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Whistlers and Related Ionospheric Phenomena
01 Jun 1965-
About: The article was published on 1965-06-01 and is currently open access. It has received 1047 citations till now.
Citations
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TL;DR: Pitch angle diffusion rates due to Coulomb collisions and resonant interactions with plasmaspheric hiss, lightning-induced whistlers and anthropogenic VLF transmissions are computed for inner magnetospheric electrons as discussed by the authors.
Abstract: Pitch angle diffusion rates due to Coulomb collisions and resonant interactions with plasmaspheric hiss, lightning-induced whistlers and anthropogenic VLF transmissions are computed for inner magnetospheric electrons. The bounce-averaged, quasi-linear pitch angle diffusion coefficients are input into a pure pitch angle diffusion equation to obtain L and energy dependent equilibrium distribution functions and precipitation lifetimes. The relative effects of each scattering mechanism are considered as a function of electron energy and L shell. Model calculations accurately describe the enhanced loss rates in the slot region, as well as reduced scattering in the heavily populated inner radiation belt. Predicted electron distribution function calculations in the slot region display a characteristic “top hat” distribution which is supported by observations. Inner zone electron lifetimes based on observed decay rates of the Starfish electron population are in approximate agreement with model predictions.
500 citations
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TL;DR: In this article, the authors derived the relativistic second-order resonance condition for a whistler-mode wave with a varying frequency and found that the seeds of chorus emissions with a rising frequency are generated near the magnetic equator as a result of a nonlinear growth mechanism that depends on the wave amplitude.
Abstract: [1] The generation process of whistler-mode chorus emissions is analyzed by both theory and simulation. Driven by an assumed strong temperature anisotropy of energetic electrons, the initial wave growth of chorus is linear. After the linear growth phase, the wave amplitude grows nonlinearly. It is found that the seeds of chorus emissions with rising frequency are generated near the magnetic equator as a result of a nonlinear growth mechanism that depends on the wave amplitude. We derive the relativistic second-order resonance condition for a whistler-mode wave with a varying frequency. Wave trapping of resonant electrons near the equator results in the formation of an electromagnetic electron hole in the wave phase space. For a specific wave phase variation, corresponding to a rising frequency, the electron hole can form a resonant current that causes growth of a wave with a rising frequency. Seeds of chorus elements grow from the saturation level of the whistler-mode instability at the equator and then propagate away from the equator. In the frame of reference moving with the group velocity, the wave frequency is constant. The wave amplitude is amplified by the nonlinear resonant current, which is sustained by the increasing inhomogeneity of the dipole magnetic field over some distance from the equator. Chorus elements are generated successively at the equator so long as a sufficient flux of energetic electrons with a strong temperature anisotropy is present.
485 citations
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TL;DR: In this article, a brief review of radiation belt electron losses is presented, which are vitally important for controlling the dynamics of the radiation belts and their relative importance to the overall rate of loss.
460 citations
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TL;DR: In this paper, it was shown that Extremely Low Frequency (low frequency) or "lion" roars are closely coupled to quasi-periodic, large scale magnetosheath structures.
Abstract: It is shown that Extremely Low Frequency, or 'lion' roars are closely coupled to quasi-periodic, large scale magnetosheath structures. Because the latter are waves generated by the drift mirror instability, an attempt is made to identify and describe the magnetic and plasma features associated with this instability. Observations and analyses of the large scale structures using ISEE 1 and 2 data for the earth's magnetosheath and Pioneer 11 data for Jupiter and Saturn are presented, along with the background of the drift mirror waves. The cyclotron and drift mirror instabilities occurring in the magnetosheath are natural relaxation processes which reduce the plasma pressure anisotropies created by preferential heating of the solar wind plasma as it passes through the bow shock, as well as the compression occurring when the plasma and fields approach the near-subsolar magnetopause.
400 citations
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TL;DR: In this article, a sine-wave parametric model with a variable amplitude was used to analyze the lower band of chorus below one half of the electron cyclotron frequency, measured at a radial distance of 4.4 Earth's radii, within a 2000 km long source region located close to the equator.
Abstract: We discuss chorus emissions measured by the four Cluster spacecraft at close separations during a geomagnetically disturbed period on 18 April 2002. We analyze the lower band of chorus below one half of the electron cyclotron frequency, measured at a radial distance of 4.4 Earth's radii, within a 2000 km long source region located close to the equator. The characteristic wave vector directions in this region are nearly parallel to the field lines and the multipoint measurement demonstrates the dynamic character of the chorus source region, changing the Poynting flux direction at time scales shorter than a few seconds. The electric field waveforms of the chorus wave packets (forming separate chorus elements on power spectrograms) show a fine structure consisting of subpackets with a maximum amplitude above 30 mV/m. To study this fine structure we have used a sine-wave parametric model with a variable amplitude. The subpackets typically start with an exponential growth phase, and after reaching the saturation amplitude they often show an exponential decay phase. The duration of subpackets is variable from a few milliseconds to a few tens of milliseconds, and they appear in the waveform randomly, with no clear periodicity. The obtained growth rate (ratio of the imaginary part to the real part of the wave frequency) is highly variable from case to case with values obtained between a few thousandths and a few hundredths. The same chorus wave packets simultaneously observed on the different closely separated spacecraft appear to have a different internal subpacket structure. The characteristic scale of the subpackets can thus be lower than tens of kilometers in the plane perpendicular to the field line, or hundreds of kilometers parallel to the field line (corresponding to a characteristic time scale of few milliseconds during the propagation of the entire wave packet). Using delays of time-frequency curves obtained on different spacecraft, we have found the same propagation direction as obtained from the simultaneous Poynting flux calculations. The delays roughly correspond to the whistler-mode group velocity estimated from the cold plasma theory. We have also observed delays corresponding to antiparallel propagation directions for two neighboring chorus wave packets, less than 0.1 s apart.
395 citations
References
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TL;DR: In this article, the geomagnetic field boundary was determined using data obtained from a magnetometer on the explorer Explorer XI and the magnetometer was used to measure the magnetic field boundary.
Abstract: Determination of the geomagnetic field boundary using data obtained from a magnetometer on the explorer xii
282 citations
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TL;DR: In this article, the relativistic Schroedinger equation of an electron moving perpendicularly to a magnetic field H, can be reduced to the equation of the harmonic oscillator, and formulas were derived by means of the Boltzman transfer equation, taking into account the dependence of the electron mass on kinetic energy.
Abstract: The Schroedinger equation of an electrons moving perpendicularly to a magnetic field H, can be reduced to the equation of the harmonic oscillator. Using the relativistic Schroedinger equation and neglecting the spin, equations are found for the kinetic energy levels of the electron. Formulas were derived by means of the Boltzman transfer equation, taking into account the dependence of the electron mass on kinetic energy. (A.C.)
276 citations
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TL;DR: In this article, the precipitation of electrons with energy Ee ≥ 40 kev into the atmosphere over North America is analyzed using three directional Geiger tubes on the magnetically oriented satellite Injun 3.
Abstract: The precipitation of electrons with energy Ee ≥ 40 kev into the atmosphere over North America is analyzed. Measurements were made principally with three directional Geiger tubes on the magnetically oriented satellite Injun 3. It is shown that the intensity of electrons mirroring at the satellite altitude increases rather than decreases when precipitation occurs, for example, over an aurora. The precipitation process is such that the angular distribution of electrons tends to approach isotropy over the upper hemisphere at the satellite altitude. The flux of electrons with Ee ≥ 40 kev backscattered by the atmosphere is about ten per cent of the precipitated flux. No events have been found where the upflux exceeded the downflux, and it is concluded that most acceleration processes take place high above the satellite, accelerating electrons preferentially parallel to the magnetic field lines. It is shown that electrons with Ee ≥ 1 Mev trapped around L ∼ 4 are not perturbed when electrons with Ee ≳ 40 kev are precipitated at the same place, and so it is considered that the precipitation is not caused just by a gross change in the magnetic field producing lowered mirror points. The dependence of precipitation on Kp, local and real time, L, and so on is summarized and the implications are discussed.
214 citations
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TL;DR: In this article, the role of VLF waves in precipitating fast electrons is studied and it is found that, by Doppler-shifting whistler frequencies (1−10 kc/s) up to the local Larmor frequency, a resonant interaction of the type proposed by Dragt and Wentzel (for interaction of protons with hydromagnetic waves) can cause the mirror points of the electrons to move randomly.
Abstract: The role of VLF waves in precipitating fast electrons is studied. It is found that, by Doppler-shifting whistler frequencies (1–10 kc/s) up to the local Larmor frequency, a resonant interaction of the type proposed by Dragt and Wentzel (for interaction of protons with hydromagnetic waves) can cause the mirror points of the electrons to move randomly. The conditions for resonance lead to a very characteristic dependence on L of the regions of the magnetosphere where VLF waves can effectively precipitate electrons. In general, one expects to see, in a plot of flux versus L, two peaks separated by a broad minimum, the first peak near L ≃ 1.2 and the second near L ≃ 2. Such peaks have been seen by several experimenters. In certain regions of space it may be that whistlers can dominate the lifetimes of trapped electrons, especially for L ≳ 2.
112 citations