Anomalous Wave Propagation Research Articles

Numerical Solutions of Time fractional Klein Gordon Equation using Crank-Nicolson Finite Difference Method

Finite difference methods are widely used numerical techniques used to solve partial differential equations observed in many fields, such as science and engineering. This research presents a study on the numerical solutions of the Klein-Gordon equation, which describes anomalous diffusion and wave propagation in quantum fields and possesses a fractional derivative in the Caputo sense. The content of the paper begins by discretizing the region of the problem while taking into account the fundamental characteristics of finite difference methods. Subsequently, the time derivative algorithm, and the other terms, are discretized using the Crank-Nicolson finite difference approach, resulting in a system of algebraic equations. Solving this algebraic equation system yields numerical solutions. The numerical results are calculated for various values of the parameters associated with the equation and fractional order derivatives , leading to the computation of error norms. Graphical findings illustrate the physical behavior of approximation solutions for a variety of fraction order values. Additionally, the stability analysis of the numerical scheme is investigated using von-Neumann stability analysis. The results of this paper will help other researchers studying in the field to apply the presented method to other problems modelling the natural phenomena.

Wave Manipulation in Intelligent Metamaterials: Recent Progress and Prospects

AbstractMetamaterials (MMs), which include phononic crystals (PCs) as a particular type, exhibit anomalous wave propagation properties through artificial design of topologies or lattice forms of unit‐cells. Recent advancements in MMs signify an ascendant research trend, providing promising design ideas and means for unprecedented wave propagation properties. The imperative for on‐demand, real‐time active control of wave propagation underscores the significance of tunable manipulation of acoustic/elastic waves, promoting the design and development of tunable MMs. Furthermore, the versatility of intelligent materials and their ongoing development and innovation contribute significantly to the emergence of diverse intelligent MMs. This comprehensive survey provides an overview of recent advancements and current research trends in the interdisciplinary field of intelligent MMs with electro‐/magneto‐mechanical couplings. The primary objective of the review is to emphasize significant progress in agile manipulation of acoustic/elastic waves in electro‐/magneto‐mechanical coupled MMs, followed by an in‐depth exploration of intelligent metasurfaces, topological MMs, non‐Hermitian parity‐time symmetric wave systems, odd elastic MMs, and spatiotemporally modulated MMs. Special emphasis is given to multi‐field coupling effects. The review concludes with a summary and outlines potential prospects, offering a timely and informative guide for future studies on actively tunable PCs and MMs in practical engineering applications.

A hybrid collocation method for the approximation of 2D time fractional diffusion-wave equation

<p>The multi-term time-fractional order diffusion-wave equation (MT-TFDWE) is an important mathematical model for processes exhibiting anomalous diffusion and wave propagation with memory effects. This article develops a robust numerical technique based on the Chebyshev collocation method (CCM) coupled with the Laplace transform (LT) to solve the time-fractional diffusion-wave equation. The CCM is utilized to discretize the spatial domain, which ensures remarkable accuracy and excellent efficiency in capturing the variations of spatial solutions. The LT is used to handle the time-fractional derivative, which converts the problem into an algebraic equation in a simple form. However, while using the LT, the main difficulty arises in calculating its inverse. In many situations, the analytical inversion of LT becomes a cumbersome job. Therefore, the numerical techniques are then used to obtain the time domain solution from the frequency domain solution. Various numerical inverse Laplace transform methods (NILTMs) have been developed by the researchers. In this work, we use the contour integration method (CIM), which is capable of handling complex inversion tasks efficiently. This hybrid technique provides a powerful tool for the numerical solution of the time-fractional diffusion-wave equation. The accuracy and efficiency of the proposed technique are validated through four test problems.</p>

Wavelength-independent Bragg-like reflection in uniaxial bi-anisotropic media

We have recently shown that a uniform birefringent medium exhibits a circular Bragg phenomenon that relies solely on resonant tuning of the medium’s parameters, rather than on a particular wavelength resonance, thus rendering its electromagnetic response arbitrarily broadband. The resonant condition, however, necessitated a chirality parameter equal to the average refractive index. Here, we demonstrate that non-axial wave propagation in an axially bi-anisotropic uniaxial medium also enacts such a response and, moreover, relaxes the severity of the tuning condition, offering a convenient platform for controlling both the location of the resonance and the corresponding bandwidth. Anomalous wave propagation at a singular point is additionally identified, in the vicinity of which a remarkably high and intrinsically broadband refractive index can be realized. Recent demonstrations of meta-media with giant and controllable chirality pave the path towards the realistic embodiment of a highly efficient optical modulator.

Nonlinear Effects of the Stratospheric Quasi‐Biennial Oscillation and ENSO on the North Atlantic Winter Atmospheric Circulation

AbstractPrevious studies have shown that both the stratospheric Quasi‐Biennial Oscillation (QBO) and the El Niño‐South Oscillation (ENSO) can influence the North Atlantic winter circulation. Here we use reanalysis and model output data to show that the QBO and ENSO interact to produce a nonlinear effect on the North Atlantic winter circulation. Specifically, during El Niño winters, the QBO teleconnection mainly takes a subtropical pathway with changes in the North Pacific–Atlantic subtropical jet (STJ); during La Niña winters, the QBO connects with the troposphere predominantly through a polar pathway, that is, stratospheric polar vortex (SPV) changes. Further, the QBO‐induced STJ changes in El Niño lead to anomalous Rossby wave propagation toward the North Atlantic, and the QBO‐induced SPV during La Niña anomaly exerts a downward effect on the North Atlantic. Hence, the various interactions between ENSO and QBO teleconnections result in nonlinear, and even synergistic, impacts on the North Atlantic circulation.

Some Features of the Ionospheric Radio Wave Characteristics Over China Observed During the Solar Eclipse of 21 June 2020

AbstractThe Harbin Engineering University, the People's Republic of China, multifrequency multiple‐path coherent radio system operates continuously and provides data for post analysis. The data collected during the solar eclipse of 21 June 2020 have been chosen for this study with the objectives to interpret the variations in the Doppler spectra, Doppler shift, and in the reflected radio wave amplitudes that are associated with the solar eclipse, establish the magnitude and find physical significance of these variations, determine the reduction in the electron density caused by the solar eclipse, and to estimate an increase in wave activity in the ionosphere. The eclipse was accompanied by Doppler spectrum diffuseness resulting from an increase in the number of rays, the temporal variations in the Doppler shift were observed to be bi‐polar, asymmetrical, and anomalously small, with extreme Doppler shift magnitudes varying from −11 to −40 mHz and from 22 to 56 mHz. The duration of processes with negative Doppler shifts varied from 50 to 80 min, and the duration of processes with positive Doppler shifts changed from 30 to 80 min. The multi‐hop propagation (from two to five hops) took place along all propagation paths, with a 360 to 560‐km one‐hop length, due to the anomalous radio wave propagation via the sporadic‐E layer present about 80% of the time on 21 June 2020. The Doppler shift exhibited 4–18‐min period quasi‐sinusoidal variations with 20–10‐mHz amplitudes.

Diverse Dynamical Response to Orographic Gravity Wave Drag Hotspots—A Zonal Mean Perspective

AbstractIn the extratropical atmosphere, Rossby waves (RWs) and internal gravity waves (GWs) propagating from the troposphere mediate a coupling with the middle atmosphere by influencing the dynamics therein. In state‐of‐the‐art chemistry‐climate models (CCMs), RW effects are well resolved while the majority of GW effects have to be parameterized. Here, we analyze orographic GW (OGW) interaction with resolved dynamics in a comprehensive CCM on daily time scales. For this, we apply a recently developed method of strong OGW drag event composites for three pronounced northern hemisphere OGW hotspots. We show that strong OGW drag events are associated with anomalous resolved wave propagation in the stratosphere. Causal links are inferred from previously published work and are supported by the anomalies in zonal circulation and wave activity tendencies. The nature of these anomalies varies depending on the hotspot region, which underlines the parameterized OGW‐resolved dynamics interaction being a two‐way process.

What induces the interdecadal shift of the dipole patterns of summer precipitation trends over the Tibetan Plateau?

AbstractPrecipitation on the Tibetan Plateau (TP) exert great impacts on the energy, water cycle, and regional ecosystem. But due to the wide differences in climate regimes and complicated topography, TP precipitation is characterized as greater spatial diversity and lower confidence of temporal tendency. Based on the precipitation datasets from in situ observations, reanalysis, and satellites, this study identifies the interdecadal shift of the summer precipitation trends in the southern and northern TP, which corresponds well with the remarkable changes of TP lakes area in recent years. The statistical results indicate that the TP summer precipitation has experienced an interdecadal transition in the late 1990s, with precipitation increasing and then decreasing in the southern TP, and decreasing and then increasing in the northern TP. Further analyses suggest that the changes in moisture budget and convection activities play an important role in the interdecadal variations of precipitation in the northern and southern TP, respectively. More specifically, the variations in the southern TP are contributed largely by the persistent weakening sensible heat source, which can depress the ascending motion and hinder the northward moisture transport in the southern TP. While in the northern TP, both observations and model sensitivity experiments indicate that the co‐effect of the cold interdecadal Pacific oscillation (IPO) and warm Atlantic multidecadal oscillation (AMO) has profound impacts on the decadal shift of the net moisture budget in the northern TP. Specifically, the AMO can impact the Lake Baikal anticyclone through the anomalous wave propagation and then decrease the moisture output in the eastern TP. While the IPO can weaken the climatological westerlies and prompt the moisture to get stuck in the northern TP. Consequently, the variations in the net moisture budget can give rise to the decadal variations in summer precipitation in the northern TP.

Wave propagation improvement in two-dimensional bond-based peridynamics model

In this study, methods to mitigate anomalous wave propagation in 2-D Bond-Based Peridynamics (PD) are presented. Similarly to what happens in classical non-local models, an irregular wave transmission phenomenon occurs at high frequencies. This feature of the dynamic performance of PD, limits its potential applications. A minimization method based on the weighted residual point collocation is introduced to substantially extend the frequency range of wave motion modeling. The optimization problem, developed through inverse analysis, is set up by comparing exact and numerical dispersion curves and minimizing the error in the frequency-wavenumber domain. A significant improvement in the wave propagation simulation using Bond-Based PD is observed.

A Review on the Effects of Radio Refractivity and Atmospheric Parameters on Signal Quality at Ultra High Frequency (UHF)

Refractivity is an important factor in predicting the performance of radio link. The structures of the refractive index of the troposphere are responsible for many complicated mechanisms such as, multipath effects, absorption, scattering of radio signals, etc. and these mechanisms can cause a lot of propagation impairment such as, loss of signal for mobile communication, the accuracy of tracking radio source (such as stars) with radio telescopes, radar system etc. Understanding the effects of the weather on radio wave propagation will help to improve the quality of radio signals, as the Weather variables are useful ingredients in the predictions of refractivity distributions and the anomalous radio wave propagation conditions of the atmosphere. This study contends that refractivity variations significantly affects received signal strength at Ultra High Frequency (UHF) and gave a brief theoretical background on Electromagnetic wave, Atmospheric effects on radio propagation anomalous propagation condition and the mathematical expression for refractive index and refractivity of the troposphere. Also, the paper review related articles in the following area; refractive index and refractivity of the troposphere, effects of weather variables and refractivity of troposphere. The analysis of the review articles summits that, refractivity reveals seasonal variations with high value in rainy season and low values in dry season. Also observed from the review articles, is that the diurnal variations are influenced by three atmospheric parameters; water vapour has the greatest effect on refractivity variations followed by temperature and pressure. Furthermore, the Refractivity is function of local meteorological parameters. Eventually, the study suggests that, the effect of Atmospheric parameters and consequently the Radio Refractivity should be compensated for when designing wireless communication links in an environment.

Hyperbolic dispersion metamaterials and metasurfaces

In recent years a wide interest has been spurred by the inverse design of artificial materials for nano-biophotonic applications. In particular, the extreme optical properties of artificial hyperbolic dispersion nanomaterials allowed to access new physical effects and mechanisms. The unbound isofrequency surfaces of hyperbolic metamaterials and metasurfaces allow to access virtually infinite photonic density of states, ultrahigh confinement of electromagnetic fields and anomalous wave propagation. Here, we report the most relevant physical properties of different hyperbolic dispersion material geometries and how they allow to control light-matter interaction at the single nanometer scale, in biological matter.

3D auxetic lattice materials for anomalous elastic wave polarization

Elastic bulk materials support longitudinal and transverse waves such that the former travels faster in most cases. Anomalous polarization is the case when a transverse wave travels faster, allowing us to engineer the wave propagation via wave steering, scattering control, and mode conversion, which has critical applications in vibration mitigation and ultrasonic imaging. However, realizable materials that exhibit anomalous polarization are rarely found in nature, and architected materials that exhibit this property have only been demonstrated in 2D. In this article, we present 3D auxetic periodic lattice materials that support anomalous wave polarization. Through finite element analysis, we show that these lattices can switch between normal and anomalous behavior via simple geometry changes. We confirm the elasticity condition and qualitatively discuss the guidelines to design lattice materials that support anomalous polarization along a specific wave propagation direction. We show the ability to control the anomalous wave propagation direction by modifying the lattice geometry. Further, we numerically demonstrate mode conservation, deceleration, and acceleration of an incident wave using a material that exhibits anomalous wave polarization. These demonstrations show the potential application of such materials in nondestructive evaluation and medical imaging.

Anomalous Wave Propagation in Topological Transition Metasurfaces

AbstractMetasurfaces become an effective route to the control of not only free‐space waves but also surface plasmon polaritons (SPPs). SPPs, propagating along the interface between a metal and a dielectric, show properties of strong enhancement of the local field. Thanks to these essential functionalities, manipulating SPPs in metasurfaces is of particular interest in current research. Here, observation of anomalous SPP propagation is presented when SPPs traverse an interface between two metasurfaces whose topologies of eigenmode equal‐frequency contours are different. By combining various complementary meta‐resonators, SPP propagation was ready to be redirected at the topological transition interface at will. The proposed integrated metasurfaces open unprecedented avenues for anomalous wave propagation and guidance, showing exceptional capabilities for designing photonic devices.

The Teleconnection of El Niño Southern Oscillation to the Stratosphere

AbstractEl Niño and La Niña events in the tropical Pacific have significant and disrupting impacts on the global atmospheric and oceanic circulation. El Niño Southern Oscillation (ENSO) impacts also extend above the troposphere, affecting the strength and variability of the stratospheric polar vortex in the high latitudes of both hemispheres, as well as the composition and circulation of the tropical stratosphere. El Niño events are associated with a warming and weakening of the polar vortex in the polar stratosphere of both hemispheres, while a cooling can be observed in the tropical lower stratosphere. These impacts are linked by a strengthened Brewer‐Dobson circulation. Anomalous upward wave propagation is observed in the extratropics of both hemispheres. For La Niña, these anomalies are often opposite. The stratosphere in turn affects surface weather and climate over large areas of the globe. Since these surface impacts are long‐lived, the changes in the stratosphere can lead to improved surface predictions on time scales of weeks to months. Over the past decade, our understanding of the mechanisms through which ENSO can drive impacts remote from the tropical Pacific has improved. This study reviews the possible mechanisms connecting ENSO to the stratosphere in the tropics and the extratropics of both hemispheres while also considering open questions, including nonlinearities in the teleconnections, the role of ENSO diversity, and the impacts of climate change and variability.

Topological Waveguiding near an Exceptional Point: Defect-Immune, Slow-Light, and Loss-Immune Propagation.

Electromagnetic waves propagating in conventional wave-guiding structures are reflected by discontinuities and decay in lossy regions. In this Letter, we drastically modify this typical guided-wave behavior by combining concepts from non-Hermitian physics and topological photonics. To this aim, we theoretically study, for the first time, the possibility of realizing an exceptional point between coupled topological modes in a non-Hermitian nonreciprocal waveguide. Our proposed system is composed of oppositely biased gyrotropic materials (e.g., biased plasmas or graphene layers) with a balanced distribution of loss and gain. To study this complex wave-guiding problem, we put forward an exact analysis based on classical Green's function theory, and we elucidate the behavior of coupled topological modes and the nature of their non-Hermitian degeneracies. We find that, by operating near an exceptional point, we can realize anomalous topological wave propagation with, at the same time, low group velocity, inherent immunity to backscattering at discontinuities, and immunity to losses. These theoretical findings may open exciting research directions and stimulate further investigations of non-Hermitian topological waveguides to realize robust wave propagation in practical scenarios.

Multi-dimensional [formula omitted]-fractional diffusion–wave equation and some properties of its fundamental solution

In this paper, a multi-dimensional α-fractional diffusion–wave equation is introduced and the properties of its fundamental solution are studied. This equation can be deduced from the basic continuous time random walk equations and contains the Caputo time-fractional derivative of the order α/2 and the Riesz space-fractional derivative of the order α so that the ratio of the derivatives orders is equal to one half as in the case of the conventional diffusion equation. It turns out that the α-fractional diffusion–wave equation inherits some properties of both the conventional diffusion equation and of the wave equation. In particular, in the one- and two-dimensional cases, the fundamental solution to the α-fractional diffusion–wave equation can be interpreted as a probability density function and the entropy production rate of the stochastic process governed by this equation is exactly the same as the case of the conventional diffusion equation. On the other hand, in the three-dimensional case this equation describes a kind of anomalous wave propagation with a time-dependent propagation phase velocity.

Resonances in graphene-dielectric stacks

BackgroundThis paper presents a comprehensive theoretical investigation of the anomalous electromagnetic wave propagation and resonances around the trapped modes embedded in graphene dielectric stacks.ResultsExpressions for the dispersion relation, the condition of the trapped mode, the transmission coefficient, and the instantaneous field components through the graphene stack are derived. Evanescent mode coupling to the graphene-dielectric stack arises at the discrete frequencies of the trapped modes. When the wavevector is perturbed, resonances occur around the trapped modes which results in transmission anomalies and dramatic field amplification in graphene stacks.ConclusionsAnomalous electromagnetic wave propagation and resonances in graphene-dielectric stacks are reconnoitered. The number of the conceivable discrete trapped modes and consequently the resonances in graphene-dielectric stacks can be adjusted by the graphene chemical potential.

Multi-directional adjacent wave subtraction and shifted time point mapping algorithms and their application to defect visualization in a space tank liner

We propose the multi-directional adjacent wave subtraction (MAWS), shifted time point (STP) mapping and variable time window amplitude (VTWA) mapping algorithms for crack visualization based on our finding that the processing direction of the adjacent wave subtraction with respect to crack orientation can dramatically affect crack visibility. The proposed MAWS, STP and VTWA mapping algorithms were implemented in a laser ultrasonic propagation imaging system and were applied in a nondestructive evaluation of an Al-alloy tank liner for space applications. A crack and void on the fusion zone of a weld were more effectively visualized using the proposed algorithms, and the crack could be visualized regardless of its orientation. The multi-directional processing results of the anomalous wave propagation imaging were visualized as video clips. The STP mapping algorithm, which maps the number of shifted time points to minimize the difference between adjacent waves, was developed to enhance the crack visualization capability of the system. Additionally, the multi-directional VTWA mapping algorithm performed data projection using the residuals of MAWS processing and provided stationary mapping results of crack-induced anomalous waves. The presented results demonstrate that the proposed visualization algorithms are promising techniques that do not overlook unknown crack orientations.

Zonally resolved impact of ENSO on the stratospheric circulation and water vapor entry values

AbstractBased on simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS) for the period 1979–2013, with model transport driven by the ECMWF ERA‐Interim reanalysis, we discuss the impact of the El Niño Southern Oscillation (ENSO) on the variability of the dynamics, water vapor, ozone, and mean age of air (AoA) in the tropical lower stratosphere during boreal winter. Our zonally resolved analysis at the 390 K potential temperature level reveals that not only (deseasonalized) ENSO‐related temperature anomalies are confined to the tropical Pacific (180–300°E) but also anomalous wave propagation and breaking, as quantified in terms of the Eliassen‐Palm (EP) flux divergence, with strongest local contribution during the La Niña phase. This anomaly is coherent with respective anomalies of water vapor (±0.5 ppmv) and ozone (±100 ppbv) derived from CLaMS being in excellent agreement with the Aura Microwave Limb Sounder observations. Thus, during El Niño a more zonally symmetric wave forcing drives a deep branch of the Brewer‐Dobson (BD) circulation. During La Niña this forcing increases at lower levels (≈390 K) over the tropical Pacific, likely influencing the shallow branch of the BD circulation. In agreement with previous studies, wet (dry) and young (old) tape recorder anomalies propagate upward in the subsequent months following El Niño (La Niña). Using CLaMS, these anomalies are found to be around +0.3 (−0.2) ppmv and −4 (+4) months for water vapor and AoA, respectively. The AoA ENSO anomaly is more strongly affected by the residual circulation (≈2/3) than by eddy mixing (≈1/3).

Aircraft Measurements and Numerical Simulations of an Expansion Fan off the California Coast

AbstractMountains along the California coastline play a critical role in the dynamics of marine atmospheric boundary layer (MBL) airflow in the vicinity of the shoreline. Large changes in the MBL topology have been known to occur downwind of points and capes along the western coast of the United States. Large spatial gradients in wind and temperature become established that can cause anomalous electromagnetic wave propagation. Detailed airborne measurements using the University of Wyoming King Air were conducted to study the adjustment of the MBL to the Point Arguello and Point Conception headlands. Pronounced thinning of the MBL consistent with an expansion fan occurred to the south of Point Conception on 13 June 2012. A sharp cloud edge was collocated with the near collapse of the MBL. D-value cross sections derived from differential GPS altitude measurements allow assessment of the vertical profile of the horizontal pressure gradient force and hence thermal wind forcing in response to the near collapse of the MBL. The Weather Research and Forecasting Model was run with a 1-km grid spacing to examine the atmospheric adjustment around Point Conception during this period. Results from the simulations including the vertical cross sections of the horizontal pressure gradient force were consistent with the aircraft observations. Model results suggest that divergence occurs as the flow rounds Point Conception, characteristic of an expansion fan. Wind speeds in the MBL increase coincident with the decrease in MBL thickness, and subsiding flow associated with the near collapse of the MBL is responsible for the sharp cloud edge.