arXiv subjects

A. P. Misra

Publications and source records attributed to A. P. Misra.

At least 19 recordsLinked to original sources

arXiv2026

Gravitational instability in partially ionized plasmas: A two-fluid approach

We propose a new two-fluid model for a partially ionized magnetoplasma under gravity, in which electrons and neutrals are treated as a single fluid, while singly charged positive ions are a separate fluid. We observe that the classical result of gravitational instability (also known as Rayleigh-Taylor instability) in fully ionized plasmas becomes significantly modified by the influence of ion-neutral collisions (with frequency $ν_{\rm{in}}$) and transverse wave numbers ($k_x$ and $k_y$). The instability growth rate can be enhanced or decreased depending on the values of the ratios $κ\equiv k_x/k_y$ and $f\equivν_{\rm{in}}/Ω_{\rm{ci}}$, where $Ω_{\rm{ci}}$ is the ion-cyclotron frequency. We also estimate the growth rates relevant to the ionospheric E-region and solar atmosphere, noting that such growth rates can have a maximum for $κ,~f\ll1$, or for $κ>1$ and $f\sim0.64$, and minimized for $f\gg1$ irrespective of the value of $κ$. Furthermore, the timescale of instability ranges from $1$ minute to $2$ minutes in the solar atmosphere, while in the E region, it ranges from $1$ minute to $80$ minutes. The latter can be a satisfactory result for the reported lifetime of solar prominence threads.

physics.plasm-ph↗

arXiv2026

Chaos in the dynamics of electromagnetic solitons in relativistic degenerate plasmas

We propose a coupled system for the nonlinear interaction between high-frequency, circularly polarized, intense electromagnetic (EM) waves and low-frequency electron-density perturbations, driven by the EM-wave ponderomotive force, in an unmagnetized plasma composed of fully degenerate relativistic electrons and stationary positive ions, including a higher-order correction to the nonlocal nonlinearity. We show that the modulational instability (MI) growth rate associated with the generation of EM envelope solitons gets significantly reduced with a slight increase in either the nonlocal nonlinear correction or the degeneracy parameter. Furthermore, a three-wave temporal model predicts the existence of quasiperiodic and chaotic states of EM solitons while interacting with longitudinal electron density perturbations. We show that the greater the degeneracy (or the higher the contribution from the nonlocal correction), the smaller the instability domain of modulation wave numbers; thus, degeneracy favors the stability of EM soliton evolution. The existence of temporal chaos in a low-dimensional model could be a signature of the development of spatiotemporal chaos in the complete nonlinear model, in which many electromagnetic solitons can be excited and saturated as they interact with electron plasma waves.

physics.plasm-ph↗

arXiv2026

Pattern formation and spatiotemporal chaos in relativistic degenerate plasmas

We numerically study the nonlinear interactions of high-frequency circularly polarized electromagnetic (EM) waves and low-frequency electron-acoustic (EA) density perturbations driven by the EM wave ponderomotive force in relativistic plasmas {(moderate, strong, and ultra-relativistic)} with two groups of electrons--the population of relativistic degenerate dense electrons (bulk plasma) and the sparse relativistic nondegenerate (classical) electrons, and immobile singly charged positive ions. By pattern selection, we show that many solitary patterns can be generated and drenched through modulational instability of EM waves at different spatial length scales and that the EM wave radiation spectra emanating from compact astrophysical objects may not settle into stable envelope solitons but into different incoherent states, including the emergence of temporal and spatiotemporal chaos due to collisions and fusions among the patterns with strong EA wave emission. The appearance of these states is confirmed by analyzing the Lyapunov exponent spectra, correlation function, and mutual information {as quantitative evidence}. As a result, the redistribution of wave energy from initially exciting many solitary patterns at large scales to a few new incoherent patterns with small wavelengths in the system occurs, leading to the onset of turbulence in astrophysical plasmas.

physics.plasm-ph↗

arXiv2025

Ion-beam driven dust-cyclotron and dust-lower-hybrid instabilities in nonthermal dusty magnetoplasmas with dust-charge fluctuation

We reveal a new dispersive dust-lower-hybrid (DLH)-like mode that can couple to modified dust-cyclotron (DC) waves in a dusty magnetoplasma by the influence of a streaming ion beam. Previous studies have overlooked such hybrid modes and the coupling in the study of resonant cyclotron instabilities in dusty magnetoplasmas. Using two-fluid models for positive ion beams and charged dust grains, nonthermal $κ$-density distributions for electrons and positive ions, and orbital motion limited (OML) models for dust-charge fluctuations, we derive a general linear dispersion relation for the coupled DLH and DC modes in the limit of when the hydrodynamic time scale is much longer than the dust-charging time scale. The hybrid mode propagates with a frequency lower than the typical dust-lower-hybrid frequency, $\widetildeω_{\rm{dl}}\equivω_{\rm{pd}}Ω_d/\sqrt{ω^2_{\rm{pd}}+Ω^2_d}$, where $ω_{\rm{pd}}$ is the dust-plasma oscillation frequency and $Ω_d$ is the dust-cyclotron frequency. We obtain the growth rates of instabilities due to Cerenkov and cyclotron interactions and analyze them, taking into account the influences of the static magnetic field, ion-to-electron temperature ratio, electron-to-dust number density ratio, dust-charge fluctuation, and superthermal electrons and ions. We find that the maximum growth rates tend to increase but reach steady states as the wave number increases. The instabilities reported here could be relevant to various plasma environments, including space plasmas (e.g., Earth's magnetosphere) and laboratory dusty plasma experiments.

physics.plasm-ph↗

arXiv2025

Thermoacoustic internal gravity wave turbulence in the Earth's lower atmosphere

We propose, for the first time, a two-dimensional model for the nonlinear coupling of internal gravity and thermal waves in the presence of temperature-dependent density inhomogeneity due to thermal expansion and thermal feedback in stratified fluids of the Earth's lower atmosphere ($0-50$ km). Such a coupling gives rise to the evolution of thermoacoustic internal gravity waves (IGWs), which are distinctive from the known IGWs in the literature. We perform numerical simulations to study the nonlinear interactions of velocity and density perturbations associated with the IGWs and thermal fluctuations corresponding to the thermal mode. We show that solitary vortices of IGWs coupled to the thermal wave can lead to thermoacoustic turbulence. We observe the formation of large-scale velocity potential flows and small-scale structures in the density and temperature profiles. Interestingly, while the wave energy spectra exhibit power laws: $ k_x^{-1.67}$ and $ k_z^{-2.89}$, respectively, for horizontal and vertical wave numbers, in the troposphere ($0-15$ km) with negative temperature gradient, the same in the stratosphere ($15-50$ km) with positive temperature gradient tend to relax toward $k_x^{-1.83}$-horizontal and $k_z^{-1.03}$-vertical spectra. We find that while the energy spectra in the tropospheric turbulence are consistent with the observed phenomena without temperature gradients, those in the stratosphere differ.

physics.ao-ph↗

arXiv2025

Dust-ion-acoustic solitons in an ion-beam-driven dusty magnetoplasma with adiabatic and nonadiabatic dust charge variations

We study the characteristics of small-amplitude nonlinear dust-ion-acoustic (DIA) solitary waves in active magnetized positive-ion-beam-driven dusty plasmas with the effects of nonadiabatic and adiabatic dust charge variations. In the model, we consider the ion-neutral collision and thereby consider the collision enhanced ion current to the dust-charging process and dust charge fluctuations. We show that the streaming of the positive-ion beam significantly affects the dust-charging process in which the dust charge number decreases (increases) with an increased beam velocity (number density). Using the standard reductive perturbation technique, we derive the evolution equations in the form of Korteweg-de Vries (KdV) equations for DIA solitary waves for two different cases: nonadiabatic and adiabatic dust charge variations. We study the effect of positive ion beam, dust charge variation, magnetic field, ion creation, and ion-neutral collision enhanced current on the wave characteristics. We find that the soliton energy decays with time and is affected by the beam velocity. Also, the solitary waves get damped by the effects of ion creation, ion loss, ion-neutral collision enhanced current, and dust charge variation. Although the ion beam does not change the polarity of solitary waves in the case of adiabatic dust charge variation, a transition from rarefactive to compressive solitary waves occurs in the presence of an ion beam with nonadiabatic dust charge variation.

physics.plasm-ph↗

arXiv2025

Coupling of Alfvén and magnetosonic waves in rotating Hall magnetoplasmas

We study the linear theory of magnetohydrodynamic (MHD) waves, namely the Alfv{é}n and the fast and slow magnetosonic modes in a rotating Hall-MHD plasma with the effects of the obliqueness of the external magnetic field and the Coriolis force and show that these waves can be coupled either by the influence of the Coriolis force or the Hall effects. To this end, we derive a general form of the linear dispersion relation for these coupled modes by the combined influence of the Coriolis force and the Hall effects and analyze numerically their characteristics in three different plasma-$β$ regimes: $β\sim1$, $β>1$, and $β<1$, including some particular cases. We show that while the coupling between the Alfv{é}n and the fast magnetosonic modes is strong in the low-$β$ $(β\lesssim1)$ regime and the wave dispersion appears in the form of a thumb curve, in the high-$β~(β>1)$ regime, the strong coupling can occur between the Alfv{é}n and the slow magnetosonic modes and the dispersion appears in the form of a teardrop curve. Switching of the coupling in the regime of $β\sim1$ can occur, i.e., instead of a thumb curve, a teardrop curve appears when the obliqueness of propagation and rotational angle are close to $70^\circ$ or more (but less than $90^\circ$). Implications of our results to solar and fusion plasmas are briefly discussed.

physics.plasm-ph↗

arXiv2025

Rayleigh-Bénard convective motion of stratified fluids in the Earth's troposphere

Recently, Kaladze and Misra [Phys. Scr. 99 (2024) 085013] showed that the tropospheric stratified fluid flows may be unstable by the effects of the negative temperature gradient and the temperature-dependent density inhomogeneity arising from the thermal expansion. They also predicted that the modification in the Brunt-V{ä}is{ä}l{ä} frequency by the density inhomogeneity can lead to Rayleigh-B{é}nard convective instability in the tropospheric unbounded layers. The purpose of the present work is to revisit the Rayleigh-B{é}nard convective instability in more detail by considering both unbounded and bounded tropospheric layers. Starting from a set of fluid equations for incompressible neutral fluids with temperature gradients and using the Boussinesq approximation, we derive the general dispersion relations for Rayleigh-B{é}nard convective waves in unbounded and bounded tropospheric domains and analyze them with some particular cases both analytically and numerically. We show that the conditions for instability in these two cases significantly differ. Furthermore, we obtain and analyze the critical values of the Raleigh numbers and the expressions for the instability growth rates of thermal waves in the two cases. In the case of the bounded region, we also derive the necessary boundary conditions and note that the vertical wave number is quantified, and the corresponding eigenvalue problem is well-set.

physics.flu-dyn↗

arXiv2024

Rayleigh-Taylor instability in inhomogeneous relativistic classical and degenerate electron-ion magnetoplasmas

We study the Rayleigh-Taylor instability (RTI) of electrostatic plane wave perturbations in compressible relativistic magnetoplasma fluids with thermal ions under gravity in three different cases of when (i) electrons are in isothermal equilibrium, i.e., classical or nondegenerate, (ii) electrons are fully degenerate (with $T_e=0$), and (iii) electrons are partially degenerate or have finite temperature degeneracy (with $T_e\neq0$). While in the cases of (i) and (iii), we focus on the regimes where the particle's thermal energy is more or less than the rest mass energy, i.e., $β_e \equiv k_{\mathrm B}T_e/{m_ec^2}<1~\rm{or}~>1$, the case (ii) considers from weakly to ultra-relativistic degenerate regimes. A general expression of the growth rate of instability is obtained and analyzed in the three different cases relevant to laboratory and astrophysical plasmas, which generalize and advance the previous theory on RTI.

physics.plasm-ph↗

arXiv2024

Transverse instability of electron-acoustic solitons in a relativistic degenerate astrophysical magnetoplasma

We study the nonlinear theory of small-amplitude electron-acoustic solitons (EASs) in a relativistic astrophysical magnetoplasma consisting of two-temperature electrons: a sparse population of relativistic nondegenerate classical electrons and a group of fully degenerate dense relativistic electrons (main constituent) immersed in a static magnetic field with a neutralizing stationary ion background. By using the multiple-scale reductive perturbation technique with the Lorentz transformation, the Zakharov-Kuznetsov (ZK) and the modified Zakharov-Kuznetsov (mZK) equations are derived to describe the evolution of EASs in two different regimes of relativistic degeneracy: $r_{d0}<50$ and $r_{d0}\gtrsim50$. The characteristics of the plane soliton solutions of ZK and mZK equations and the soliton energy are studied. We show that the solitons moving at an angle $α$ to the external magnetic field can be unstable under transverse long-wavelength perturbations. The growth rates of instabilities are obtained and analyzed with the effects of the relativity parameter $β_{\rm{cl}}=k_BT_{\rm{cl}}/m_ec^2$ and the degeneracy parameter $r_{d0}$, where $k_B$ is the Boltzmann constant and $T_{\rm{cl}}$ is the temperature of classical electrons. Interestingly, the ZK solitons, even if it is stable for the first-order perturbations, can be unstable in the second-order correction. Furthermore, while the first-order growth rates of perturbations for ZK solitons tend to vanish as $α\rightarrow 38^\circ$, that for the mZK soliton goes to zero as $α\rightarrow 90^\circ$. However, depending on the angle $α$, the growth rates are found to be reduced either by increasing the values of $β_{\rm{cl}}$ or by decreasing the values of $r_{d0}$. The applications of our results to astrophysical plasmas, such as those in the environments of white dwarfs are discussed.

physics.plasm-ph↗

arXiv2024

Analytical and numerical study of plane-progressive thermoacoustic shock waves in complex plasmas

The formation of thermoacoustic shocks is studied in a fluid complex plasma. The thermoacoustic wave mode can be damped (or anti-damped) when the contribution from the thermoacoustic interaction is lower (or higher) than that due to the particle collision and/or the kinematic viscosity. In the nonlinear regime, the thermoacoustic wave, propagating with the acoustic speed, can evolve into small amplitude shocks whose dynamics are governed by the Bateman-Burgers equation with an additional nonlinear term that appears due to the particle collision and nonreciprocal interactions of charged particles providing the thermal feedback. The appearance of such nonlinearity can cause the shock fronts to be stable (or unstable) depending on the collision frequency remains below (or above) a critical value and the thermal feedback is positive. The existence of different kinds of shocks and their characteristics are analyzed analytically and numerically with the system parameters that characterize the thermal feedback, thermal diffusion, heat capacity per fluid particle, the particle collision and the fluid viscosity. A good agreement between analytical and numerical results is also noticed.

physics.plasm-ph↗

arXiv2024

Ion-acoustic solitons in a relativistic Fermi plasma at finite temperature

The theory of ion-acoustic solitons in nonrelativistic fully degenerate plasmas and nonrelativistic and ultra-relativistic degenerate plasmas at low temperatures is known. We consider a multi-component relativistic degenerate electron-positron-ion plasma at finite temperatures. Specifically, we focus on the intermediate region where the particle's thermal energy $(k_BT)$ and the rest-mass energy $(mc^2)$ do not differ significantly, i.e., $k_BT\sim mc^2$. However, the Fermi energy $(k_BT_F)$ is larger than the thermal energy and the normalized chemical energy ($ξ=μ/k_BT$) is positive and finite. Two different parameter regimes with $β\equiv k_BT/mc^2<1$ and $β>1$, relevant for astrophysical plasmas, are defined, and the existence of small amplitude ion-acoustic solitons in these regimes are studied, including the critical cases where the known KdV (Korteweg-de Vries) theory fails. We show that while the solitons with both the positive (compressive) and negative (rarefactive) potentials coexist in the case of $β<1$, only compressive solitons can exist in the other regime $(β>1)$. Furthermore, while the rarefactive solitons within the parameter domains of $β$ and $ξ$ can evolve with increasing amplitude and hence increasing energy, the energy of compressive solitons reaches a steady state.

physics.plasm-ph↗

arXiv2024

Nonlinear modulation of dispersive fast magnetosonic waves in an inhomogeneous rotating solar low-$β$ magnetoplasma

We study the modulation of fast magnetosonic waves (MSWs) in rotating inhomogeneous low-$β$ magnetoplasmas with the effects of gravitation and the Coriolis force. By employing the standard multiple-scale reductive perturbation technique (RPT), we derive a nonlinear Schrödinger (NLS) equation that governs the evolution of slowly varying MSW envelopes. The fast MSW becomes dispersive by the effects of the Coriolis force in the fluid motion, and the magnetic field and density inhomogeneity effects favor the Jeans instability in self-gravitating plasmas in a larger domain of the wave number ($k$, below the Jeans critical wave number, $k_J$) than homogeneous plasmas. The relative influence of the Jeans frequency ($ω_J$, associated with the gravitational force) and the angular frequency ($Ω_0$, relating to the Coriolis force) on the Jeans carrier MSW mode and the modulational instability (MI) of the MSW envelope is studied. We show that the MSW envelope (corresponding to the unstable carrier Jeans mode with $ω_J>2Ω_0$ and $k 2Ω_0$ but $k>k_J$ manifests either modulational stability or MI having a finite growth rate before being cut off. We find an enhancement of the MI growth rate by the influence of magnetic field or density inhomogeneity. The case with constant gravity force (other than the self-gravity) perpendicular to the magnetic field is also briefly discussed to show that the fast magnetosonic carrier mode is always unstable, giving MI of slowly varying envelopes with no cut-offs for the growth rates. Possible applications of MI in solar plasmas, such as those in the X-ray corona, are also briefly discussed.

physics.plasm-ph↗

arXiv2024

Influence of temperature-dependent density inhomogeneity on the stability of atmospheric stratified fluids

The stability of atmospheric stratified fluids is revisited to study the influence of the temperature-dependent density inhomogeneity due to thermal expansion in the Earth's lower atmosphere (with heights $0$ to $50$ km) under the action of gravity. Previous theory in the literature [Phys. Lett. A 480 (2023) 128990] is modified and advanced. It is found that the Brunt-V{ä}is{ä}l{ä} frequency associated with internal gravity waves is modified, leading to new instability conditions of vertically stratified fluids. The possibility of the onset of Rayleigh-B{é}nard convective instability is also discussed, and the influences of the modified Brunt-V{ä}is{ä}l{ä} frequency and the density and temperature gradients on the instability growth rates are studied.

physics.ao-ph↗

arXiv2023

Thermal expansion of atmosphere and stability of vertically stratified fluids

The influence of the thermal expansion of the Earth's atmosphere on the stability of vertical stratification of fluid density and temperature is studied. We show that such an influence leads to the instability of incompressible flows. Modified by the thermal expansion coefficient, a new expression for the Brunt-V{ä}is{ä}l{ä} frequency is derived, and a critical value of the thermal expansion coefficient for which the instability occurs is revealed.

physics.ao-ph↗

arXiv2023

Modulation of electromagnetic waves in a relativistic degenerate plasma at finite temperature

We study the modulational instability (MI) of a linearly polarized electromagnetic (EM) wave envelope in an intermediate regime of relativistic degenerate plasmas at a finite temperature $(T\neq0)$ where the thermal energy $(K_BT)$ and the rest-mass energy $(m_ec^2)$ of electrons do not differ significantly, i.e., $β_e\equiv K_{B}T/m_{e}c^2\lesssim~(\rm{or}~\gtrsim) 1$, but, the Fermi energy $(K_BT_F)$ and the chemical potential energy $(μ_e)$ of electrons are still a bit higher than the thermal energy, i.e., $T_F>T$ and $ξ_{e}=μ_e/K_{B}T\gtrsim1$. Starting from a set of relativistic fluid equations for degenerate electrons at finite temperature, coupled to the EM wave equation and using the multiple scale perturbation expansion scheme, a one-dimensional nonlinear Sch{ö}dinger (NLS) equation is derived, which describes the evolution of slowly varying amplitudes of EM wave envelopes. Then we study the MI of the latter in two different regimes, namely $β_e<1$ and $β_e>1$. Like unmagnetized classical cold plasmas, the modulated EM envelope is always unstable in the region $β_e>4$. However, for $β_e\lesssim1$ and $1<β_e<4$, the wave can be stable or unstable depending on the values of the EM wave frequency, $ω$ and the parameter $ξ_e$. We also obtain the instability growth rate for the modulated wave and find a significant reduction by increasing the values of either $β_e$ or $ξ_e$. Finally, we present the profiles of the traveling EM waves in the form of bright (envelope pulses) and dark (voids) solitons, as well as the profiles (other than traveling waves) of the Kuznetsov-Ma breather, the Akhmediev breather, and the Peregrine solitons as EM rogue (freak) waves, and discuss their characteristics in the regimes of $β_e\lesssim1$ and $β_e>1$.

physics.plasm-ph↗

arXiv2023

Enhancing chaos in multistability regions of Duffing map for an asymmetric image encryption algorithm

This paper investigates and analyzes the dynamics of the two-dimensional Duffing map. Multistability behavior has been observed from the system numerically. Such behavior, especially the coexistence of chaotic and periodic attractors, is undesirable in the applications of chaos-based cryptography. Therefore, we design and implement a Sine-Cosine chaotification technique to enhance chaos in the multistable regions. Furthermore, this paper proposes a new image encryption algorithm to examine the performance of the generalized Duffing map in cryptography applications. Simulation results and security analysis reveal that the proposed algorithm can effectively encrypt and decrypt several image types with a high level of security.

nlin.PS↗

arXiv2023

Neutrino magnetohydrodynamic instabilities in presence of two-flavor oscillations

The influence of neutrino flavor oscillations on the propagation of magnetohydrodynamic (MHD) waves and instabilities is studied in neutrino-beam driven magnetoplasmas. Using the neutrino MHD model, a general dispersion relation is derived which manifests the resonant interactions of MHD waves, not only with the neutrino beam, but also with the neutrino flavor oscillations. It is found that the latter contribute to the wave dispersion and enhance the magnitude of the instability of oblique magnetosonic waves. However, the shear-Alfv{é}n wave remains unaffected by the neutrino beam and neutrino flavor oscillations. Such an enhancement of the magnitude of the instability of magnetosonic waves can be significant for relatively long-wavelength perturbations in the regimes of high neutrino number density and/or strong magnetic field, giving a convincing mechanism for type-II core-collapse supernova explosion.

physics.plasm-ph↗