Magnetoacoustic Research Articles

A Parametric Study of Locally Generated Magnetosonic Waves by Ring‐Beam Hot Protons in the Martian Heavy Ion‐Rich Environment

AbstractMagnetosonic (MS) waves with frequencies above the proton gyrofrequency can be locally generated by ring‐beam protons in the Martian heavy ion‐rich ionosphere. In this study, we conduct a parametric analysis to investigate the effects of heavy ion concentrations, energy (Erb), and angle (αrb) of ring‐beam protons, and wave normal angle on the excitation features of Martian ionospheric MS waves. We find the growth rates and frequency range of MS waves decrease by including O+ and O2+ ions but are insensitive to their relative concentrations. With increasing Erb or αrb, the growth rates of MS waves show a general dropping tendency. Meanwhile, their frequency and wavenumber range are almost unaffected by increasing Erb but shrink to a narrower range mainly distributed in high frequencies by increasing αrb. Unstable MS waves expand to a wider wavenumber range but shrink to a narrower frequency range as they become more oblique.

Effect of area divergence and frequency on damping of slow magnetoacoustic waves propagating along umbral fan loops

ABSTRACT Waves play an important role in the heating of solar atmosphere; however, observations of wave propagation and damping from the solar photosphere to corona through chromosphere and transition region are very rare. Recent observations have shown propagation of 3-min slow magnetoacoustic waves (SMAWs) along fan loops from the solar photosphere to corona. In this work, we investigate the role of area divergence and frequencies on the damping of SMAWs propagating from the photosphere to the corona along several fan loops rooted in the sunspot umbra. We study the Fourier power spectra of oscillations along fan loops at each atmospheric height which showed significant enhancements in 1–2, 2.3–3.6, and 4.2–6 min period bands. Amplitude of intensity oscillations in different period bands and heights are extracted after normalizing the filtered light curves with low-frequency background. We find damping of SMAW energy flux propagating along the fan loop 6 with damping lengths $\approx 170$ and $\approx 208$ km for 1.5- and 3-min period bands. We also show the decay of total wave energy content with height after incorporating area divergence effect, and present actual damping of SMAWs from photosphere to corona. Actual damping lengths in this case increases to $\approx 172$ and $\approx 303$ km for 1.5- and 3-min period bands. All the fan loops show such increase in actual damping lengths, and thus highlight the importance of area divergence effect. Results also show some frequency-dependent damping of SMAW energy fluxes with height where high-frequency waves are damped faster than low-frequency waves.

Artificial excitation and propagation of ultra-low frequency signals in the polar ionosphere

This paper has established a relatively comprehensive model for ultra-low frequency (ULF) current induced by thermal pressure gradients and its propagation. In the ULF current excitation model, we decomposed the current into a constant term unaffected by altitude and a product with a function significantly influenced by altitude. Combining this with the EISCAT background, we determined that for modulation frequencies below 5 Hz, the optimal height for ULF current excitation corresponds to the critical frequency height. We calculated the ionospheric currents at heating altitudes of 332 km for modulation frequencies of 5 Hz; the corresponding maximum currents were 1.03 × 10−10 A·m−2. By incorporating the current into the ULF waves propagation model based on magnetoionic theory, we found that the electromagnetic field energy is mainly concentrated in the horizontal direction, indicating that the energy primarily propagates outward through magnetosonic waves. The dominant components are the electric field component Ey and the magnetic field component Bz, whose maximum values reached 1.1 μV·m−1 and 1.5 pT. Unfortunately, magnetosonic waves cannot propagate downward due to the sharp variation in the real part of the refractive index between 200 and 300 km. However, the shear Alfvén waves component By can propagate downward, and there is still an intensity of approximately 0.1 pT at the bottom of the ionosphere, which is because the refractive index of shear Alfvén waves is most uniform in the parallel magnetic field direction, allowing By to propagate parallel to the magnetic field effectively.

Magnetosonic shock waves in degenerate electron–positron–ion plasma with separated spin densities

This study investigates magnetosonic shock waves in a spin-polarized three-component quantum plasma using the quantum magnetic hydrodynamic model. We explore the influence of spin effects, specifically spin magnetization current and spin pressure, on shock wave behavior. Numerical analysis of the linear dispersion relation under varying parameters such as positron imbalance, spin polarization ratio, plasma beta, quantum diffraction, and magnetic diffusivity reveals differential impacts, with diffusion exerting significant influence on the plasma frequency. Our findings highlight the sensitivity discrepancy between the real and imaginary parts of the dispersion relation. Furthermore, nonlinear behavior of magnetosonic shock waves is examined via the Korteweg–de Vries–Burgers equation, showcasing transitions between oscillatory and monotonic wave patterns based on changes in dimensionless parameters. Notably, we observe the combined effects of spin-up and spin-down positrons with spin-up and spin-down electrons on shock wave dynamics, contributing to a deeper understanding of spin-plasma interactions with implications across various fields.

[formula omitted]-soliton solutions of coupled Schrödinger–Boussinesq equation with variable coefficients

In this paper, soliton solutions of the coupled variable coefficients Schrödinger–Boussinesq equation, which describes the stationary propagation of coupled upper-hybrid waves and magnetoacoustic waves in a magnetized plasma, are investigated. Based on the Hirota bilinear method, the bilinear form, one, two, three and N-soliton solutions of Schrödinger–Boussinesq equation are derived. By means of numerical calculation, the specific figures of different soliton solutions are obtained by selecting different coefficients. The propagation and interaction of the soliton solutions are analyzed graphically.

Modulation instability of magnetosonic waves in semiconducting quantum plasma considering Fermi degenerate pressure, exchange correlation potential, and Bohm potential

This study investigates the modulation instability of magnetosonic waves in a semiconducting quantum plasma system. Utilizing the quantum hydrodynamic model, we derive the nonlinear Schrödinger equation and its solution through the reductive perturbation technique. The growth rate of modulation instability for magnetosonic waves has been derived. This study incorporates various quantum corrections, including Fermi degenerate pressure, exchange-correlation potential, and Bohm potential. We study the bright soliton profiles of magnetosonic waves, and additionally, we conduct graphical analyses of the linear dispersion relation and the product of the dispersive coefficient (P) and nonlinear coefficient (Q) of the nonlinear Schrödinger equation. It has been found that magnetosonic waves exhibit modulation instability within specific parameter ranges of the semiconductor plasma and at certain wavelength regimes. Further, we present a comparative study between GaSb and InSb semiconducting plasma systems. The exchange-correlation potential and Fermi degenerate pressure have significantly impacted the modulation instability growth rate, whereas the effect of the Bohm potential is much lower.

First Observation of Harmonics of Magnetosonic Waves in Martian Magnetosheath Region

AbstractThe present study provides an evidence for the generation of harmonics of magnetosonic waves in the Martian magnetosheath region. The wave signatures are manifested in the magnetic field measurements recorded by the fluxgate magnetometer instrument onboard the Mars Atmosphere and Volatile Evolution missioN (MAVEN) spacecraft in the dawn sector around 5–10 LT at an altitude of 4,000–6,000 kms. The wave that is observed continuously from 19.1 to 20.7 UT below the proton cyclotron frequency (fci ≈ 46 mHz) is identified as fundamental mode of the magnetosonic wave. Whereas harmonics of the magnetosonic wave are observed during 19.7–20.3 UT at frequencies that are multiple of fci. The ambient solar wind proton density and plasma flow velocity are found to vary with a fundamental mode frequency of 46 mHz. It is noticed that the fundamental mode is mainly associated with the left‐hand (LH), and higher frequency harmonics are associated with the right‐hand (RH) circular polarizations. A clear difference in the polarization and ellipticity is noticed during the time of occurrence of harmonics. The magnetosonic wave harmonics are found to propagate in the quasi‐perpendicular directions to the ambient magnetic field. The results of linear theory and Particle‐In‐Cell simulation performed here are in agreement with the observations. The present study provides a conclusive evidence for the occurrence of harmonics of magnetosonic wave in the close vicinity of the magnetosheath region of the unmagnetized planet Mars.

Study of Differences in the Dispersion of Transverse Harmonics of Slow Magnetoacoustic Waves Propagating in Coronal Loops

Study of Differences in the Dispersion of Transverse Harmonics of Slow Magnetoacoustic Waves Propagating in Coronal Loops

Localizing Quasiperiodic Pulsations in Hard X-Ray, Microwave, and Lyα Emissions of an X6.4 Flare

We report the simultaneous observations of quasiperiodic pulsations (QPPs) in wavelengths of hard X-ray (HXR), microwave, Lyα, and ultraviolet (UV) emissions during the impulsive phase of an X6.4 flare on 2024 February 22 (SOL2024-02-22T22:08). The X6.4 flare shows three repetitive and successive pulsations in HXR and microwave wavebands, and they have an extremely large modulation depth. The onset of flare QPPs is almost simultaneous with the start of magnetic cancellation between positive and negative fields. The wavelet power spectra suggest the presence of double periods, which are centered at ∼200 and ∼95 s, respectively. The long-period QPP can also be detected in Lyα and UV wavebands at the flare area, and it could be observed in the adjacent sunspot. Our observations indicate that the flare QPPs are most likely triggered by accelerated electrons that are associated with periodic magnetic reconnections. The long period at ∼200 s is probably modulated by the slow magnetoacoustic wave originating from the neighboring sunspot, while the short period at ∼95 s could be regarded as its second harmonic mode.

Multi-wavelength Observations of Umbral Oscillations above a Sunspot

We investigate the umbral oscillation at multi-height solar atmospheres above a sunspot in the active region of National Oceanic and Atmospheric Administration 12680 on 2017 September 15. In this study, the extreme ultraviolet images were measured by the Atmospheric Imaging Assembly (AIA), while the ultraviolet spectral lines and images were observed by the Interface Region Imaging Spectrograph. At the sunspot umbra, the AIA 1700 Å intensity curve shows the primary oscillation with a long period of ∼(4.2±0.8) minutes, while the intensity curves in AIA 1600 Å, 171 Å, and 193 Å exhibit an apparent oscillation with a short period of ∼(2.8±0.3) minutes. Meanwhile, a short period of ∼(3.1±0.5) minutes is found in the Mg II h & k lines and the slit-jaw image at 2796 Å, a short period of ∼(2.9±0.4) minutes is detected in the Si IV 1393.76 Å line. Our observations suggest that the oscillatory periods at the sunspot umbra decrease with the height of solar outer atmospheres. The short period is roughly equal to 3 minutes, which could be interpreted as the propagating slow magnetoacoustic wave above the sunspot umbra, and it might originate from the temperature minimum region and then propagate up to the corona. While the long period is close to 5 minutes oscillation in the photosphere, which might be regarded as the solar P-mode wave.

Modeling the Propagation of Slow Magnetoacoustic Waves in a Multistranded Coronal Loop

We study the propagation properties of slow magnetoacoustic waves in a multithermal coronal loop using a 3D MHD model, for the first time. A bundle of 33 vertical cylinders, each of 100 km radius, randomly distributed over a circular region of radius 1 Mm, is considered to represent the coronal loop. The slow waves are driven by perturbing the vertical velocity (v z ) at the base of the loop. We apply forward modeling to the simulation results to generate synthetic images in the coronal channels of the Solar Dynamics Observatory/Atmospheric Imaging Assembly. Furthermore, we add appropriate data noise to enable direct comparison with the real observations. It is found that the synthetic images at the instrument resolution show noncospatial features in different temperature channels in agreement with previous observations. Time–distance maps are constructed from the synthetic data to study the propagation properties. The results indicate that the oscillations are only visible in specific channels, depending on the temperature range of the plasma existing within the loop. Additionally, the propagation speed of slow waves is also found to be sensitive to the available temperature range. Overall, we propose that the cross-field thermal properties of coronal structures can be inferred using a combination of numerical simulations and observations of slow magnetoacoustic waves.

Pioneer Venus Orbiter Observations of Solar Wind Driven Magnetosonic Waves Interacting With the Dayside Venusian Ionosphere

AbstractWe use in situ plasma observations made by the Pioneer Venus Orbiter spacecraft to show for the first time that magnetosonic waves can couple the solar wind to the upper ionosphere and deposit energy there. The waves are generated upstream of Venus, are advected into the shock and propagate across the draped magnetic field, through the magnetosheath and into the dayside upper ionosphere. The magnetosonic waves damp in the upper ionosphere in a region where physical collisions are rare, and electromagnetic forces must control this damping. The waves damp when the ionospheric heavy ion density is a few thousand cm−3 and wave‐particle interactions with the dominant O+ ions are postulated as the damping mechanism. Estimates of ion heating rates show that 1%–5% of the O+ ion distribution function could be heated to escape energy in 10–40 s.

The Transfer of Solar Wind Energy to the Venusian Ionosphere Through Magnetic Pumping: Evidence From Pioneer Venus Orbiter Observations

AbstractThe collisionless nature of planetary magnetospheres means that electromagnetic forces are fundamental in controlling the flow of energy and momentum through these systems. We use Pioneer Venus Orbiter (PVO) observations to demonstrate that the magnetic pumping process can be active at Venus, in analogy to its recent discovery at Mars. The presented case study demonstrates the framework for how the process can work at Venus, and the results of a statistical analysis show that the ambient plasma conditions support the process being active. Magnetic pumping enables low frequency magnetosonic waves to heat ambient ionospheric electrons and provides a mechanism that couples the solar wind to the Venusian ionosphere. This is the first time the magnetic pumping process has been discussed at Venus.

Study of the magnetoelastic effect in nickel and cobalt thin films at GHz range using x-ray microscopy

We use surface acoustic waves of 1 and 3 GHz in hybrid piezoelectric-magnetic systems with either nickel or cobalt as a magnetic layer to generate magnetoacoustic waves and directly image them using stroboscopic x-ray magnetic circular dichroism imaging. Our measurements visualize and quantify the amplitudes of both acoustic and magnetic components of the magnetoacoustic waves, which are generated in the ferromagnetic layer and can propagate over millimeter distances. Additionally, we quantified the magnetoelastic strain component for nickel and cobalt through micromagnetic simulations. Published by the American Physical Society 2024

Resonant and nonresonant excitation of waves in a planar magnetosonic flow

AbstractForced propagation of perturbations in a magnetosonic wave are considered. The driving force may be caused by stimulated Mandelstam–Brillouin scattering of optic waves or by intense magnetosonic exciter. Some heating‐cooling function which takes into account radiative cooling and unspecified heating is taken into consideration, as well as nonlinearity of a medium. Both these factors make the excitation particular. The analytical and numerical evaluations reveal that forced oscillations differ essentially from the free propagation and depend on a number of dimensionless parameters such as the ratio of speed of exciter to the eigen speed of excited wave, the ratio of speed of an excited wave to its eigen speed, and the dimensionless magnitude of an exciter. Forced excitation is resonant if speed of an exciter coincides with the eigen speed of excited wave but may give rise to the excited perturbations with the speed different from the eigen one. The preliminary evaluations may be helpful for the controlled excitation of perturbations in natural and laboratory plasma systems and indication of the parameters of an exciter.

A New Model of Electron Pitch Angle Distributions and Loss Timescales in the Earth's Radiation Belts

AbstractAs the number of satellites on orbit grows it is increasingly important to understand their operating environment. Physics‐based models can simulate the behavior of the Earth's radiation belts by solving a Fokker‐Planck equation. Three‐dimensional models use diffusion coefficients to represent the interactions between electromagnetic waves and the electrons. One‐dimensional radial diffusion models neglect the effects of energy diffusion and represent the losses due to the waves with a loss timescale. Both approaches may use pitch angle distributions (PADs) to create boundary conditions, to map observations from low to high equatorial pitch angles and to calculate phase‐space density from observations. We present a comprehensive set of consistent PADs and loss timescales for 2 ≤ L* ≤ 7, 100 keV ≤ E ≤ 5 MeV and all levels of geomagnetic activity determined by the Kp index. These are calculated from drift‐averaged diffusion coefficients that represent all the VLF waves that typically interact with radiation belt electrons and show good agreement with data. The contribution of individual waves is demonstrated; magnetosonic waves have little effect on loss timescales when lightning‐generated whistlers are present, and chorus waves contribute to loss even in low levels of geomagnetic activity. The PADs vary in shape depending on the dominant waves. When chorus is dominant the distributions have little activity dependence, unlike the corresponding loss timescales. Distributions peaked near 90° are formed by plasmaspheric hiss for L* ≤ 3 and E < 1 MeV, and by EMIC waves for L* > 3 and E > 1 MeV. When hiss dominates, increasing activity broadens the distribution but when EMIC waves dominate increasing activity narrows the distribution.

Reflection Coefficient for Two‐Dimensional Propagation of Fast Magnetosonic Waves Emerging One‐Dimensional Mesoscale Density Boundaries

AbstractIn recent studies, two‐dimensional propagation model of fast magnetosonic (MS) waves has been proposed to interpret the satellite observations of MS waves knocking into a density boundary. Although the theoretical model is able to capture the main properties of the two‐dimensional propagation of MS waves, quantitative description about the MS wave behaviors has not been given yet. Here, with the assumption of a parabolic function for the potential function near its minimum, we solve the wave equation only with a potential function to obtain the reflection coefficients. It is found that the wave equation with a potential function can describe the full reflection and full transmission of MS waves rather well. Furthermore, the first‐order derivative term in the wave equation is utilized to modify the reflection coefficient when the minimum of the potential function is near zero. Our result is helpful for further understanding the two‐dimensional propagation of MS waves.

The effects of plasma density structure on the propagation of magnetosonic waves: 1-D particle-in-cell simulations

Magnetosonic (MS) waves, i.e., ion Bernstein mode waves, are one of the common plasma waves in the Earth’s magnetosphere, which are important for regulating charged particle dynamics. How MS waves propagate in the magnetosphere is critical to understanding the global distribution of the waves, but it remains unclear. Although previous studies present that MS waves can be reflected by fine-scale density structures, the dissipation of waves by background plasma has long been neglected. In this study, we perform one-dimensional (1-D) particle-in-cell (PIC) simulations to study the propagation of MS waves through density structures, where both absorption and reflection have been included. We find that absorption is as important as reflection when considering the propagation of MS waves through density structures, and both of them are strongly dependent on the shape of density structures. Specifically, the reflectivity of MS waves is positively and negatively correlated with the height and width of density structures, respectively, while the absorptivity of MS waves has a positive correlation with both the height and width of density structures. Our study demonstrates the significance of absorption during the propagation of MS waves, which may help better understand the distribution of MS waves in the Earth’s magnetosphere.

Migration of Fast Magnetosonic Waves in the Magnetosphere With a Plasmaspheric Plume

AbstractPlasmaspheric density structures are considered to control the propagation trajectories of fast magnetosonic (MS) waves in the inner magnetosphere. However, whether the plasmaspheric plume can effectively alter the propagation of MS waves remains unknown. Based on the analytical model of plasma density, ray tracing simulations are performed to investigate the propagation of exactly perpendicular MS waves in the equatorial plane in the magnetosphere containing a plasmaspheric plume. We find that plasmatrough and plume MS waves propagating toward the plasmaspheric plume can be reflected into the plasmaspheric core by the plume, then potentially migrating globally and thus quasi‐trapped inside the plasmaspheric core. The simulations also indicate that lower‐frequency MS waves approaching the plasmaspheric plume are more easily reflected and quasi‐trapped inside the plasmaspheric core. Our findings illustrate a previously unexplored way that plasmatrough MS waves could access and be trapped inside the plasmaspheric core via azimuthal plasmaspheric density structures.

An Additional Note to “A New Insight into the Linear Theory of Magnetoacoustic Waves in the Homogeneous Flux Tubes with an Abrupt Boundary”

This is to address the criticism expressed in the article (Goedbloed & Poedts ) referred to as GP[24] about the work (Yelagandula ) referred to as Y[23]. It will be shown that the dispersion relation obtained in Y[23] is indeed correct within the framework of the ZSER model discussed in Y[23] despite the correct criticism of GP[24] about the electrodynamic boundary condition.