Relativistic turning acceleration of resonant electrons by coherent whistler mode waves in a dipole magnetic field

2007 ◽  
Vol 112 (A6) ◽  
pp. n/a-n/a ◽  
Author(s):  
Yoshiharu Omura ◽  
Naoki Furuya ◽  
Danny Summers
Keyword(s):  
Magnetic Field ◽  
Whistler Mode ◽  
Dipole Magnetic Field ◽  
Whistler Mode Waves

Electron whistler mode instability in an inhomogeneous thermal plasma in the presence of an inhomogeneous beam of suprathermal electrons

1983 ◽  
Vol 29 (3) ◽  
pp. 439-448 ◽  
Author(s):  
H.A. Shah ◽  
V.K. Jain
Keyword(s):  
Magnetic Field ◽  
Growth Rate ◽  
Dispersion Relation ◽  
Thermal Plasma ◽  
Uniform Magnetic Field ◽  
Inhomogeneous Plasma ◽  
Mode Instability ◽  
Whistler Mode ◽  
Suprathermal Electrons ◽  
Whistler Mode Waves

The excitation of the whistler mode waves propagating obliquely to the constant and uniform magnetic field in a warm and inhomogeneous plasma in the presence of an inhomogeneous beam of suprathermal electrons is studied. The full dispersion relation including electromagnetic effects is derived. In the electrostatic limit the expression for the growth rate is given. It is found that the inhomogeneities in both beam and plasma number densities affect the growth rates of the instabilities.

Whistler-mode polarization in a hot anisotropic plasma

1985 ◽  
Vol 34 (2) ◽  
pp. 213-226 ◽  
Author(s):  
S. S. Sazhin
Keyword(s):  
Magnetic Field ◽  
Thermal Motion ◽  
Anisotropic Plasma ◽  
Whistler Mode ◽  
Electrostatic Waves ◽  
Electric And Magnetic Fields ◽  
Propagating Waves ◽  
Whistler Mode Waves ◽  
Electric Field Polarization ◽  
The Magnetic Field

Polarization of whistler-mode waves in a hot anisotropic plasma is considered in the two limiting cases of quasi-longitudinal and quasi-electrostatic propagation. It is pointed out that electron thermal motion never influences the phase of the propagating waves; the polarization of whistler-mode waves propagating along the magnetic field is totally independent of electron thermal motion. The deformation of polarization (in both electric and magnetic fields), of obliquely propagating whistler-mode waves could be, in principle, observed in magnetospheric conditions and thus could be used to estimate electron temperature and anisotropy. This deformation seems to be especially pronounced for the electric field polarization of quasi-electrostatic waves.

The Strength of Lightning on Venus Inferred from Ionospheric Whistler-Mode Waves

2020 ◽  
Author(s):  
Richard Hart ◽  
Christopher Russell ◽  
Jayesh Pabari ◽  
Tielong Zhang
Keyword(s):  
Magnetic Field ◽  
Phase Velocity ◽  
Solar Minimum ◽  
Solar Maximum ◽  
Polar Orbit ◽  
Whistler Mode ◽  
Poynting Flux ◽  
Whistler Mode Waves ◽  
Field Lines ◽  
The Waves

<p>Lightning produces an extremely low frequency (ELF) radio wave that propagates along magnetic field lines to higher altitudes in the ionosphere. Venus lacks an intrinsic magnetic dipole, so the interplanetary magnetic field (IMF) drapes around the planet forming a comet-like tail. The IMF induces currents in the ionosphere that generate an opposing field. The field lines tend to be nearly horizontal to the surface around much of the planet, except in the tail where it is more radial. There must be a dip to the field in order for waves to be guided to higher altitudes on the dayside. Therefore, a wave on the dayside is less likely to enter the ionosphere at the zenith of its source and more likely to enter at angles towards the horizon, where the field lines and wave path are more aligned.</p> <p>The dual fluxgate magnetometer onboard Venus Express (VEX) was able to detect ELF signals up to 64 Hz at various altitudes throughout the mission. We searched all available data within the ionosphere for lightning-generated whistler-mode waves. These waves are right-handed, circularly-polarized waves and propagate along the magnetic field. With a complete set of whistler observations, we can then calculate the Poynting flux of the waves. The Poynting flux requires the three components of both the wave electric field and magnetic field. Unfortunately, VEX did not have a means of measuring the electric field, but we can infer it if we know the phase velocity of the wave. In order to calculate the phase velocity, we need to employ the Venus International Reference Atmosphere model of electron density since VEX did not have any measurements coincident with whistler observations .</p> <p>The mission was in orbit from 2006-2014 and in that time there were nearly 7 cumulative hours of whistler observations below 400 km. In some cases, there was continuous activity for over a minute, implying a connection to an electrical storm below. These signals were most frequently seen when the spacecraft was at ~250 km altitude. Most signals were observed within 200-350 km altitude with a rate of ~3% of the time the spacecraft spent at these altitudes. It should be noted that due to the polar orbit of Venus Express, the lowest latitude of a detection was ~50°.</p> <p>The VEX mission spanned almost one solar cycle, so we can compare observations during the solar minimum and maximum periods. Because the ionosphere becomes strongly magnetized during solar minimum, detection rates are about twice as high compared to solar maximum. The Poynting flux during solar maximum shows a decrease with increasing altitude, providing further evidence that the waves were generated below the ionosphere. This conclusion is less clear during solar minimum. A large sample of case studies are left for future work to highlight features that might be lost to statistical averaging.</p> <p>Pioneer Venus (PVO) was able to detect the electric component of lightning-generated waves at 100 and 700 Hz, but on the nightside and at lower latitudes in contrast to the North polar orbit of VEX. The improved capability of VEX over PVO has greatly increased our knowledge of Venus lightning. The Indian Space Agency (IRSO) has announced plans for a future Venus orbiter at low latitudes. If a lightning oriented investigation were included, their data would be very complementary to previous studies.</p>

scholarly journals Quasi-parallel whistler mode waves observed by THEMIS during near-earth dipolarizations

2009 ◽  
Vol 27 (6) ◽  
pp. 2259-2275 ◽  
Author(s):  
O. Le Contel ◽  
A. Roux ◽  
C. Jacquey ◽  
P. Robert ◽  
M. Berthomier ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Electron Temperature ◽  
Linear Theory ◽  
Broad Band ◽  
Temperature Anisotropy ◽  
Whistler Mode ◽  
Background Magnetic Field ◽  
Whistler Mode Waves ◽  
Liouville’S Theorem

Abstract. We report on quasi-parallel whistler emissions detected by the near-earth satellites of the THEMIS mission before, during, and after local dipolarization. These emissions are associated with an electron temperature anisotropy α=T⊥e/T||e>1 consistent with the linear theory of whistler mode anisotropy instability. When the whistler mode emissions are observed the measured electron anisotropy varies inversely with β||e (the ratio of the electron parallel pressure to the magnetic pressure) as predicted by Gary and Wang (1996). Narrow band whistler emissions correspond to the small α existing before dipolarization whereas the broad band emissions correspond to large α observed during and after dipolarization. The energy in the whistler mode is leaving the current sheet and is propagating along the background magnetic field, towards the Earth. A simple time-independent description based on the Liouville's theorem indicates that the electron temperature anisotropy decreases with the distance along the magnetic field from the equator. Once this variation of α is taken into account, the linear theory predicts an equatorial origin for the whistler mode. The linear theory is also consistent with the observed bandwidth of wave emissions. Yet, the anisotropy required to be fully consistent with the observations is somewhat larger than the measured one. Although the discrepancy remains within the instrumental error bars, this could be due to time-dependent effects which have been neglected. The possible role of the whistler waves in the substorm process is discussed.

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