scholarly journals Nonlinear low-frequency wave aspect of foreshock density holes

2008 ◽  
Vol 26 (12) ◽  
pp. 3707-3718 ◽  
Author(s):  
N. Lin ◽  
E. Lee ◽  
F. Mozer ◽  
G. K. Parks ◽  
M. Wilber ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Plane Electromagnetic Wave ◽  
Timing Analysis ◽  
Low Frequency ◽  
Resonant Interaction ◽  
Ion Temperature ◽  
Temperature Anisotropy ◽  
Frequency Wave ◽  
Wave Nature ◽  
The Waves

Abstract. Recent observations have uncovered short-duration density holes in the Earth's foreshock region. There is evidence that the formation of density holes involves non-linear growth of fluctuations in the magnetic field and plasma density, which results in shock-like boundaries followed by a decrease in both density and magnetic field. In this study we examine in detail a few such events focusing on their low frequency wave characteristics. The propagation properties of the waves are studied using Cluster's four point observations. We found that while these density hole-structures were convected with the solar wind, in the plasma rest frame they propagated obliquely and mostly sunward. The wave amplitude grows non-linearly in the process, and the waves are circularly or elliptically polarized in the left hand sense. The phase velocities calculated from four spacecraft timing analysis are compared with the velocity estimated from δE/δB. Their agreement justifies the plane electromagnetic wave nature of the structures. Plasma conditions are found to favor firehose instabilities. Oblique Alfvén firehose instability is suggested as a possible energy source for the wave growth. Resonant interaction between ions at certain energy and the waves could reduce the ion temperature anisotropy and thus the free energy, thereby playing a stabilizing role.

scholarly journals Geomagnetic activity and local time dependence of the distribution of ultra low-frequency wave power in azimuthal wavenumbers, <i>m</i>

2017 ◽  
Vol 35 (3) ◽  
pp. 629-638 ◽  
Author(s):  
Theodore E. Sarris ◽  
Xinlin Li
Keyword(s):  
Phase Difference ◽  
Low Frequency ◽  
Field Measurements ◽  
Resonant Interaction ◽  
Total Power ◽  
Ulf Waves ◽  
Quiet Time ◽  
Frequency Wave ◽  
Drift Frequency ◽  
Diffusion Rates

Abstract. The azimuthal wavenumber m of ultra low-frequency (ULF) waves in the magnetosphere is a required parameter in the calculations of the diffusion rates of energetic electrons and protons in the magnetosphere, as electrons and protons of drift frequency ωd have been shown to radially diffuse due to resonant interaction with ULF waves of frequency ω = mωd. However, there are difficulties in estimating m, due to lack of multipoint measurements. In this paper we use magnetic field measurements at geosynchronous orbit to calculate the cross-spectrogram power and phase differences between time series from magnetometer pairs. Subsequently, assuming that ULF waves of a certain frequency and m would be observed with a certain phase difference between two azimuthally aligned magnetometers, the fraction of the total power in each phase difference range is calculated. As part of the analysis, both quiet-time and storm-time distributions of power per m number are calculated, and it is shown that during active times, a smaller fraction of total power is confined to lower m than during quiet times. It is also shown that in the dayside region, power is distributed mostly to the lowest azimuthal wavenumbers m = 1 and 2, whereas on the nightside it is more equally distributed to all m that can be resolved by the azimuthal separation between two spacecraft.

Helicity waves propagating in a plasma

1991 ◽  
Vol 45 (3) ◽  
pp. 481-488 ◽  
Author(s):  
Z. Yoshida
Keyword(s):  
Magnetic Field ◽  
Faraday Effect ◽  
Low Frequency ◽  
Plasma Waves ◽  
Frequency Limit ◽  
High Frequencies ◽  
Transverse Modes ◽  
Longitudinal Part ◽  
The Waves ◽  
Perturbed Magnetic Field

There exist plasma waves that transport helicity although they do not propagate electromagnetic energy. The dispersion relations of such helicity waves are studied. The electric field of the waves is parallel to the perturbed magnetic field, and both are perpendicular to the perturbed current. In cross-field propagation, a helicity wave is decomposed into two transverse modes with different polarizations and a longitudinal part. The helicity waves are principally Alfvénic in the low-frequency limit. At high frequencies, the Faraday effect comes into the polarization.

scholarly journals On a nonlinear state of the electromagnetic ion/ion cyclotron instability

2000 ◽  
Vol 7 (3/4) ◽  
pp. 173-177
Author(s):  
M. Cremer ◽  
M. Scholer
Keyword(s):  
Magnetic Field ◽  
Boundary Layer ◽  
Plasma Sheet ◽  
Large Temperature ◽  
Plasma Sheet Boundary Layer ◽  
Temperature Anisotropy ◽  
Nonlinear Properties ◽  
Cyclotron Instability ◽  
Ion Cyclotron ◽  
The Waves

Abstract. We have investigated the nonlinear properties of the electromagnetic ion/ion cyclotron instability (EMIIC) by means of hybrid simulations (macroparticle ions, massless electron fluid). The instability is driven by the relative (super-Alfvénic) streaming of two field-aligned ion beams in a low beta plasma (ion thermal pressure to magnetic field pressure) and may be of importance in the plasma sheet boundary layer. As shown in previously reported simulations the waves propagate obliquely to the magnetic field and heat the ions in the perpendicular direction as the relative beam velocity decreases. By running the simulation to large times it can be shown that the large temperature anisotropy leads to the ion cyclotron instability (IC) with parallel propagating Alfvén ion cyclotron waves. This is confirmed by numerically solving the electromagnetic dispersion relation. An application of this property to the plasma sheet boundary layer is discussed.

scholarly journals Polar spacecraft observations of the turbulent outer cusp/magnetopause boundary layer of Earth

1999 ◽  
Vol 6 (3/4) ◽  
pp. 195-204 ◽  
Author(s):  
J. S. Pickett ◽  
J. D. Menietti ◽  
J. H. Dowell ◽  
D. A. Gurnett ◽  
J. D. Scudder
Keyword(s):  
Magnetic Field ◽  
Index Of Refraction ◽  
Local Magnetic Field ◽  
Lower Hybrid ◽  
Frequency Wave ◽  
Turbulent Region ◽  
Wave Data ◽  
Field Environment ◽  
Whistler Mode Waves ◽  
The Waves

Abstract. The orbit of the Polar spacecraft has been ideally suited for studying the turbulent region of the cusp that is located near or just outside the magnetopause current sheet at 7-9 RE. The wave data obtained in this region show that electromagnetic turbulence is dominant in the frequency range 1-10 Hz. The waves responsible for this turbulence usually propagate perpendicular to the local magnetic field and have an index of refraction that generally falls between the estimated cold plasma theoretical values of the electromagnetic lower hybrid and whistler modes and may be composed of both modes in concert with kinetic Alfvén waves and/or fast magnetosonic waves. Fourier spectra of the higher frequency wave data also show the electromagnetic turbulence at frequencies up to and near the electron cyclotron frequency. This higher frequency electromagnetic turbulence is most likely associated with whistler mode waves. The lower hybrid drift and current gradient instabilities are suggested as possible mechanisms for producing the turbulence. The plasma and field environment of this turbulent region is examined and found to be extremely complex. Some of the wave activity is associated with processes occurring locally, such as changes in the DC magnetic field, while others are associated with solar wind and interplanetary magnetic field changes.

Comparison of different techniques to estimate the direction of the Poynting vector of EMIC emissions

2021 ◽  
Author(s):  
Benjamin Grison ◽  
Ondrej Santolik
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Poynting Vector ◽  
Source Region ◽  
Transverse Component ◽  
Equatorial Region ◽  
Magnetic Equator ◽  
Ion Temperature ◽  
Temperature Anisotropy ◽  
Single Plane

&lt;p&gt;Electromagnetic Ion Cyclotron (EMIC) waves usually grow in the inner magnetosphere from hot ion temperature anisotropy. The main source region is located close to the magnetic equator and there is a secondary EMIC source region off the magnetic equator in the dayside magnetosphere. The source region can be identified using measurements of the Poynting vector direction.&lt;/p&gt;&lt;p&gt;The Poynting vector is ideally derived from the measurement of 3 components of the wave electric field and 3 components of components of the wave magnetic field. However, spinning spacecraft often have only two long mutually perpendicular electric antennas in the spin plane, deployed by the centrifugal force. The third antenna, when present, is usually shorter owing to difficulties of deploying a antenna along the spin axis.&lt;/p&gt;&lt;p&gt;Estimations of the Poynting vector from measurements of three magnetic field components and two electric field components can be obtained assuming the presence of a single plane wave (and thus perpendicularity of the electric field and the magnetic field vectors, according to the Faraday&amp;#8217;s law), following the method developed by Loto'aniu et al. (2005). Applying this method to Cluster data, Allen et al. (2013) found the presence of bidirectional EMIC emissions off the magnetic equatorial region.&lt;/p&gt;&lt;p&gt;Another technique proposed earlier by Santol&amp;#237;k et al. (2001) considers the phase shift estimation between the electric signals from each antenna and synthetic perpendicular magnetic field components obtained from the three-dimensional measurements. The method is based on cross-spectral estimates in the frequency domain and can be used to estimate sign of each component of the Poynting vector. Using this technique Grison et al. (2016) showed the importance of the transverse component of the EMIC emissions far from the source region.&lt;/p&gt;&lt;p&gt;We compare these methods for different events to check how the results of these two techniques differ. We also discuss what we can learn about the EMIC source region from these measurements.&lt;/p&gt;

Whistler radiation in plasmas with cylindrical magnetic field irregularities

2009 ◽  
Vol 76 (2) ◽  
pp. 193-207 ◽  
Author(s):  
C. KRAFFT ◽  
T. M. ZABORONKOVA
Keyword(s):  
Magnetic Field ◽  
Laboratory Experiments ◽  
Low Frequency ◽  
Wave Radiation ◽  
Whistler Waves ◽  
Frequency Wave ◽  
Ambient Magnetic Field ◽  
Physical Conditions ◽  
Local Perturbations ◽  
Dipole Sources

AbstractThe radiation of whistler waves by linear dipole sources immersed in magnetoplasmas with cylindrical magnetic field inhomogeneities are studied. Two types of irregularities are investigated: magnetic field enhancements and depletions. A theoretical analysis is developed for comparatively weak local perturbations of the ambient magnetic field. Results are provided by numerical calculations performed for physical conditions typical of laboratory experiments involving artificially created magnetic field irregularities. It is shown that plasma regions with locally enhanced (depleted) magnetic field intensities can increase (decrease) the amplitudes of whistler waves radiated by dipole sources, regardless of their orientation with respect to the ambient magnetic field. Results are relevant to space and laboratory experiments on very low-frequency wave radiation.

Statistical occurrence of mirror mode waves at Mars

2020 ◽  
Author(s):  
Cyril Simon Wedlund ◽  
Martin Volwerk ◽  
Christian Mazelle ◽  
Christian Möstl ◽  
Diana Rojas-Castillo ◽  
...  
Keyword(s):  
Solar Cycle ◽  
High Plasma ◽  
Bow Shock ◽  
Ion Temperature ◽  
Temperature Anisotropy ◽  
Frequency Wave ◽  
Solar Cycle 24 ◽  
Mirror Mode ◽  
Cycle 24 ◽  
Mm Waves

&lt;p&gt;Ultra low-frequency wave activity such as mirror mode (MM) waves, arising from an ion temperature anisotropy in the plasma, has been ubiquitously detected in the magnetosheaths of Venus and Mars. The MM instability is usually triggered behind a quasi-perpendicular bow shock in a high plasma &amp;#946;. We present here a statistical survey of these waves at Mars using magnetometer and ion data from the NASA/MAVEN mission between 2014 and 2019 (solar cycle 24, receding activity). First, quasi-perpendicular bow shock crossings are identified in the data using simple bow shock models (Edberg et al. 2008, Gruesbeck et al. 2018, Hall et al. 2019). MM waves are then automatically detected for these conditions, first from magnetometer measurements only (in the manner of Volwerk et al., 2016), and second using both magnetometer and ion moments to refine the analysis. Maps of MM wave occurrence for solar cycle 24 are presented and preliminary comparisons with similar and different solar activity conditions with MGS and Mars Express data are discussed.&lt;/p&gt;

The inhomogeneous ion temperature anisotropy instabilities of magnetic-field-aligned plasma sheared flow

2016 ◽  
Vol 23 (11) ◽  
pp. 112122 ◽  
Author(s):  
V. V. Mikhailenko ◽  
V. S. Mikhailenko ◽  
Hae June Lee
Keyword(s):  
Magnetic Field ◽  
Ion Temperature ◽  
Temperature Anisotropy ◽  
Sheared Flow

scholarly journals Reconnection in Pulsar Winds

2001 ◽  
Vol 18 (4) ◽  
pp. 415-420 ◽  
Author(s):  
J. G. Kirk ◽  
Y. Lyubarsky
Keyword(s):  
Magnetic Field ◽  
Energy Transport ◽  
Crab Nebula ◽  
Low Frequency ◽  
Frequency Wave ◽  
Poynting Flux ◽  
High Particle ◽  
The Crab Nebula ◽  
Pulsar Winds ◽  
The Magnetic Field

AbstractThe spin-down power of a pulsar is thought to be carried away in an MHD wind in which, at least close to the star, the energy transport is dominated by Poynting flux. The pulsar drives a low frequency wave in this wind, consisting of stripes of toroidal magnetic field of alternating polarity, propagating in a region around the equatorial plane. The current implied by this configuration falls off more slowly with radius than the number of charged particles available to carry it, so that the MHD picture must, at some point, fail. Recently, magnetic reconnection in such a structure has been shown to accelerate the wind significantly. This reduces the magnetic field in the comoving frame and, consequently, the required current, enabling the solution to extend to much larger radius. This scenario is discussed and, for the Crab Nebula, the range of validity of the MHD solution is compared with the radius at which the flow appears to terminate. For sufficiently high particle densities, it is shown that a low frequency entropy wave can propagate out to the termination point. In this case, the ‘termination shock’ itself must be responsible for dissipating the wave.This paper is dedicated to Don Melrose on his 60th birthday.

scholarly journals ACCELERATION OF PARTICLES BY INTENSIVE ELECTROMAGNETIC FIELDS IN A VACUUM WITH EXTERNAL MAGNETIC FIELD

2020 ◽  
pp. 73-77
Author(s):  
V.А. Buts ◽  
V.V. Kuzmin ◽  
A.P. Tolstoluzhsky
Keyword(s):  
Magnetic Field ◽  
Particle Acceleration ◽  
External Magnetic Field ◽  
Plane Electromagnetic Wave ◽  
Effective Interaction ◽  
Charged Particles ◽  
Resonant Interaction ◽  
Acceleration Of Particles ◽  
Effective Particle ◽  
Small Wave

The possibilities and conditions of effective interaction, in particular acceleration, of charged particles by the field of an intense plane electromagnetic wave in the presence of an external constant magnetic field are considered. It is shown that the well-known conditions of cyclotron resonances require generalization. New conditions for the resonant interaction of charged particles are formulated, which contain not only the strength of the external magnetic field (as the well-known conditions of cyclotron resonances) but also the field strength of the wave. Cases of both small wave field strengths, so large, are considered. It is shown that new resonance conditions open up new possibilities for effective particle acceleration.

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