its potential utility in educational and therapeutic contexts.

Dispersion characteristics of arc-axis waveguides

Ultrasonic single mode excitation methods, mode separation algorithms and damage detection applications all require the calculation of the dispersion characteristics of the waveguide. However, existing dispersion calculation methods are mainly applicable to straight-axis waveguides. Therefore, in this paper, a novel semi-analytical finite element method in cylindrical coordinates (SAFEM-CC) is established and we focus on the dispersion characteristics of arc-axis waveguides. The cross-section of the waveguide can have arbitrary complex shapes, and the correctness of this method is verified by the finite element eigenfrequency method. At the same time, this paper takes the example of an arc-axis structure with a square cross-section and investigates the convergence of SAFEM-CC under different numbers of elements, element types, and element orders. This paper also establishes a finite element simulation model to study the waveform transmission law over a wide frequency range and the wave amplitude distribution law within the cross-section of arc-axis waveguides. The dispersion characteristics of arc-axis waveguides at different radii are also investigated. Finally, the correctness of the proposed method and the dispersion characteristics of arc-axis waveguides are verified by a large number of experiments. The main conclusions are as follows: the waveform transmission laws of the guided wave in arc-axis waveguides at each frequency agree with the dispersion curve; the theoretical wavestructure gives the distribution law of the amplitude within the cross-section; when the axis is arc, the displacement of the wavestructure on the inner and outer sides does not have symmetry, and the difference between the left and right sides gradually increases as the radius decreases.

Three-dimensional GRMHD simulations of rapidly rotating stellar core collapse

ABSTRACT We present results from fully general relativistic (GR), three-dimensional (3D), neutrino-radiation magneto-hydrodynamic (MHD) simulations of stellar core collapse of a 20 M⊙ star with spectral neutrino transport. Our focus is to study the gravitational-wave (GW) signatures from the magnetorotationally (MR)-driven models. By parametrically changing the initial angular velocity and the strength of the magnetic fields in the core, we compute four models. Among our models, only those with cores having an initial magnetic field strength of 1012 G and rotation rates of 1 or 2 rad s−1 produce MHD jets. Seen from the direction perpendicular to the rotational axis, a characteristic waveform is obtained exhibiting a monotonic time increase in the wave amplitude. As previously identified, this stems from the propagating MHD outflows along the axis. We show that the GW amplitude from anisotropic neutrino emission becomes more than one order-of-magnitude bigger than that from the matter contribution, whereas seen from the rotational axis, both of the two components are in the same order-of-magnitudes. Due to the memory effect, the frequency of the neutrino GW from our full-fledged 3D-MHD models is in the range less than ∼10 Hz. Toward the future GW detection for a Galactic core-collapse supernova, if driven by the MR mechanism, the planned next-generation detector as DECIGO is urgently needed to catch the low-frequency signals.

Experimental study of internal solitary wave evolution beneath an ice keel model

Internal solitary waves (ISWs) propagating in polar seas are affected by the sea ice at upper boundary of seas and thus exhibit complex evolution characteristics. Herein, spatiotemporal changes in the wave element, flow field, and energy of ISWs beneath an ice keel model were investigated to examine the evolution of ISWs. For this purpose, laboratory experiments were conducted using dye-tracing labeling, conductivity probes, Schlieren technology, and particle image velocimetry. The results show that ice keel causes an increase in the thickness of the pycnocline and even the occurrence of breaking and internal surging of ISW. Additionally, the waveform becomes narrower or wider at different positions, and wave amplitude and speed decrease, with a maximum reduction 30%–40%. Furthermore, the ice keel strengthens the shear of the ISW-induced flow field, generating vortices and mixing. The energy of ISWs undergoes internal conversion majorly at the front slope of the ice keel, while energy dissipation occurs largely at the back slope, with dissipation rates as high as 60%.

Computational analysis of microgravity and viscous dissipation impact on periodical heat transfer of MHD fluid along porous radiative surface with thermal slip effects

The current thermal slip and Magnetohydrodynamic analysis plays prominent importance in heat insulation materials, polishing of artificial heart valves, heat exchangers, magnetic resonance imaging and nanoburning processes. The main objective of the existing article is to deliberate the impact of thermal slip, thermal radiation and viscous dissipation on magnetized cone embedded in a porous medium under reduced gravitational pressure. Convective heating characteristics are used to increase the rate of heating throughout the porous cone. For viscous flow along a heated and magnetized cone, the conclusions are drawn. The simulated nonlinear partial differential equations are transformed into a dimensionless state by means of suitable non-dimensional variables. The technique of finite differences is implemented to solve the given model with Gaussian elimination approach. The FORTRAN language is used to make uniform algorithm for asymptotic results according to the boundary conditions. The influence of controlling parameters, such as thermal radiation parameter Rd, Prandtl number Pr, porosity parameter Ω, viscous dissipation parameter Ec, δ thermal slip parameter, Rg reduced gravity parameter and mixed convection parameter λ is applied. Graphical representations were created to show the consequences of various parameters on velocity, temperature and magnetic field profiles along with fluctuating skin friction, fluctuating heat and oscillatory current density. It is found that velocity and temperature profile enhances as radiation parameter enhances. It is noted that the amplitude and oscillations in heat transfer and electromagnetic waves enhances as magnetic Prandtl factor increases.

Gravitational waves and tadpole resummation: Efficient and easy convergence of finite temperature QFT

We demonstrate analytically and numerically that “optimized partial dressing” (OPD) thermal mass resummation, which uses gap equation solutions inserted into the tadpole, efficiently tames finite-temperature perturbation theory calculations of the effective thermal potential, without necessitating use of the high-temperature approximation. An analytical estimate of the scale dependence for OPD resummation, standard Parwani resummation (Daisy resummation), and dimensional reduction shows that OPD has similar scale dependence to dimensional reduction, greatly improving Parwani resummation. We also elucidate how to construct and solve the gap equation for realistic numerical calculations, and demonstrate OPD’s improved accuracy for a toy scalar model. OPD’s improved accuracy is most physically significant when the high-temperature approximation breaks down, rendering dimensional reduction unusable and Parwani resummation highly inaccurate, with the latter underestimating the maximal gravitational wave amplitude for the model by 2 orders of magnitude compared to OPD. Our work highlights the need to bring theoretical uncertainties under control even when analyzing broad features of a model. Given the simplicity of the OPD compared to two-loop dimensional reduction, as well as the ease with which this scheme handles departures from the high-temperature expansion, we argue this scheme has great potential in analyzing the parameter space of realistic beyond the Standard Model models. Published by the American Physical Society 2024

Continuous casting process based on an optimized submerged entry nozzle

Continuous casting process is an important part in the steel manufacturing process. The slab production quality is commonly influenced by mould and flow pattern of submerged entry nozzles (SEN). Hence, the present work aimed to attain a more liquid flow rate to increase the slab production quantity within a certain period. Moreover, a novel African Buffalo Algorithm (ABA) is presented in this work to optimise the SEN parameters and the SEN was designed in the MATLAB environment. The developed ABA model optimises the design parameters of SEN such as the size of the nozzle, the shape of the port, length, submergence depth, etc. The fitness of buffalo effectively optimises the SEN parameters and by utilising the optimised design parameters, the SEN was resigned in the MATLAB to identify the proposed framework's effectiveness. The results demonstrated that the liquid flow rate is increased and surface tension gets minimised. When the flow rate of liquid grows, the wave amplitude also upturns. The effect of liquid and air flow rate, port shape and size, maximum wave amplitude, surface tension, etc., were calculated with 0° parallel port. In addition, the presented SEN's results were compared with other existing SEN to determine the optimised SEN's effectiveness. The comparison result demonstrated that the designed optimised SEN has a high liquid flow rate, casting speed, density and viscosity.

Steady-state triad resonance between a surface gravity wave and two hydroacoustic waves based on the homotopy analysis method

Under water compressibility, resonant triads can occur within the family of acoustic-gravity waves. This work investigates steady-state triad resonance between a surface gravity wave and two hydroacoustic waves. The water-wave equations are solved as a nonlinear boundary value problem using the homotopy analysis method (HAM). Within the HAM framework, a potential singularity resulting from exact triad resonance is avoided by appropriately choosing the auxiliary linear operator. The resonant hydroacoustic wave component, along with the two primary waves (one hydroacoustic wave and one gravity wave), is considered to determine an initial guess for the velocity potential. Additionally, by selecting an optimal “convergence-control parameter,” the steady-state resonance between a surface gravity wave and two hydroacoustic waves is successfully obtained. It is found that steady-state resonant acoustic-gravity waves are ubiquitous under certain circumstances. The two primary wave components and the resonant hydroacoustic wave component take up most of the energy in the steady-state resonant acoustic-gravity wave system. The amplitude of the resonant hydroacoustic wave component is mainly determined by the primary hydroacoustic wave component, and the amplitudes of both hydroacoustic waves are approximately equal in all cases considered. In addition, when the overall amplitude of the wave system increases, both dimensionless angular frequencies decrease, indicating that the nonlinearity of the entire wave system becomes stronger with an increase in the wave system amplitude. The amplitude of the primary hydroacoustic wave has a relatively large effect on the system's nonlinearity. This work will enrich and deepen our understanding of acoustic-gravity waves.

The Representation of Convectively Coupled Kelvin Waves in Simulations With Modified Wave Amplitudes

AbstractConvectively coupled Kelvin waves (CCKWs) are important drivers of tropical weather and may influence extreme rainfall and tropical cyclone formation. However, directly attributing these impacts to CCKWs remains a challenge. Numerical models also struggle to simulate the convective coupling of CCKWs. To address these gaps in understanding, this study examines a set of global simulations in which CCKW amplitudes are modified in the initial conditions. The Model for Prediction Across Scales –Atmosphere is used to simulate a time period in which several CCKWs coexisted around the globe, including an unusually strong CCKW located over the Atlantic. Prior to running the simulation, Kelvin‐filtered fields are identified in initial conditions and used to either amplify or dampen the initial wave amplitude. This method is effective at robustly changing the strength and structure of simulated CCKWs and can illuminate their convective coupling. Rainfall intensity within simulated CCKWs is shown to be partially controlled by column saturation fraction and deep convective inhibition. Despite the accurate depiction of most CCKWs during this time period, however, these experiments fail to simulate convective coupling in the strong Atlantic CCKW. This is true even after amplifying this wave at initialization. The cause of this failure is unclear and motivates additional work into the modeling and predictability of CCKW events. Overall, this study demonstrates that modifying CCKW amplitudes can serve as a useful tool for understanding CCKWs. This method may also be useful for future attributional work on the influence of CCKWs on other phenomena.

Evaluation of vasovagal tonus index and electrocardiographic parameters in horses using a new modified base apex lead method.

Vasovagal tonus index (VVTI) serves as a straightforward assessment tool for autonomic function during both physiological and pathological conditions, including pregnancy, in horses. Obtaining VVTI through a modified base apex lead system could be a practical and comfortable solution. In this study, we assessed VVTI in horses with respect to training status and electrocardiographic measurements utilizing a novel modified base apex lead technique. A total of 12 Thai native crossbred horses and 12 Arabian horses, all free of cardiac abnormalities, were enrolled in the study. Animals underwent electrocardiogram (ECG) and VVTI using both the base-apex lead method and its modified version. 25 mm/s and 10 mm/mV ECG recordings provided standard bipolar limb leads. The amplitudes and durations of P waves, QRS complexes, PR interval, QT interval, and T duration were assessed. The T wave's shape was examined. Each recording's R-R interval was utilized to assess heart rate. Twenty consecutive beats were used to compute the variability of heart rate (VVTI). The P wave amplitude was the only significant difference (p < 0.05) between the base apex lead method and the modified base apex lead method, with no variations in heart rate, P duration, PR interval, T duration, and QRS duration and amplitude. Both methods showed mainly biphasic T wave patterns. The VVTI values of all horses did not differ significantly between the base apex and modified base apex methods. There was no significant difference in VVTI between Thai crossbred horses and Arabian horses in either method. This study provided the first evidence that VVTI can be evaluated using the modified base apex lead system and may be useful for cardiovascular function monitoring in horses.

Comparing Gravity Waves in a Kilometer‐Scale Run of the IFS to AIRS Satellite Observations and ERA5

AbstractAtmospheric gravity waves (GWs) impact the circulation and variability of the atmosphere. Sub‐grid scale GWs, which are too small to be resolved, are parameterized in weather and climate models. However, some models are now available at resolutions at which these waves become resolved and it is important to test whether these models do this correctly. In this study, a GW resolving run of the European Center for Medium‐Range Weather Forecasts (ECMWF) Integrated Forecasting System (IFS), run with a 1.4 km average grid spacing (TCo7999 resolution), is compared to observations from the Atmospheric Infrared Sounder (AIRS) instrument, on NASA's Aqua satellite, to test how well the model resolves GWs that AIRS can observe. In this analysis, nighttime data are used from the first 10 days of November 2018 over part of Asia and surrounding regions. The IFS run is resampled with AIRS's observational filter using two different methods for comparison. The ECMWF ERA5 reanalysis is also resampled as AIRS, to allow for comparison of how the high resolution IFS run resolves GWs compared to a lower resolution model that uses GW drag parametrizations. Wave properties are found in AIRS and the resampled models using a multi‐dimensional S‐Transform method. Orographic GWs can be seen in similar locations at similar times in all three data sets. However, wave amplitudes and momentum fluxes in the resampled IFS run are found to be significantly lower than in the observations. This could be a result of horizontal and vertical wavelengths in the IFS run being underestimated.

The Influence of Topography on the Diurnal Rainfall Propagation in the Bay of Bengal

Abstract A significant diurnal offshore propagation of rainfall is observed extending from the eastern coast of India to the central Bay of Bengal. This study focuses on understanding the influence of topography over the Indian subcontinent on this rainfall propagation through a series of semi-idealized mesoscale numerical simulations. These simulations with varying topography highlight the crucial role of inertia–gravity waves, driven by diurnal mountain–land–sea thermal contrast between India and the Bay of Bengal, in initiating and promoting the offshore propagation of convective systems in the Bay. These waves’ phase speed of around 14.8 m s−1 aligns well with the speed of diurnal rainfall propagation. Even after eliminating the impact of Indian topography, the offshore propagating signal persists, suggesting a secondary rather than dominant effect of terrain on offshore rainfall propagation. Furthermore, the topography affects the depth of diurnal heating within the land’s boundary layer, which thus influences the amplitude, phase, and speed of the inertia–gravity waves. Specifically, the presence of higher mountains along the coastal area drives faster waves by increasing heating depth, resulting in faster rainfall propagation. Significance Statement This study advances our comprehension of the fundamental driver behind diurnal offshore rainfall propagation and the manner in which coastal terrain influences the rainfall pattern. We demonstrate that the diurnal offshore propagation of rainfall is closely related to inertia–gravity waves generated by thermal contrasts, and we successfully distinguish these waves in our study. Furthermore, our findings indicate that elevated coastal topography contributes to a greater heating depth near the coastline, which plays a crucial role in driving faster gravity waves and, consequently, leading to faster rainfall propagation. These outcomes provide a deeper insight into the mechanism governing offshore rainfall propagation and underscore the impact of real-world topography.

Defect detection and imaging using electromagnetic acoustic transducer with butterfly coil.

Electromagnetic ultrasonic detection technology utilizes the electromagnetic coupling method to generate and receive ultrasonic waves without a couplant, which is suitable for rapid detection. However, the detection can be affected by the spatial distribution of the acoustic field and the polarization direction of the shear wave, which can result in suboptimal detection performance. The acoustic field directivity of the shear wave generated by the butterfly coil electromagnetic acoustic transducer was measured using the transmission method. The data indicate that the acoustic pressure amplitude of the shear wave is maximized along the axis of the acoustic field, thereby meeting the requirements of synthetic aperture focusing technique imaging. We used the reflection method to detect the through-hole defects and investigated the effect of shear wave polarization direction. By comparing the experimental data and imaging results, it can be concluded that higher echo amplitudes are obtained when the polarization direction of the shear wave is perpendicular to the axis of the through-hole defects. Based on the explosive reflection model, the frequency domain phase shift migration (PSM) method converts the time-domain signal to the frequency domain for processing and uses a phase-shift factor for layer-by-layer imaging. We used the PSM method to process the experimental data, which not only produced high-resolution images but also had a high computational speed.

Non-Destructive Inspection Method Using Elastic Waves for Quality Management in the Bending Process Region of BFRTP

In order to establish a sustainable infrastructure, structures must maintain their minimum required performance for an extended period. Typically, existing concrete structures are reinforced with steel, but the susceptibility of steel reinforcements to corrosion, attributed to factors such as carbonation and chlorides, can lead to performance degradation, rendering the specified requirements unmet. As a remedy, there has been a growing interest in using lightweight and corrosion-resistant fiber-reinforced polymer (FRP) bars as an alternative to traditional steel reinforcement in concrete structures. Particularly noteworthy is the use of FRP bars manufactured with thermoplastic resins (FRTP) due to their ease of processing and convenient applicability on construction sites. This study delves into the mechanical behavior evaluation by examining the propagation characteristics of elastic waves in the curved section of basalt FRTP (BFRTP). Multiple BFRTP bars underwent a 180-degree bending process, subject to various conditions, including heat and twist variations. Subsequent measurements focused on the propagation characteristics of elastic waves in the curved sections, emphasizing wave attenuation, frequency features, and propagation velocity. Additionally, bending tensile tests were conducted on the curved bars, and a comparative analysis was performed between the tensile strength and the aforementioned elastic wave propagation characteristics. The results affirm a consistent correlation between the propagation characteristics of elastic waves (amplitude ratio, centroid frequency, velocity) during the traversal of the curved BFRTP section and its tensile strength. Notably, both centroid frequency and velocity exhibited correlation coefficients exceeding 0.7, suggesting their potential efficacy as reliable indicators for estimating tensile strength.

Research on Optimization of Water Jet Coupling System Parameters in Automated Ultrasonic Phased Array Inspection

When ultrasonic testing is used for non-destructive testing of welded workpieces, the surface of the ultrasonic transducer or wedge should have a good coupling effect with the measured surface of the workpiece. However, in actual ultrasonic testing, it is difficult to ensure that the ultrasonic transducer completes uniform scanning, resulting in poor coupling between the probe and the workpiece, resulting in low acoustic coupling stability of ultrasonic testing. In view of the above problems, this paper designs and constructs an automated ultrasonic phased array inspection platform using water jet coupling. By taking water flow rate, coupling distance, and transducer center frequency as independent variable parameters of the water jet coupling system, and using the received sound wave amplitude as the response variable for experimental comparison, a response surface analysis is conducted on these parameters to optimize the detection resolution of the automated ultrasonic inspection system. The results show that the most accurate system detection results are achieved when the water flow rate is 0.4 L/min, the coupling distance is between 1.0-1.6 mm, and the transducer center frequency is 10 MHz. This effectively solves the problem of low stability in ultrasound detection coupling, improves the detection efficiency, and provides guidance for further research on the imaging effect of automated ultrasonic phased array inspection in subsequent studies.

Data-driven modeling of equatorial atmospheric waves: The role of moisture and nonlinearity on global-scale instabilities and propagation speeds.

The equatorial region of the Earth's atmosphere serves as both a significant locus for phenomena, including the Madden-Julian Oscillation (MJO), and a source of formidable complexity. This complexity arises from the intricate interplay between nonlinearity and thermodynamic processes, particularly those involving moisture. In this study, we employ a normal mode decomposition of atmospheric reanalysis ERA-5 datasets to investigate the influence of nonlinearity and moisture on amplitude growth, propagation speed, and mode coupling associated with equatorially trapped waves. We focus our analysis on global-scale baroclinic Kelvin and Rossby waves, recognized as crucial components contributing to the variability of the MJO. We examine the dependence of wave amplitudes on the background moisture field in the equatorial region, as measured by total column water vapor. Our analysis demonstrates the crucial role of moisture in exciting these waves. We further investigate the dependence of the propagation speed of the waves on their amplitudes and the background moisture field. Our analysis reveals a robust correlation between the phase speed of the normal modes and their corresponding amplitude, whereas a weaker correlation is found between the eigenmodes' phase speed and the moisture field. Hence, our findings suggest that moisture plays a role in exciting the global-scale Rossby-Kelvin structure of the MJO. In this context, the propagation speed of the eigenmodes is mainly influenced by their amplitudes, underscoring the significant role of nonlinearity in wave propagation.

Estimation of soil moisture of a high Andean wetland ecosystem (Bofedal) with geo-radar data and In-Situ measurements, Ayacucho - Peru

High Andean ecosystems within microbasins serve as crucial areas for water recharge, containing both surface and subsurface moisture. However, these ecosystems are currently under threat due to overgrazing, degradation, and the impacts of climate change. The objective is to validate the subsoil moisture of bofedal estimated using ground-penetrating radar (GPR) data in comparison to in-situ measurements obtained with a soil moisture meter (SMM) in the Apacheta microbasin of the Ayacucho region. The validation method involves comparing soil moisture values obtained with the SMM, with the estimated dielectric permittivity (DP) values from GPR surveys along four transects (T) in a bofedal. Reflected wave amplitude data are converted to DP values to identify water pockets (70<DP<81) and saturated soil moisture (10<DP<40). An analysis of the determination coefficient R2 and the Kappa index (κ) was conducted between both groups of bofedal subsoil moisture data along the four surveyed transects at depths ranging from 0 to 24 cm that contain water and saturated moisture. T1 contains a volume of 1,16m3 (47.85 %), T2 has 0.98m3 (46.6 %), T3 lacks water (40.8 %), and T4 holds 0.63m3 (31.45 %). The correlation of DP data with SMM for T1 (R2=0.801), T2 (R2=0.949), T3 (R2=0.837) y T4 (R2=0.842) implies that the SMM measurements significantly explain the estimated DP. Moreover, the kappa test demonstrated good agreement reliability between both observations made with GPR and SMM, with κ=0.763;[95%CI:0.471−1.055], indicating that the GPR method for measuring subsoil moisture is acceptable with an 87.5% confidence level.

Large-amplitude plasma wave generation by laser beating in inhomogeneous magnetized plasmas

Large-amplitude plasma wave is known to accelerate electrons to high energies. The electron energy gain mainly depends on plasma wave amplitude. In this paper, we investigate the excitation of large-amplitude plasma waves by laser beat-wave in an inhomogeneous plasma. The idea behind this work is to employ linear and radial plasma density profiles to enhance the plasma wave amplitude. PIC simulations are used to validate the numerical solution of the nonlinear wave equation in cylindrical dimensions through the finite difference method. Furthermore, the effects of the quadratic-radial plasma density profiles and magnetic field on the plasma wave excitation are investigated. The study shows that compared to the linear density profile of plasma, the plasma wave amplitude in the case of a linear-radial density profile is far more pronounced. For the linear-radial density profile, the plasma wave amplitude remains steady over greater distances of propagation compared to the linear density profile, resulting in reduced immediate damping effects. It can also be seen that the plasma wave amplitude is higher for the quadratic-radial than for the linear-radial density profiles. The effect of a longitudinal magnetic field on plasma wave amplitude is investigated. It can be seen that the plasma wave amplitude is increased by applying a magnetic field. This study may provide a way to enhance the plasma wave field for accelerating the electrons in laser-plasma accelerators.

Moisture Dependence of an African Easterly Wave Within the West African Monsoon System

AbstractThe growth and propagation of African easterly waves (AEWs) remains an active area of research, especially for those that become tropical cyclones (TCs). This is partly due to the complex role of moisture, realized through AEW‐convection interactions. The goal of this study is to understand how environmental moisture plays a role in influencing the growth and propagation of a case of an AEW‐convection system, that became a TC and how that role relates to the West African Monsoon System. Moisture sensitivity experiments were performed in a regional and convection‐permitting novel configuration. It is found that in a moister environment, diabatic heating associated with convection coupled to the wave is shallower, ultimately, weakening the wave amplitude. Energetics are reduced in a moister environment as the African easterly jet strengthens, yet narrows, and shifts northward limiting interaction with the monsoon and the wave‐convection system. The more intense monsoonal flow in a moister environment can instigate the decoupling between convection and AEW as deep convection is more likely in the ridge rather than in the trough region. Over western Africa, more continuous rainfall over the Guinea Highlands can inhibit phase locking with the AEW. In a moister environment, the mean zonal flow is weaker and as a result, the westward translation speed of the wave due to mean flow advection is slower than in the other experiments. While the mean flow advection dominates the translation, further differences in phase speed arise from differences in convection within the wave.

Beam‐Driven Electron Cyclotron Harmonic and Electron Acoustic Waves as Seen in Particle‐In‐Cell Simulations

AbstractRecent study has demonstrated that electron cyclotron harmonic (ECH) waves can be excited by a low energy electron beam. Such waves propagate at moderately oblique wave normal angles (∼70°). The potential effects of beam‐driven ECH waves on electron dynamics in Earth's plasma sheet is not known. Using two‐dimensional Darwin particle‐in‐cell simulations with initial electron distributions that represent typical plasma conditions in the plasma sheet, we explore the excitation and saturation of such beam‐driven ECH waves. Both ECH and electron acoustic waves are excited in the simulation and propagate at oblique wave normal angles. Compared with the electron acoustic waves, ECH waves grow much faster and have more intense saturation amplitudes. Cold, stationary electrons are first accelerated by ECH waves through cyclotron resonance and then accelerated in the parallel direction by both the ECH and electron acoustic waves through Landau resonance. Beam electrons, on the other hand, are decelerated in the parallel direction and scattered to larger pitch angles. The relaxation of the electron beam and the continuous heating of the cold electrons contribute to ECH wave saturation and suppress the excitation of electron acoustic waves. When the ratio of plasma to electron cyclotron frequency ωpe/ωce increases, the ECH wave amplitude increases while the electron acoustic wave amplitude decreases. Our work reveals the importance of ECH and electron acoustic waves in reshaping sub‐thermal electron distributions and improves our understanding on the potential effects of wave‐particle interactions in trapping ionospheric electron outflows and forming anisotropic (field‐aligned) electron distributions in the plasma sheet.