Hydromagnetic waves driven by velocity shear instability in the magnetospheric boundary layer

The bulk flow of the solar wind plasma in the flank-side of the magnetospheric boundary layer, where the magnetic field lines are closed, has a component transverse to the ambient field. There is quite a strong velocity shear. The theoretical model ignores inhomogeneities in the ambient field and the mass density which occur at the magnetopause on about the same length scale as that of the velocity shear.Consideration is restricted to hydromagnetic waves which have a k-vector nearly normal to the B_o-V_o plane, i.e., approximately the magnetopause surface (k_x >k_z ～ k_y′k_xL_B > 1 and L_B = 0.1 ～ 1.0 R_E where L_B is a characteristic length of the boundary layer). It is found that a long-period (T ? 40 sec) hydromagnetic wave [the Alfvén-like wave ($\text{Ω}{}_{\mathrm{<mtext>A</mtext>}}$)] driven by velocity shear instability can be excited in the shear plasma. It is also found that the group velocity of the HM-wave is directed almost along the magnetic field line and that the magnetic variance in the shear plasma tends to be parallel to the B_o-V_o plane. The velocity shear instability in the magnetospheric boundary layer is judged to be a likely source of long-period magnetic pulsations.     

Dynamics of the earth radiation belts during strong magnetic storms based on <Emphasis Type="Italic">CORONAS-F</Emphasis> data

The results of an experimental study of the variations in the intensity of the fluxes of the Earth radiation belt (ERB) particles in 0.3–6 and 1–50 MeV energy intervals for electrons and protons, respectively, are reported. ERBs were studied during strong magnetic storms from August 2001 through November 2003. The results of the CORONAS-F mission obtained during the magnetic storms of November 6 (D _st = ?257 nT) and November 24, 2001 (D _st = ?221 nT), October 29–30 (D _st = ?400 nT) and November 20, 2003 (D _st = ?465 nT) are analyzed. The electron flux is found to decrease abruptly in the outer radiation belt during the main phase of the magnetic storms under consideration. During the recovery phase, the outer radiation belt is found to recover much closer to Earth, near the boundary of the penetration of solar electrons during the main phase of the magnetic storm. We associate the decrease in the electron flux with the abrupt decrease of the size of the magnetosphere during the main phase of the storm. Note that, in all cases studied, the Earth radiation belts exhibited rather long (several days) variations. In those cases where solar cosmic-ray fluxes were observed during the storm, protons with energies 1–5 MeV could be trapped to form an additional maximum of protons with such energies at L >2.     

Formation of proton fluxes under the radiation belts during geomagnetic disturbances

The fluxes of energetic particles under the radiation belts are studied using data obtained in the experiments onboard the CORONAS-I and CORONAS-F satelites. The spatial structure of the distributions of proton fluxes with E _p > 1 MeV both near the geomagnetic equator on L ≤ 1.2 and at high latitudes on L ～ 3.5–6.5 as well as the particle flux variations with geomagnetic activity are analyzed. The scattering processes that lead to particle precipitation and, in particular, the scattering of protons as they interact with VLF emission and the scattering when the particle motion becomes nonadiabatic are considered. We compare the data on particle dynamics during geomagnetic disturbances of various kinds to determine whether the physical processes that lead to particle precipitation are a manifestation of the geoefficiency of a given magnetic storm or they are controlled by internal magnetospheric conditions.     

Effects of magnetospheric turbulence on electron plasma waves

Our calculations indicate that high frequency plasma waves can be efficiently generated by electrostatic turbulence in the magnetosphere.     

On the spatial structure and dispersion of slow magnetosonic modes coupled with Alfvén modes in planetary magnetospheres due to field line curvature

The structure of the slow mode coupled with Alfvén mode in the axially symmetric magnetosphere is studied in the paper. Due to the coupling, the slow magnetosonic wave gets dispersion across magnetic shells and becomes not strictly guided. The slow mode is found to be captured between the resonant and cutoff surfaces, where the wave vector radial component goes to infinity and to zero, accordingly. The resonant surface is farther from the Earth than the cutoff surface. The slow mode resonance frequency is much lower than the Alfvén resonance frequency due to small value of the sound velocity near the equator. The maximum of the slow mode amplitude expressed in terms of the parallel magnetic field is concentrated near the equator, but expressed in hydromagnetic terms is concentrated near the ionospheres.     

Comment on the group velocity of surface waves on the plasma sheet boundary

In the recent estimation by Maltsev and Lyatsky (1984) of the group velocity of surface waves on the inner boundary of the plasma sheet, the effect of the curvature of the field lines of the ambient magnetic field of the Earth on the spectrum has been assessed. The authors have not accounted for the fact, however, that the group velocity of the compressional surface magnetohydrodynamic waves itself is nonzero transverse to the magnetic field—a characteristic which has been omitted in the spectrum of Chen and Hasegawa (1974), being used by Maltsev and Lyatsky.This characteristic of compressional surface MHD waves is inherent for the spectrum $\text{ω = (}\text{k}{}_6\text{k}\text{)V}{}_{\mathrm{A}}\text{(k}{}^2{}_6\text{+ 2k}{}^2{}_{\mathrm{\perp }}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, obtained by Nenovski (1978) in the cold plasma limit V_A ? V_S(V_A is Alfvén velocity, and V_S, sound velocity). A comment has been made on the restrictions, proceeding from the approximation, used by Maltsev and Lyatsky. The estimation of the velocities for movements of auroral riometer absorption bays have been reviewed.     

The effect of non-uniform ionospheric conductivity on standing magnetospheric Alfven waves

We look at time-dependent normal mode solutions to the Alfven wave equation in a uniform magnetic field, between planar ionospheres. In particular, the effect of sharp gradients in ionospheric conductivity on the spatial and temporal structure of the waves is considered. We show that the electric field of the wave must always be perpendicular to any conductivity discontinuities present, and that this is achieved by the generation of circularly polarized Alfven waves at the discontinuity. The results are applied to an ionospheric strip of high conductivity; this being relevant to Pi2s.     

Surface waves on the plasma sheet boundary

A dispersion equation for the surface waves on the inner boundary of the magnetospheric plasma sheet is obtained. The wave group velocity has both components along and across the magnetic field. For the waves with the period 1 min the transverse component is about 100 km s⁻¹, the parallel component is approximately equal to the Alfvén velocity. Pi2 pulsations, as well as east-westward motions of auroral riometer absorption bays, may be possible displays of surface waves.     

The mechanism of magnetospheric substorm and the MHD waves of the solar wind

A mechanism of the Earth's magnetospheric substorm is proposed. It is suggested that the MHD waves may propagate across the magnetopause from the magnetosheath into the magnetotail and will be dissipated in the plasma sheet, heating the plasma and accelerating the particles. When the solar wind parameters change, the Poynting flux of the waves transferred from the magnetosheath into the tail, may be greater than 10¹⁸ erg s^?1. The heated plasma and accelerated particles in the plasma sheet will be injected into the inner magnetosphere, and this may explain the process of the ring current formation and auroral substorm.The Alfvén wave can only propagate along the magnetic force line into the magnetosphere in the open magnetosphere, but the magnetosonic wave can propagate in both the open and closed magnetosphere. When the IMF turns southward, the configuration of the magnetosphere will change from a nearly closed model into some kind of open one. The energy flux of Alfvén waves is generally larger than that of the magnetosonic wave. This implies that it is easy to produce substorms when the interplanetary magnetic field (IMF) has a large southward component, but the substorm can also be produced even if the IMF is directed northward.     

On the effect of oblique disturbances on Kelvin-Helmholtz instability at magnetospheric boundary layers and in solar wind

This paper is concerned with the Kelvin-Helmholtz instability in the indissipative plasma with an external magnetic field. A detailed analysis is made of the results known from the approximation of a tangential discontinuity. The finiteness of the interface thickness effect is considered numerically at the arbitrary distribution of the density, velocity and magnetic field vectors inside this shear layer. The influence of plasma compressibility with an arbitrarily varying magnetic field is investigated. The main role of oblique disturbances with respect to the flow rate direction is shown under conditions of a large plasma compressibility. As such perturbations move away from the interface, their amplitude is damped much more slowly than in the case of weak compressibility. However, their wavelength remains, approximately, the same as that of longitudinal waves in the case of incompressibility. The linear approximation suggests the importance of oblique waves in the energetics of the interaction between the shear layer and the outward medium. A comparison is made of the instability period on discontinuities in the solar wind, and at magnetospheric and plasmaspheric boundaries, with the range of geomagnetic pulsations.     

Effect of parallel electric fields on whistler mode waves in an anisotropic Jovian magnetospheric plasma

The effect of parallel electrostatic field on the amplification of whistler mode waves in an anisotropic bi-Maxwellian weakly ionized plasma for Jovian magnetospheric conditions has been carried out. The growth rate for different Jovian magnetospheric plasma parameters forL = 5.6R _j has been computed with the help of general dispersion relation for the whistler mode electromagnetic wave of a drifted bi-Maxwellian distribution function. It is observed that the growth or damping of whistler mode waves in Jovian magnetosphere is possible when the wave vector is parallel or antiparallel to the static magnetic field and the effect of this field is more pronounced at low frequency wave spectrum.     

Identification of the ionospheric footprint of magnetospheric boundaries using SuperDARN coherent HF radars

Several studies of SuperDARN radar data have revealed a systematic dependence of the Doppler backscatter versus latitude and magnetic local time. In particular, the Doppler spectral width is known to increase at the vicinity of the ionospheric footprint of the cusp, and in a region that shapes like the poleward boundary of the auroral oval. Following earlier work, we make use of a large radar database consisting of a set of key parameters that characterize Doppler backscatter, and a multivariate statistical method, to reveal a strong connection between specific geophysical regions and their backscatter properties. This opens the interesting perspective of monitoring magnetospheric boundaries in real time.     

Kinetic Alfven waves in plasma sheet boundary layer—particle aspect analysis

The particle aspect approach is adopted to investigate the trajectories of charged particles in the electromagnetic field of kinetic Alfven wave. Expressions are found for the dispersion relation, damping rate and associated currents in homogenous plasma. Kinetic effects of electrons and ions are included to study kinetic Alfven wave because both are important in the transition region. It is found that the ratio β of electron thermal energy density to magnetic field energy density and the ratio of ion to electron thermal temperature (T_i/T_e) affect the dispersion relation, damping-rate and associated currents in both cases (warm and cold electron limits). The treatment of kinetic Alfven wave instability is based on the assumption that the plasma consists of resonant and non-resonant particles. The resonant particles participate in an energy exchange process, whereas the non-resonant particles support the oscillatory motion of the wave.     

Spiral density waves illustrated by the superposition of periodic stellar orbits

Plane, periodic stellar orbits in the spiral gravitational field of the Galaxy superimposed on the axisymmetric background potential are studied in the epicyclic approximation. The superposition of such orbits is illustrated to demonstrate the response of the stellar system to an imposed spiral density perturbation.     

On the properties of magnetoacoustic surface waves

The nature of magnetoacoustic surface waves at a single magnetic interface, one side of which is field-free, is explored for the case of parallel propagation. The interface may support a slow surface wave or both slow and fast surface waves, depending upon the ordering of the sound speeds in the two media. Phase-speeds and penetration depths of the waves and the associated pressure perturbations and motions are investigated for a variety of field strengths and sound speeds. The fast wave disturbs the interface more than the slow wave. In the magnetic field region the slow wave is mainly longitudinal in nature whilst the fast surface wave is transverse for strong fields, longitudinal for weaker fields. In the field-free region both waves are longitudinal in character. The running penumbral wave phenomenon may provide an example of a magnetoacoustic surface mode, though any direct comparison requires the inclusion of gravitational effects.     

Nonlinear standing waves on the surface of a self-gravitating cylinder

The weakly nonlinear standing waves on the surface of a self-gravitating incompressible fluid column are investigated in the presence of, a uniform axial-magnetic field. By use of the method of multiple scales, we have shown that near the critical wave number, the amplitude modulation of a standing wave can be described by a nonlinear Schrödinger equation with the roles of time and space variable interchanged. It is demonstrated that in presence of a magnetic field, the system is always stable near the critical wave number.Department of Chemical Engineering, and TechnologyDepartment of Mathematics     

Effect of finite parallel conductivity on the magnetospheric convection

The magnetospheric plasma convection is studied, taking into account the finite conductivity along magnetic field lines. Field-aligned currents flowing at the inner boundary of the magnetospheric plasma sheet give rise to parallel electric fields which insignificantly affect the convection on the ionospheric level but change drastically the convection system in the magnetosphere. Intense azimuthal convective streams arise along both sides of the plasma sheet boundary. A part of convection lines appears to be completely closed in the inner magnetosphere.     

Nonlinear dispersive waves on the surface of a self-gravitating fluid layer

The evolution of two dimensional wave packets on the surface of a self-gravitating fluid layer is investigated and shown to be governed by a nonlinear Schrödinger equation. The wave train of finite amplitude is modulationally unstable. Obtained also are the dynamical equations for the second harmonic resonance. The analysis reveals that the general motion consists of both amplitude and phase modulated waves of which the pure phase and amplitude modulated waves, solitary waves, and phase jump are just the special cases.