Anomalous Propagation Research Articles

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.

Anomalous microwave propagation interpreted by the weak-measurement theory

In the light of new experimental results of microwave propagation in the near field, we demonstrate that, in addition to a standard electromagnetic description, the results obtained can be interpreted as a case of “weak measurement”. In this framework, the analysis is performed in a similar way to the one already carried out for interpreting optical tunneling.

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.

Anomalous propagation and scattering of sound in 2-propanol water solution near its singular point

In this study we describe the anomalous physical properties of aqueous alcohol solutions near its singular (particular) points. A special attention is paid to conducting experiments on the temperature (T), concentration (x) and frequency (f) dependence of the sound velocity and effective absorption coefficient in a binary mixture 2-propanol – water in wide intervals of T=(293÷343) K, x=(0÷1) of 2-propanol molar fractions, and f=(10÷2500) MHz. A singular (particular) point of 2-propanol-water solution with coordinate xs=0.03±0.01, Ts=(313.0±2.0)K is found as the intersection points of the sound velocity and absorption coefficient dependence on concentration and temperature at different frequencies. An anomalous behavior of aqueous alcohol solutions near the singular (particular) points enables us to support the hypothesis of the “fluctuating clusters mechanism”. This finding can directly explain two important effects as follows: an anomalous growth of (a) the light molecular scattering and (b) the sound molecular scattering.

Ensemble Classification for Anomalous Propagation Echo Detection with Clustering-Based Subset-Selection Method

Several types of non-precipitation echoes appear in radar images and disrupt the weather forecasting process. An anomalous propagation echo is an unwanted observation result similar to a precipitation echo. It occurs through radar-beam ducting because of the temperature, humidity distribution, and other complicated atmospheric conditions. Anomalous propagation echoes should be removed because they make weather forecasting difficult. In this paper, we suggest an ensemble classification method based on an artificial neural network and a clustering-based subset-selection method. This method allows us to implement an efficient classification method when a feature space has complicated distributions. By separating the input data into atomic and non-atomic clusters, each derived cluster will receive its own base classifier. In the experiments, we compared our method with a standalone artificial neural network classifier. The suggested ensemble classifier showed 84.14% performance, which was about 2% higher than that of the k-means clustering-based ensemble classifier and about 4% higher than the standalone artificial neural network classifier.

見通し内VHF帯放送波の伝搬異常と地震及び地表面平均風速の統計的関連性

見通し内VHF帯放送波の伝搬異常と地震及び地表面平均風速の統計的関連性

Limits on the Anomalous Speed of Gravitational Waves From Binary Pulsars

A large class of modified theories of gravity used as models for dark energy predict a propagation speed for gravitational waves which can differ from the speed of light. This difference of propagations speeds for photons and gravitons has an impact in the emission of gravitational waves by binary systems. Thus, we revisit the usual quadrupolar emission of binary system for an arbitrary propagation speed of gravitational waves and obtain the corresponding period decay formula. We then use timing data from the Hulse-Taylor binary pulsar and obtain that the speed of gravitational waves can only differ from the speed of light at the percentage level. This bound places tight constraints on dark energy models featuring an anomalous propagations speed for the gravitational waves.

Velocity autocorrelation function in supercooled liquids: Long-time tails and anomalous shear-wave propagation.

Molecular dynamic simulations are performed to reveal the long-time behavior of the velocity autocorrelation function (VAF) by utilizing the finite-size effect in a Lennard-Jones binary mixture. Whereas in normal liquids the classical positive t^{-3/2} long-time tail is observed, we find in supercooled liquids a negative tail. It is strongly influenced by the transfer of the transverse current wave across the period boundary. The t^{-5/2} decay of the negative long-time tail is confirmed in the spectrum of VAF. Modeling the long-time transverse current within a generalized Maxwell model, we reproduce the negative long-time tail of the VAF, but with a slower algebraic t^{-2} decay.

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.

Automatic system for radar echoes filtering based on textural features and artificial intelligence

Among the very popular Artificial Intelligence (AI) techniques, Artificial Neural Network (ANN) and Support Vector Machine (SVM) have been retained to process Ground Echoes (GE) on meteorological radar images taken from Setif (Algeria) and Bordeaux (France) with different climates and topologies. To achieve this task, AI techniques were associated with textural approaches. We used Gray Level Co-occurrence Matrix (GLCM) and Completed Local Binary Pattern (CLBP); both methods were largely used in image analysis. The obtained results show the efficiency of texture to preserve precipitations forecast on both sites with the accuracy of 98% on Bordeaux and 95% on Setif despite the AI technique used. 98% of GE are suppressed with SVM, this rate is outperforming ANN skills. CLBP approach associated to SVM eliminates 98% of GE and preserves precipitations forecast on Bordeaux site better than on Setif’s, while it exhibits lower accuracy with ANN. SVM classifier is well adapted to the proposed application since the average filtering rate is 95–98% with texture and 92–93% with CLBP. These approaches allow removing Anomalous Propagations (APs) too with a better accuracy of 97.15% with texture and SVM. In fact, textural features associated to AI techniques are an efficient tool for incoherent radars to surpass spurious echoes.

Escape and trapping of low-frequency gravitationally lensed rays by compact objects within plasma

We consider the gravitational lensing of rays emitted by a compact object (CO) within a distribution of plasma with power-law density $\propto r^{-h}$. For the simplest case of a cloud of spherically symmetric cold non-magnetized plasma, the diverging effect of the plasma and the converging effect of gravitational lensing compete with one another. When $h<2$, the plasma effect dominates over the vacuum Schwarzschild curvature, potentially shifting the radius of the unstable circular photon orbit outside the surface of the CO. When this occurs, we define two relatively narrow radio-frequency bands in which plasma effects are particularly significant. Rays in the escape window have $\omega_{0} < \omega \leq \omega_{+}$ and are free to propagate to infinity from the CO surface. To a distant observer, the visible portion of the CO surface appears to shrink as the observed frequency is reduced, and vanishes entirely at $\omega_{0}$, in excess of the plasma frequency at the CO surface. We define the anomalous propagation window for frequencies $\omega_{-}< \omega \leq \omega_{0}$. Rays emitted from the CO surface within this frequency range are dominated by optical effects from the plasma and curve back to the surface of the CO, effectively cloaking the star from distant observers. We conclude with a study of neutron star (NS) compactness ratios for a variety of nuclear matter equations of state (EoS). For $h=1$, NSs generated from stiff EoS should display significant frequency dependence in the EW, and lower values of $h$ with softer EoS can also show these effects.

Anomalous propagation of VHF radiowaves behind the horizon in the seismic region

A theory of electromagnetic radiation generation by random electric discharges in the troposphere and VHF radiowave scattering by these discharges has been developed. The discharge model, which makes it possible to calculate the spatiotemporal distribution of the discharge channel conductivity depending on the electric current value in this discharge, has been obtained. The electromagnetic radiation spectrum in the troposphere occupied by random discharges has been calculated. VHF electromagnetic wave scattering by random electric discharges in the troposphere has been considered. Equations have been derived, and the method for calculating the average value of the electromagnetic wave field scattered by random discharges has been developed. The calculations indicated that the scattered wave field amplitude is much larger than the diffraction wave field amplitude behind the horizon. The theoretical results agree with the observations of the electromagnetic radiation and VHF transmitter signals behind the horizon relative to the earthquake epicenter during the earthquake preparation.

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).

The Seasonal and Diurnal Cycles of Refractivity and Anomalous Propagation in the Sahelian Area from Microwave Radiometric Profiling

AbstractThe Sahelian zone of West Africa is a semiarid area where strong amplitude of the seasonal and diurnal cycles of water vapor and temperature is observed. One year of continuous observation of vertical profiles of water vapor and temperature gathered from Niamey, Niger, with a profiling microwave radiometer is used to analyze the climatology of refractivity and microwave propagation regimes in the low troposphere. Seasonal and diurnal cycles of refractivity and ground-based radar anomalous propagation are emphasized. It is shown that the combined effect of water vapor and temperature vertical gradients is responsible for strong seasonal and diurnal cycles of the ducting propagation regime. Statistics of propagation regimes are given. The probability density functions of the refractivity gradient are found lognormally distributed. Three months of C-band radar data simultaneous with the profiling microwave radiometer observations have also been collected. Relations between the vertical refractivity gradient and the ground-based radar anomalous propagation echoes (APE) are illustrated and discussed. APE spatial distributions are found strongly related to the main features of the orography and topography inside the radar-observed area. Contingency tests show that the probability for APE to be linked to ducting is higher than 95%. In addition, this paper suggests that observing the refractivity vertical profiles from a microwave radiometer profiler located close to a meteorological radar provides information on whether anomalous propagation has to be considered as a potential cause of spurious signal in the measured reflectivity field.

Duct heights inferred from radar sea clutter using proper orthogonal bases

Maritime electromagnetic (EM) based communication and detection systems are strongly influenced by meteorological conditions, as they can cause anomalous electromagnetic propagation within the surface layer. To predict the performance of such systems, detailed knowledge of the refractivity profile is required. In recent years, refractivity from clutter (RFC) methods have been developed to estimate this refractivity profile by measuring radar clutter return from the rough ocean surface. The current work proposes an RFC framework that utilizes a novel surrogate model for EM propagation. The surrogate model is based on an offline created library of sparsely sampled field data of clutter returns, compressed into proper orthogonal bases, and indexed on specific surface layer refractive parameters. By exploiting the Riemannian manifold structure of the space that proper orthogonal bases occur in, we are able to interpolate among them. This, then, enables us to use the surrogate model in an inverse problem setting, whose goal is to uncover in situ maritime EM propagation conditions efficiently. We demonstrate the feasibility of our proposed surrogate model-based RFC approach for evaporation duct by testing it with field data obtained from an experimental campaign.

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.

Linear and anomalous front propagation in systems with non-Gaussian diffusion: The importance of tails.

We investigate front propagation in systems with diffusive and subdiffusive behavior. The scaling behavior of moments of the diffusive problem, both in the standard and in the anomalous cases, is not enough to determine the features of the reactive front. In fact, the shape of the bulk of the probability distribution of the transport process, which determines the diffusive properties, is important just for preasymptotic behavior of front propagation, while the precise shape of the tails of the probability distribution determines asymptotic behavior of front propagation.

An Efficient Approach for Ground Echoes Suppression Based on Textural Features and SVM

The use of the Support Vector Machine (SVM) technique for the clutter identification in the context of meteorological data is presented. The clutter is due to ground echoes and anomalous propagation. The SVM is combined with textural approach which is based on the Grey Level Co-occurrence Matrix (GLCM) that is the most used in the textural analysis image. An incoherent radar site is considered for this study. The results reveal that over than 91.1% of ground echoes are identified and 90.3% of precipitations are preserved. In addition 95.99% of anomalous propagation are removed. The use of our approach is lasts than 1mn for the treatment of each image. We can then filter the radar image in real time

Anomalous phenomena on HF radio paths during geomagnetic disturbances

We analyze ionospheric oblique sounding data on three high-latitude and one high-latitude–midlatitude HF radio paths for February 15 and 16, 2014, when two substorms and one magnetic storm occurred. We investigate cases of anomalous propagation of signals: their reflection from sporadic layer Es, lateral reflections, type “M” or “N” modes, the presence of traveling ionospheric disturbances, and the diffusivity of signals and triplets. The most significant results are the following. In geomagnetically undisturbed times, sporadic Es-layers with reduced maximum observed frequencies (MOFEs) on three high-latitude paths were observed in both days. The values of MOFEs during disturbances are large, which leads to the screening of other oblique sounding signals reflected from the ionosphere. On all four paths, the most frequently traveling ionospheric disturbances due to the terminator were observed in quiet hours from 03:00 to 15:00 UT on the first day and from 06:00 to 13:00 UT on the second day of the experiment. In addition, both the sunset terminator and the magnetic storm on the high-latitude–mid-latitude path were found to generate traveling ionospheric disturbances jointly. No such phenomenon was found on high-latitude paths.

Anomalous propagation conditions over eastern Pacific Ocean derived from MAGIC data

AbstractThis study characterizes the evaporation and elevated ducts, the most common types of ducts observed over the ocean, along a track of around 4000 km between the California coast and Hawaii. We analyzed 1 year (2012–2013) of ship‐based measurements made during the Marine Atmospheric Radiation Measurement GPCI (GEWEX cloud system study Pacific Cross‐Section Intercomparison) Investigation of Clouds (MAGIC) campaign. During this period, the ship made multiple transects between Southern California and Hawaii. While the ship‐based in situ measurements and the radiosonde data served as the primary data source, a marine atmospheric surface layer model adapted from the Coupled Ocean‐Atmosphere Response Experiment 3.0 surface flux scheme is used to diagnose evaporative duct properties. Calculated mean evaporation duct heights based on shipboard measurements were found to increase steadily from 7 m offshore California to about 15 m near Hawaii. Overall 78% of duct heights are below 20 m. On average the evaporation duct strength is between ≈ 25 and 35 M units near Hawaii and about 15 M units near the California coast. A gradual transition from stratocumulus (Sc) dominated offshore California to trade wind regime with cumulus (Cu) clouds takes place along MAGIC track. The measured marine atmospheric boundary layer (MABL) height and the capping inversion characteristics are significantly different in the two regimes with MABL decoupling occurring in the longitude range between 125°W and 140°W along the track. The characteristics of the elevated ducts, obtained from the rawinsonde sounding profiles, are also different in the two regions west and east of the MABL decoupling region. Approximately 70–80% of the elevated ducts occur below 1.5 km east of the decoupling region, whereas almost equal percentage of ducts forms at heights above 1.5 km on the west side.